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Department of Civil and Environmental Engineering

Stanford University

Report No. 186 August 2014

Large-scale Tests of Seismically Enhanced Planar Walls for Residential Construction

By

Amy Hopkins, Benjamin V. Fell,

Gregory G. Deierlein, and Eduardo Miranda

The John A. Blume Earthquake Engineering Center was established to promote research and education in earthquake engineering. Through its activities our understanding of earthquakes and their effects on mankind’s facilities and structures is improving. The Center conducts research, provides instruction, publishes reports and articles, conducts seminar and conferences, and provides financial support for students. The Center is named for Dr. John A. Blume, a well-known consulting engineer and Stanford alumnus.

Address:

The John A. Blume Earthquake Engineering Center Department of Civil and Environmental Engineering Stanford University Stanford CA 94305-4020

(650) 723-4150 (650) 725-9755 (fax) [email protected] http://blume.stanford.edu

©2014 The John A. Blume Earthquake Engineering Center

i

ABSTRACT

As part of an investigation to enhance the seismic performance of light-frame residential

structures by reducing damage to partition walls and other deformation-sensitive components, this

report describes the testing and experimental results of twenty full-scale gypsum-sheathed walls.

The experiments investigated the effects of enhanced, inexpensive construction procedures with

the objective to increase the racking strength and stiffness of partition-type shear walls, lessening

seismic deformations. A majority of the specimens utilized wood framing members, while four

specimens featured cold-formed steel framing. The specimens were subjected to cyclic

earthquake-type loading through established loading histories for light-frame components. The

stiffness, strength, and damage progression of specimens with varying wall length, openings,

orthogonal wall returns, tie-down and anchoring configurations, and interior and exterior

sheathings are discussed. Iterative tests of specific interior wall geometries determined the

optimal construction techniques required to reduce deformations and improve life-cycle

performance. The main improvement to these specimens over typical construction was the use of

construction adhesive and mechanical fasteners to attach the sheathing to the framing. Additional

enhancements included mid-height blocking, improved corner stud assemblies, properly sized tie

downs at the ends of wall segments, exterior stucco engagement, and bent straps on the exterior

of planar wood-framed walls. The stiffness, strength, and residual capacity of specimens with

orthogonal walls increased as compared to specimens with in-plane-only shear walls.

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ACKNOWLEDGEMENTS

This research was supported by the National Science Foundation (CMMI- 1135029) through the

George E. Brown Jr. Network for Earthquake Engineering Simulation (NEESR). The advice and

collaboration with the following industry panel affiliates as part of this project is greatly

appreciated: Ben Schmidt (consultant), Rene Vignos, Geoff Bomba, Ali Roufegarinejad and

Mason Walters (Forell/Elsesser Engineers), Greg Luth (GPLA, Inc.), David Mar (Tipping-Mar),

Kelly Cobeen (WJE, inc.), John Osteraas (Exponent), and Reynaud Serrett (Santa Clara

University). Material donations from Simpson Strong-Tie is greatly appreciated as is the guidance

and insight from Steve Pryor (Simpson Strong-Tie). The staff of the CSU, Sacramento Tech

Shop, specifically James Ster and Mike Newton, were indispensable in the design and fabrication

of the testing rig, as well as furnishing photography equipment and support during test days. The

project team is indebted to the members of the Carpenter Union Local 46 who donated their time

to construct the wood-framed walls described herein. Several Cal State University, Sacramento

civil engineering undergraduate students were instrumental in the construction, installation,

testing, and data analysis of the experiment; primarily, the efforts and dedication of Maxwell

Hardy were the most beneficial to the project, along with other assistance from Vandalist Kith

and Nelson Tejada. Finally, the authors recognize the collegiality and support from doctoral

candidates at Stanford University – Scott Swensen, Cristian Acevedo, and Ezra Jampole – who

have worked alongside the authors on other aspects of this multifaceted NSF/NEESR project.

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TABLE OF CONTENTS Page

Abstract ............................................................................................................................................. i

Acknowledgements .......................................................................................................................... ii

List of Tables .................................................................................................................................. ix

List of Figures ................................................................................................................................. xi

Chapter

1. INTRODUCTION ...................................................................................................................... 1

1.1 Motivation ........................................................................................................................... 1

1.2 Objectives and Scope .......................................................................................................... 4

1.3 Organization and Outline .................................................................................................... 5

2. SUMMARY OF PREVIOUS STUDIES ON LIGHT-FRAME CONSTRUCTION ............... 10

2.1 Introduction ....................................................................................................................... 10

2.2 Current Seismic Design Approaches for Light-Frame Buildings ..................................... 11

2.3 Past Research on Light-Frame Construction (Simulation and Testing) ............................ 12

2.4 Gypsum Sheathed Partition Walls by McMullin and Merrick (2001) .............................. 15

2.5 Exterior Walls by Arnold et al. (2003) .............................................................................. 16

2.6 Components of Partition Walls by Swensen et al. (2012) ................................................. 17

2.7 Typical Construction Review ............................................................................................ 19

2.7.1 Typical Wood-frame Construction .......................................................................... 19

2.7.2 Typical Steel-frame Construction ............................................................................ 20

3. TESTING PROGRAM ............................................................................................................. 33

3.1 Introduction ....................................................................................................................... 33

3.2 Test Setup .......................................................................................................................... 33

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3.3 Wall Construction Details and Material Properties ........................................................... 35

3.3.1 Wood Framing ......................................................................................................... 35

3.3.2 Steel Framing ........................................................................................................... 36

3.3.3 Sheathing ................................................................................................................. 36

3.4 Test Matrix ........................................................................................................................ 37

3.5 Loading History ................................................................................................................. 38

3.6 Instrumentation .................................................................................................................. 39

4. EXPERIMENTAL RESULTS OF CYCLIC TESTED PLANAR WOOD-FRAMED

WALLS ..................................................................................................................................... 68

4.1 Introduction ....................................................................................................................... 68

4.2 Planar Control Test: W1 .................................................................................................... 69

4.2.1 Summary and Overall Behavior ............................................................................... 70

4.2.2 Observed Behavior 0-0.5% Interstory Drift ............................................................. 70

4.2.3 Observed Behavior Post 0.5% Interstory Drift ........................................................ 71

4.3 Planar Wall Tests With Unibody Enhancements: W2 Through W6 ................................. 72

4.3.1 W2: Characteristics .................................................................................................. 73

4.3.1.1 W2: Summary and overall behavior .............................................................. 73

4.3.1.2 W2: Observed behavior 0-0.5% interstory drift ............................................ 74

4.3.1.3 W2: Observed behavior post 0.5% interstory drift ........................................ 75


4.3.2.1 W3: Summary and overall Behavior ............................................................. 76




v









4.3.5.1 W6: Summary and overall behavior ............................................................... 85



4.4 Planar Wall Tests With End Returns and Unibody Enhancements: W7 and W8 ............. 86






4.4.2.1 W8: Summary and overall Behavior ............................................................. 91



4.5 Planar Wall Tests With Openings, Varying Aspect Ratios and Unibody

Enhancements: W9 Through W11 .................................................................................... 92



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4.5.1.3 W9: Observed behavior post 0.5% interstory drift ......................................... 96

4.5.2 W10: Characteristics ................................................................................................ 96

4.5.2.1 W10: Summary and overall behavior ............................................................ 96

4.5.2.2 W10: Observed behavior 0-0.5% interstory drift .......................................... 97

4.5.2.3 W10: Observed behavior post 0.5% interstory drift ...................................... 98

4.5.3 W11: Characteristics ................................................................................................ 98

4.5.3.1 W11: Summary and overall behavior ............................................................ 98

4.5.3.2 W11: Observed behavior 0-0.5% interstory drift .......................................... 99

4.5.3.3 W11: Observed behavior post 0.5% interstory drift .................................... 100

5. EXPERIMENTAL RESULTS OF CYCLIC TESTED PLANAR STEEL-FRAMED

WALLS ................................................................................................................................... 150

5.1 Introduction ..................................................................................................................... 150

5.2 Planar Control Test: S1 ................................................................................................... 151

5.2.1 Summary and Overall Behavior ............................................................................. 151

5.2.2 Observed Behavior 0-0.5% Interstory Drift ........................................................... 151

5.2.3 Observed Behavior Post 0.5% Interstory Drift ...................................................... 152

5.3 Planar Wall Tests With Unibody Enhancements: S2 Through S4 .................................. 153

5.3.1 S2: Characteristics ................................................................................................. 154

5.3.1.1 S2: Summary and overall behavior ............................................................. 155

5.3.1.2 S2: Observed behavior 0-0.5% Interstory Drift .......................................... 155

5.3.1.3 S2: Observed behavior post 0.5% Interstory Drift ...................................... 156



vii

5.3.2.2 S3: Observed behavior 0-0.5% interstory drift ............................................ 157

5.3.2.3 S3: Observed behavior post 0.5% interstory drift ....................................... 158



5.3.3.2 S4: Observed behavior 0-0.5% interstory drift ............................................ 160

5.3.3.3 S4: Observed behavior Post 0.5% interstory drift ....................................... 160

6. EXPERIMENTAL RESULTS OF WOOD-FRAMED WALLS WITH EXTERIOR

SHEATHING CONDITIONS ................................................................................................ 177

6.1 Introduction ..................................................................................................................... 177

6.2 Planar Wall Tests With Unibody Enhancements and Exterior Sheathing ....................... 177

6.2.1 W-DG: Characteristics ........................................................................................... 178

6.2.1.1 W-DG: Summary and overall behavior ....................................................... 179

6.2.1.2 W-DG: Observed behavior 0-0.5% interstory drift ..................................... 179

6.2.1.3 W-DG: Observed behavior post 0.5% interstory drift ................................. 180

6.2.2 W-PLY: Characteristics ......................................................................................... 181

6.2.2.1 W-PLY: Summary and overall behavior ..................................................... 181

6.2.2.2 W-PLY: Observed behavior 0-0.5% interstory drift ................................... 181

6.2.2.3 W-PLY: Observed behavior post 0.5% interstory drift ............................... 182

6.2.3 W-STU: Characteristics ......................................................................................... 183

6.2.3.1 W-STU: Summary and overall behavior ..................................................... 184

6.2.3.2 W-STU: Observed behavior 0-0.5% interstory drift ................................... 184

6.2.3.3 W-STU: Observed behavior post 0.5% interstory drift ............................... 185

7. CONCLUSIONS AND FUTURE WORK ............................................................................. 202

7.1 Summary ......................................................................................................................... 202

viii

7.1.1 Interior Wood-framed Specimens .......................................................................... 203

7.1.2 Interior Steel-framed Specimens ............................................................................ 204

7.1.3 Exterior Wood-framed Specimens ......................................................................... 205

7.2 Conclusions for Unibody Construction Techniques ........................................................ 206

7.3 Future Work and Recommendations ............................................................................... 207

References .................................................................................................................................... 212

APPENDIX A: Uplift Forces Recorded at Tie-Down Units and Instrumented Anchor Bolts .... 218

ix

LIST OF TABLES

Tables Page

Table 2.1 Abbreviated test matrix and results for McMullin and Merrick ................................... 22

Table 3.1 Test matrix .................................................................................................................... 41

Table 3.2 Test matrix uplift constraints and locations ................................................................... 42

Table 3.3 Loading protocol ............................................................................................................ 42

Table 3.4 Nail and screw information ............................................................................................ 43

Table 3.5 Time intervals for lumber and adhesive ......................................................................... 43

Table 3.6 Reported requirements and capacities for Simpson Strong-tie wood tie-downs ........... 44

Table 3.7 Liquid Nails construction adhesive reported shear strength .......................................... 44

Table 3.8 Reported requirements and capacities for Simpson Strong-tie light-gage steel

tie-downs ....................................................................................................................... 44

Table 3.9 Loctite construction adhesive reported shear strength ................................................... 44

Table 3.10 Instruments for Specimens W1 through W6 ................................................................ 45

Table 3.11 Instruments for specimens W7, W8, and W10 ............................................................ 46

Table 3.12 Instruments for wood-framed specimens with returns and door openings ................. 47

Table 3.13 Instruments for exterior specimens (W-DG, W-PLY, and W-STU) ........................... 48

Table 3.14 Camera locations for time-lapse cameras .................................................................... 49

Table 4.1 One-sided stiffness and strength of interior wood-framed wall specimens ................ 101

Table 4.2 Anchor bolt pretension forces at beginning of test (lbs) .............................................. 102

Table 4.3 Tie down pretension forces at beginning of test (lbs) .................................................. 102

Table 5.1 One-sided stiffness and strength of steel walls ........................................................... 161



x

Table 6.1 Stiffness and strength of exterior wood-framed walls ................................................ 187



Table 7.1 Summary of interior specimen behaviors .................................................................... 209

Table 7.2 Summary of exterior specimen behaviors .................................................................... 209

xi

LIST OF FIGURES

Figures Page

Figure 1.1 Inelastic structural behavior with large R-factor design contrasted against a limited

ductility system through elastic design .......................................................................... 8

Figure 1.2 Typical floor plan demonstrating additional wall length and strength capacity

available through (a) only including exterior walls in the lateral force resisting

system and (b) using all interior and exterior walls to resist seismic forces. ................. 9

Figure 2.1 Wood panel wall force-deformation response and associated damage states (van de

Lindt, 2004).................................................................................................................. 23

Figure 2.2 Construction framing elevation for specimens (a) type 1 and (b) type 2 of McMullin

and Merrick research ................................................................................................... 24

Figure 2.3 Construction framing elevation for (a) walls 1 and 3 and (b) walls 2 and 4 of Arnold

et al. research ............................................................................................................... 25

Figure 2.4 Typical specimen cross-section installed in frame for Arnold et al. research. ............. 26

Figure 2.5 Construction framing for (a) fastener and (b) panel tests of Swensen et al. research .. 27

Figure 2.6 Monotonic backbone curves for (a) wood-framed specimens and (b) steel-framed

specimens of the fastener tests of Swensen et al. research ......................................... 28

Figure 2.7 Cyclic backbone cuves for (a) wood-framed specimens and (b) steel-framed

specimens of the panel tests of Swensen et al. research .............................................. 29

Figure 2.8 Suggested corner stud assemblies for (a) corners of exterior walls and (b) at the

intersections of partition walls of wood-framed structures (ANSI, 2005) ................... 30


intersections of partition walls of light-gage steel-framed structures

(NAFSA, 2000) ............................................................................................................ 31

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Figure 2.10 Anchorage requirements for steel-framed specimens (NAFSA, 2000). ..................... 32

Figure 3.1 Loading protocol .......................................................................................................... 50

Figure 3.2 Test frame component indentification and dimensions ................................................ 51

Figure 3.3 Test frame with (a) 8 ft. specimen and (b) 16 ft. specimen installed ............................ 52

Figure 3.4 Stiffener assemblies on the W8x48 base beam ............................................................. 53

Figure 3.5 Bell crank used to rotate the forces applied to the specimen ....................................... 54

Figure 3.6 Loading link (a) as designed in the manufacturing plans and (b) as installed in the

test frame ...................................................................................................................... 55

Figure 3.7 Out-of-plane restrictions for top loading beam; (a) Plan and (b) section view of the

beam and (c) Turnbuckles used to pretension rods ...................................................... 56

Figure 3.8 Section view of wall in test rig; (a) Wood-framed specimen and (b) steel-framed

specimen ...................................................................................................................... 57

Figure 3.9 Corner and end details; End of planar wall: (a) Wood-framed, (d) Steel-framed;

T-shape corner assembly: (b) Wood-framed, (e) Steel-framed; (c) Wood-framed

L-shape corner assembly .............................................................................................. 58

Figure 3.10 Wallboard layout for (a) 8 ft. walls, (b) 16 ft. walls, and (c) Exterior face of external

walls ........................................................................................................................... 59

Figure 3.11 Approximate lumber moisture level for wood specimens .......................................... 60

Figure 3.12 Samples of instrumentation used to measure frame and wallboard behaviors;

(a) Strain gage on loading link, (b) LVDT measuring stud uplift, and (c) string

potentiometer measureing specimen displacement .................................................... 61

Figure 3.13 Applied force versus average recorded strain used for link calibration .................... 62

Figure 3.14 Planar wall instrumentation (W1-W6 and S1-S2) ...................................................... 63

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Figure 3.15 Instrumentation for specimens with returns and no openings

(W7, W8, W10, S3 and S4) ........................................................................................ 64

Figure 3.16 Instrumentation for specimens with door openings (W9 and W11) ........................... 65

Figure 3.17 Exterior wall instrumentation (W-DG, W-PLY, and W-STU); (a) On interior face

and (b) on exterior face .............................................................................................. 66

Figure 3.18 Example of how damage propagation for each set of cycles is highlighted using

different colors ........................................................................................................... 67

Figure 4.1 South elevation construction framing and details for specimens W1-W6 .................. 103

Figure 4.2 Out-of-plane measurements for specimen W1; (a) Locations of the measurements

and (b) Measured and calculated displacements ........................................................ 104

Figure 4.3 Force-deformation response for 0-0.5% interstory drift cycles for specimens

W1-W6 ....................................................................................................................... 105

Figure 4.4 Fastener damage states; (a) Paint and mud cracking over screw at 0.1% and

(b) Popped screw heat at 0.3% ................................................................................... 106

Figure 4.5 Specimen W1 damage illustration at (a) 0.5% interstory drift and (b) End of test ..... 107


W1-W6 ....................................................................................................................... 108

Figure 4.7 Wallboard separation and sliding in W1 at (a) negative and (b) positive specimen

deformations .............................................................................................................. 109

Figure 4.8 Cyclic backbone curve comparisons for specimens W1-W6 ..................................... 110

Figure 4.9 Images demonstrating gypsum wallboard failures as evidenced by residual paper

backing on (a) double end stud and (b) interior stud ................................................ 111

Figure 4.10 Images showing damages at bottom of sill plate of W2; (a) Crack and screws

popping on South face at 0.3% interstory drift, (b) Crack location compared to

xiv

top of sill plate (0.3%), and (c) Wallboard disengaged from studs at 2.0% ............. 112

Figure 4.11 Specimen W2 damage illustration at (a) 0.5% interstory drift and (b) End of test... 113

Figure 4.12 Displacement time history of wallboard sheathing and frame members for W2

measuring (a) the horizontal displacement at bottom of wallboard and top of

frame and (b) vertical uplift of wallboard and end stud ........................................... 114

Figure 4.13 Neoprene pads at anchor bolts for specimen W3 ..................................................... 115





Figure 4.16 Stiffness enhanced tie down used for specimen W4 prior to installation ................. 118

Figure 4.17 Specimen W4 damage illustration at (a) 0.5% interstory drift and (b) End of test .. 119




Figure 4.19 End stud and tie down behavior in W4 at (a) positive and (b) negative specimen

deformations ............................................................................................................ 121

Figure 4.20 Uplift constraint assembly consisting of tie down and bent strap for W5 ................ 122




frame and (b) vertical uplift of wallboard and end stud. .......................................... 124


xv




Figure 4.25 Construction framing for Specimens W7 and W8; (a) East elevation, (b) South

elevation, and (c) Plan view ..................................................................................... 127

Figure 4.26 Cyclic backbone curve comparisons for specimens W1 and W6 - W8 .................... 128

Figure 4.27 Observed damages of specimen W7; (a) Hairline crack formed at corner between

main wall and return wall, (b) Buckling of wallboard at corner, (c) Crack on

return wall caused by failure of corner stud assembly, and (d) Failure of stud

assembly ................................................................................................................... 129


W7 – W8 .................................................................................................................. 130

Figure 4.29 Specimen W7 damage illustration at (a) 0.5% interstory drift and (b) End of test . 131





W7 – W8 ................................................................................................................. 133





Figure 4.34 Improved corner stud assembly failure on specimen W8 ......................................... 136

Figure 4.35 Cyclic backbone curve comparisons for specimens W6 and W8 – W11 ................. 137

xvi

Figure 4.36 Curve fits capturing the behavior for varying aspect ratios; (a) Strength capacity

and (b) stiffness ........................................................................................................ 138

Figure 4.37 Construction framing for Specimen W9; (a) East elevation, (b) South elevation,

and (c) Plan view ...................................................................................................... 139


W9 – W11 ................................................................................................................ 140

Figure 4.39 Specimen W9 damage illustration at (a) 0.5% interstory drift and (b) End of test . 141





W9 – W11 ................................................................................................................ 143

Figure 4.42 South elevation construction framing for Specimen W10 ........................................ 144

Figure 4.43 Specimen W10 damage illustration at 0.5% interstory drift .................................... 145




Figure 4.45 South elevation construction framing for Specimen W11 ........................................ 147

Figure 4.46 Specimen W11 damage illustration at 0.5% interstory drift .................................... 148



frame and (b) vertical uplift of wallboard and end stud .......................................... 149

Figure 5.1 South elevation construction framing and details for specimens S1 and S2 .............. 162

Figure 5.2 Force-deformation response for 0-0.5% interstory drift cycles for S1 – S4 ............... 163

xvii

Figure 5.3 Specimen S1 damage illustration at (a) 0.5% interstory drift and (b) End of test ..... 164

Figure 5.4 Fastener damage states of screws popping showing (a) only a visible divot and

(b) cracked mud with screw fully disengaged from wallboard ................................. 165

Figure 5.5 Force-deformation response for 0-2.5% interstory drift cycles for S1 – S4 ............... 166

Figure 5.6 Steel framing chosen to improve unibody enhancements features (a) grooved

flanges of studs improve bonding of construction adhesive as shown when

(b) wallboard was removed after test ........................................................................ 167

Figure 5.7 Cyclic backbone curve comparisons for specimens S1 – S4 ...................................... 168

Figure 5.8 Specimen S2 damage illustration at (a) 0.5% interstory drift and (b) End of test ..... 169

Figure 5.9 Displacement time history of wallboard sheathing and frame members for S2



Figure 5.10 Construction framing for Specimens S3 and S4 (a) East elevation, (b) South

elevation, and (c) Plan view ..................................................................................... 171

Figure 5.11 Specimen S3 damage illustration at (a) 0.5% interstory drift and (b) End of test ... 172




Figure 5.13 Spacers added to blocking of specimen W4; (a) Image of blocking spacer material

and (b) Locations of blocking in plan view of specimen ........................................ 174

Figure 5.14 Specimen S4 damage illustration at (a) 0.5% interstory drift and (b) End of test ... 175




xviii

Figure 6.1 Construction plans for exterior wall specimens featuring (a) the East elevation,

(b) the South elevation, and (c) plan view ................................................................ 188

Figure 6.2 Cyclic backbone curve comparisons for exterior specimens ..................................... 189

Figure 6.3 Force-deformation response for 0-0.5% interstory drift cycles for exterior walls .... 190

Figure 6.4 Force-deformation response for 0-2.5% interstory drift cycles for exterior walls ..... 191

Figure 6.5 Specimen W-DG damage illustration at 0.5% interstory drift on (a) North

(Gypsum Wallboard) face and (b) South (DensGlass® Wallboard) face ................... 192

Figure 6.6 Displacement time history of wallboard as compared to the frame for W-DG

(a) interior and (b) exterior wallboard horizontal displacements; (c) interior and

(d) exterior wallboard vertical displacements ........................................................... 193

Figure 6.7 Specimen W-DG damage illustration at end of test on (a) North (Gypsum

Wallboard) face and (b) South (DensGlass® Wallboard) face ................................... 194

Figure 6.8 Specimen W-PLY damage illustration at 0.5% interstory drift on (a) North

(Gypsum Wallboard) face and (b) South (Plywood) face ........................................ 195

Figure 6.9 Displacement time history of wallboard as compared to the frame for W-PLY


(d) exterior wallboard vertical displacements .......................................................... 196

Figure 6.10 Specimen W-PLY damage illustration at end of test on (a) North (Gypsum

Wallboard) face and (b) South (Plywood) face ........................................................ 197

Figure 6.11 Construction of W-STU (a) after Densglass® sheathing is installed, (b) after

building paper and wire lath are installed, (c) after scratch coat, (d) after brown

coat, (e) after finish coat .......................................................................................... 198

Figure 6.12 Specimen W-STU damage illustration at 0.5% interstory drift on (a) North

(Gypsum Wallboard) face and (b) South (Stucco) face .......................................... 199

xix

Figure 6.13 Displacement time history of wallboard as compared to the frame for W-STU


(d) exterior wallboard vertical displacements .......................................................... 200

Figure 6.14 Specimen W-STU damage illustration at end of test on (a) North (Gypsum

Wallboard) face and (b) South (Stucco) face ........................................................... 201

Figure 7.1 Cyclic backbone curves for wood and steel specimens; (a) Interior wood

specimens, (b) interior steel specimens, and (c) exterior wood specimens ............... 210

Figure 7.2 Cyclic backbone curves for interior and steel specimens; (a) Typical construction

specimens, (b) planar unibody specimens, and (c) unibody specimens with returns . 211

1

CHAPTER 1

INTRODUCTION

1.1 Motivation

Current seismic building code provisions use response modification coefficients, or R-

factors (R > 1), to reduce the required strength of the lateral force resisting system below the

elastic force demand in a design level event, thereby allowing for inelastic structural response and

an increase in the ductility capacity of the components (ASCE, 2010). Common values of the

response modification coefficient range from 3 to 8 for low and high ductility systems,

respectively, with 6.5 as a common R-value for light-frame residential structures. Figure 1.1

demonstrates the force-deformation relationship of a low R-value and high R-value response. As

the lateral system deforms inelastically during earthquake loading, both the load carrying

components and non-structural components may undergo significant damaged. In fact, because

of the brittle behavior of common finish materials such as stucco, drywall and plaster, the damage

to non-structural components typically accounts for the majority of post-event renovations costs

(Comerio, 1998). While the elastic design and damage-free response may be economically

infeasible for multi-story steel or reinforced concrete lateral systems, residential structures have

considerable differences in terms of common room dimensions, floor mass, and function. As part

of a multi-phase Network for Earthquake Engineering (NEES) project, this thesis investigates the

response of planar wall components during earthquake-type loading towards a limited-ductility

(elastic) design methodology for residential structures.

Light-frame residential structures include nonstructural and structural components framed

with common lumber cross-sections such as 2x4s and 2x6s or light gage rolled steel cross-

sections with exterior Oriented Strand Board (OSB) or Plywood sheathing and composite gypsum

board for interior finishes. Lateral loading from wind or earthquake is transferred from the floor

2

or roof mass to the foundation through exterior walls sheathed with OSB and nail fasteners at

minimum spacing distances to develop the strength of the panel board. However, unlike high-rise

steel and concrete structures, the strength of interior partitions and finishes in residential

structures are a larger percentage of the stiffness and strength of the main lateral load resisting

system. For example, McMullin and Merrick (2001) demonstrated the one-sided strength of

gypsum-sheathed shear walls to be as large as 200 lb/ft, while OSB-sheathed and plywood-

sheathed walls have strengths up to 520 lb/ft and 870 lb/ft, (Breyer et al., 2007). In addition, the

mass carried by lateral components in residential structures are significantly smaller as compared

to the mass from concrete slabs in office buildings with steel and reinforced concrete lateral

systems. Through feasible load transfer mechanisms from the floor mass, to the non-structural

shear wall and, finally, to the foundation, the strength of the wall can be integrated into the lateral

system thereby allowing the entire structure to resist the seismic forces with improved strength

and performance. Figure 1.2 demonstrates the additional wall length available through the

inclusion of the non-structural shear walls on a typical floor plan.

The experimental results presented in this thesis demonstrate the strength and stiffness

characteristics of individual planar shear walls with seismic enhancements to increase

performance in the context of a limited ductility system. A common attribute of light-framed

shear walls, regardless of the sheathing material, is the large amount of inelasticity needed to

reach the peak force capacity of the wall. Thus, mobilizing the wall to relatively high drift levels,

on the order of 1.0%-1.5% interstory drift, is needed to reach their full strength. However, the

same testing series demonstrated fastener damage begins as soon as 0.2% interstory drift, with

significant damage necessitating replacement at 1.0% and total loss of economic value at

approximately 2.0% (McMullin and Merrick, 2001). While this performance meets the life-safety

and collapse prevention limit state, the large interstory drifts are certainly beyond the immediately

3

occupancy and operational limit states (FEMA, 2004a, 2004b). To decrease the deformation

needed to achieve peak strength, the majority of the tests reported in this thesis utilize

construction adhesive between the wood or metal framing members and sheathing materials is

used to create a stiffness-enhanced, limited ductility response, such that the strength is governed

by the adhesive strength, rather than fastener spacing. Additional modifications include fastener

enhancements (Swensen, 2012), uplift constraints, and fiber-composite materials for interior and

exterior facades.

Within the proposed “unibody” construction methodology, the building components are

designed such that architectural and exterior structural walls act together in shear to resist

earthquake loads and deformations. By engineering the architectural building components of the

structure to contribute to the lateral force resisting system, it may be possible for the residence to

be damage free after a seismic event. The planar walls tested within this investigation

demonstrate how this design procedure significantly increases the strength and stiffness of the

walls, thereby decreasing deformation demands, displacement-sensitive damage, and repair

cost/time.

Reducing damage and repairs is especially important for residential structures

considering a) prohibitively expensive earthquake-insurance premiums in regions of high seismic

risk, and b) safety risks associated with displacing a large percentage of the population after a

large earthquake. Referring to the latter point, the Katrina hurricane demonstrated the large toll

to society when residences are uninhabitable for an extended period. While the current structural

design approach may satisfy the life-safety limit state during the earthquake event itself, it will

arguably create a more desperate challenge during the post-event response. In fact, Kircher

estimates that 160,000 to 250,000 damaged homes and millions of displaced people in the case of

a large event in the California Bay-Area (2006).

4

1.2 Objectives and Scope

As a part of a research project funded by National Science Foundation (NSF) through

NEESR, the testing program described herein develops and validates a new seismic design

concept for components of light-frame residential construction with an overall aim to improve

life-cycle seismic performance. Overall, the objectives of the large NEES project are to

investigate (a) small component tests and planar wall panel tests to develop and characterize

construction techniques of interior and exterior walls, (b) an economical low-force high-

displacement isolation system, (c) quasi-static tests of three dimensional room assemblies, and (d)

shake-table tests of a two-story residential building with seismic isolators and enhanced unibody

construction.

The wall specimens in this report follow from work at Stanford University, which

included component, fastener and material tests, along with 4 ft. x 4 ft. planar wall tests utilizing

construction adhesive between the framing members and wallboards. The results of this phase are

reported in Swensen et al. (2012) and summarized in Chapter 2 of this report. The full-scale

specimens tested at California State University, Sacramento investigate similar performance

while also introducing additional variables and details representative of current construction.

The experiments of this phase of the project investigated the effects of enhanced,

inexpensive construction procedures on full-scale planar specimens built with wood and cold-

formed steel framing members. The differing characteristic of these specimens, as compared to

typical construction techniques, was the use of construction adhesive and mechanical fasteners to

attach the sheathing to the framing members. To further investigate and reduce the effects of

deformations from earthquake-type loading, the additional objectives of the study are to

determine and document –

5

(1) The strength, stiffness, and damage progression of unibody planar wall specimens

with varying aspect ratios, openings, and orthogonal walls

(2) The optimal construction techniques required when construction adhesive is used to

install wallboard panels

The next two phases of the aforementioned NEES project, which involve the

development of an economical seismic base isolation system and quasi-static tests of room

assemblies, will be completed during the summer of 2013. The work described in this thesis is

used in the design and construction of the room assemblies, albeit these tests focus on the force-

transfer mechanism between the floor diaphragm and the planar shear walls. The final phase of

the project is a culmination of all phases of the project and features a shake table test of a two-

story residential building with enhanced unibody construction and seismic isolator, and is

scheduled to be completed during the summer of 2014.

1.3 Organization and Outline

Chapter 2 summarizes pertinent literature and design codes of previous work to contrast

performance, while also aiding in the construction techniques for the specimens conducted as part

of this research. This includes a discussion of typical construction techniques for light frame

construction based on various standards and specifications. Summarized next are the results of an

experimental project by McMullin and Merrick (2001), which investigated the seismic behavior

of gypsum-sheathed walls of various configurations in conjunction with the CUREE-Caltech

Woodframe Project. Then, the results of Arnold et al (2003) are discussed, which investigated

behavior of typical exterior wood-framed walls as part of the Earthquake Damage Assessment

and Repair Project. The chapter concludes by discussing the experiments conducted by Swensen

et al.(2012), representing the initial phase of this project which performed component and small

6

scale panel tests to determine efficient fastening and joining techniques for gypsum sheathed

walls.

Chapter 3 details the experimental setup and test rig used for the large-scale tests

described in Chapters 4-6. The chapter reviews the design of the specimens, test setup,

experimental specimen matrix, loading history, instrumentation, camera locations and testing

observations.

Chapters 4 through 6 include the test results for each of the twenty specimens tested

within this research. For each specimen, an explanation is provided for the construction details

that uniquely characterize the specimen within the test series. Then, the test results are presented

in categories of overall behavior, which includes the strength, stiffness, and primary mode of

failure, and the observed behaviors during the 0 through 0.5% interstory drift cycles and the post

0.5% interstory drift cycles, which include all observed and recorded responses of the specimen

to the applied displacements.

Chapter 4 reports the test results of the eleven interior walls of the wood-framed

experimental suite. First presented within the chapter are the results of a free-standing planar

specimen built using typical construction techniques for nonstructural partition walls and acted as

the control specimen for the remainder of the wood-framed tests. Next, the chapter provides the

results of five specimens, which featured unibody construction techniques for specimens with the

same geometry as the control test. Each of these specimens featured iterative improvements to

the construction details to increase the strength, stiffness, and damageability performance of the

specimen. Then, the chapter presents the results of two planar wall specimens with attached

orthogonal walls, which were constructed using the construction techniques of the best

performing planar specimen. These two specimens also featured iterative improvements to the

7

construction details to improve the performance of the specimen. Lastly, the chapter presents the

results of planar walls with varying aspect ratios, door openings, and orthogonal end returns.

Chapter 5 presents the test results of four interior walls with light-gage steel framing

members. Similar to the previous chapter, presented first are the results of a free-standing planar

specimen using typical construction to serve as the control specimen for the other three tests.

Presented next are the results of a planar specimen built with unibody construction techniques.

Finally, results are presented for two specimens featuring orthogonal end returns and similar

iterations to the construction techniques as the wood-framed specimens.

Chapter 6 presents test results of three wood-framed specimens representative of exterior

walls in residential structures. To simulate an external end-return condition, these specimens

featured shorter orthogonal walls attached to the planar wall to create a “C”-shaped specimen.

The interior faces of the specimens were sheathed using gypsum board and the techniques

described in Chapter 4. The exterior faces of the specimens featured different external

sheathings, including fiberglass mat sheathing, plywood, and three-coat stucco applied over

fiberglass mat sheathing.

Chapter 7 summarizes the key observations and conclusions drawn from the experiments

that may influence the geometries and construction details used for the room assembly and full-

scale shake-table tests. The chapter will also provide recommendations for future studies not

addressed as part of this investigation.

8

Force

R≅1 Response

Inelastic

Damage R>1 Response

Inelastic Damage Interstory Drift

Figure 1.1 Inelastic structural behavior with large R-factor design contrasted against a limited ductility system through elastic design.

9

(a)

(b)

Figure 1.2 Typical floor plan demonstrating additional wall length and strength capacity available through (a) only including exterior walls in the lateral force resisting system

and (b) using all interior and exterior walls to resist seismic forces.

DINING

GREAT ROOM MASTER

BEDROOM MASTER

BATH

WIC

KITCHEN

BEDROOM BEDROOM

BATH

DINING

GREAT ROOM MASTER

BEDROOM MASTER

BATH

WIC

KITCHEN

BEDROOM

BATH

BEDROOM

10

CHAPTER 2

SUMMARY OF PREVIOUS STUDIES ON LIGHT-FRAME CONSTRUCTION

2.1 Introduction

Extensive work has been conducted to investigate the behavior of light-frame

components and systems subjected to earthquake-type loading, including experimental and

analytical studies which have led to the current understanding of the response of wood and light-

gage steel-framed structures. In general, a central goal of previous studies has been on

developing a high-ductility response, allowing for large inelastic force reduction factors in the

design of typical structures. However, as demonstrated in Figure 2.1, large ductility demands

necessitate an inelastic response and associated damage states that require extensive repairs to

structural and nonstructural components alike.

In this light, this chapter summarizes several testing programs that are most pertinent to

the experiments conducted in this study. While the components described herein are meant to

create a “limited ductility” system with little, to no, inelastic deformations, the design and

construction are meant to mimic typical details of current practice as closely as possible. In

addition to the experimental studies, typical construction details for wood and light-gage steel

framing are provided, informed from current design provisions. Where appropriate, and to lessen

the magnitude of change to current practice, these details are repeated in the test specimens

described in Chapters 3-6.

The chapter begins by giving a review of a large majority of all experimental and

analytical tests conducted on residential components and systems. Next, several studies are

identified as being the most applicable and comparable to the current work including the

experimental studies by McMullin and Merrick (2001), Arnold et al. (2003) and Swensen et al.

(2012). These studies are discussed in more detail within this chapter. Finally, a review of

11

common light-frame details is provided which are informed from current design provisions and

past work. These latter sections, compared with the specimen geometry and details in Chapters 4,

5 and 6, are meant to highlight any differences in the unibody specimen design.

2.2 Current Seismic Design Approaches for Light-Frame Buildings

Seismic design requirements for light-framed systems distinguish between those

constructed with (a) wood or steel shear panels and (b) other panel materials. For systems with

wood and steel panels, the design requirements of ASCE 7 Minimum Design Loads for Buildings

and other Structures (ASCE, 2010) specify large inelastic force reduction factors of R = 6.5 to 7.0

for bearing wall and building frame systems, respectively (Cobeen et al. 2004). For light-framed

systems of other materials, such as gypsum wallboard and stucco, ASCE 7 specifies much lower

factors of R = 2 to 2.5, implying lower ductility and higher design strengths, leading to stiffer

systems with much lower drift demands. The relative strengths and stiffnesses of these systems

are illustrated in the seismic force versus drift plot of Figure 1.1

Studies conducted as part of the development of FEMA P695 Quantification of Building

Seismic Performance Factors (2009) have shown that wood panel walls designed according to

current standards just barely meet the minimum collapse safety specified in FEMA P695. For

example, in Performance Group No. PG-9 (Short Period, High Aspect Ratio) describing multi- or

1&2 family dwellings with high aspect ratio shear walls, the average adjusted collapse margin

ratio (ACMR) measuring the ratio of spectral acceleration to cause collapse in 50% of scaled

ground motions to the Maximum Considered Earthquake (MCE) acceleration is 1.89. The

established acceptance ACMR is only 1.90, thus passing by a narrow margin. Moreover, the

FEMA P695 procedures, and seismic code provisions in general, are only concerned with seismic

12

collapse safety and do not explicitly address damage control necessary for continued occupancy

or to limit economic losses.

Unlike multi-story steel and concrete framed buildings, where the façade and partitions

are generally designed to accommodate large drifts, in low-rise residential construction, the

partitions and façade are integral with the structure and will undergo the same deformations as the

primary seismic force resisting system. Consequently, where the lateral systems are designed

with high R-values, the resulting large deformations will cause significant damage to the

partitions and facades. On the other hand, these same partitions and facades can provide

additional strength and stiffness that tend to improve the seismic performance of wood and steel

shear panel systems.

In contrast to the high-ductility systems, the proposed “limited-ductility” unibody

systems with lower R-values and larger strength and stiffness have the potential to provide better

damage resistance. However, as it is commonly perceived that higher R-factors provide

improved performance, these limited-ductility systems are not widely used in high-seismic

regions. Such perceptions are compounded by the fact that there has been very little, if any,

research to establish the collapse safety performance of high-strength limited ductility systems for

high seismic regions.

2.3 Past Research on Light-Frame Construction (Simulation and Testing)

The lateral strength of wood panel walls is developed through a composite action of the

sheathing material, fasteners, and framing elements, where a majority of the strength is generated

by the sheathing material in a shear deformation mode. Inelastic action at small levels of

deformation is developed primarily at the interface between the fasteners, sheathing and framing

through deformation of the fasteners (Stewart et al., 1988) and crushing of the wood under the

13

bearing load of the fastener. While the strength capacity changes, these mechanisms are also

similar for light-gage steel-framed walls with wood paneling (Serrette, 1997). At larger

deformations, global inelastic effects are activated such as sheathing buckling and separation as

well as uplifting of the panel wall (Schmid et al., 1994). Due to this complex behavior, numerous

physical and analytical investigations have used fastener, component or full-scale tests and

analyses to explore the lateral shear strength and ductility of wood panel walls.

Research on wood panel walls extends back to the 1940s where the earlier work is

summarized in Carney (1975) and Peterson (1983). Later investigations (after 1982) are

discussed by van de Lindt (2004). The most prevalent of testing programs are full-scale

rectangular panel walls whose dimensions are typically 8-20 ft long, 6-8 ft high and 4-6 in. thick.

The panel strength capacity has been shown to increase with length (Patton-Mallory and Wolfe,

1985) and a decreased fastener spacing (Atherton, 1983), where the effective length is calculated

by subtracting the cumulative opening distances for doors and windows (Falk and Itani, 1987).

Referring to Figure 2.1 (van de Lindt, 2004), however, the lateral strength capacity is fully

developed only after significant inelastic behavior and damage to the fasteners, frame and

sheathing. While the maximum shear strength is maintained across a large range of lateral

deformation prior to strength degradation and eventual failure, the elastic region is indiscernible

in the figure and Vmax is developed only after significant damage. In fact, Ficcadenti et al.

(1998) found that the strength capacity decreases with an increased number of elastic loading

cycles, signifying that even at small displacements the components are damaged and display an

inelastic response.

Several studies (Dinehart and Shenton 1998, Dinehart et al. 1999, and Higgins 2001)

have investigated the performance of wood frame panel walls with a variety of active and passive

damping devices and concluded that damping significantly increases the energy dissipation

14

capacity of the walls. However, since these devices are activated at relatively large displacements

and velocities, the walls still develop the damage mechanisms listed in Figure 2.1 and would

require repair similar to an undamped component after a design level earthquake (van de Lindt,

2004).

Modeling efforts of wood panel shear walls range from predictive equations for strength

and stiffness (Easley et al., 1982) to nonlinear finite element modeling (Cheung and Itani, 1983).

Predictive equations are developed using physics based models to capture the inelastic

deformation modes described previously and are quite accurate in predicting the elastic stiffness

and ultimate strength capacity (McCutcheon 1985, Patton-Mallory and McCutcheon, 1987).

Studies have also shown good agreement with experimental results by representing panel walls

with uniaxial spring, beam and shell elements to model the behavior of fasteners, frame members

and sheathing, respectively (Itani and Cheung 1984, Itani and Robledo 1984, White and Dolan

1995). Other modeling techniques include a pair of diagonal springs to represent wood sheathing

(Itani et al., 1982), single degree of freedom systems (Dolan and Filiatrault, 1990), and multiple

degree of freedom systems (Foliente 1995, Dinehart and Shenton 2000, Folz and Filiatrault 2001)

calibrated from experimental programs to capture strength degradation and pinching behavior.

The Folz and Filiatrault (2001) model was developed into a program titled CASHEW (Cyclic

Analysis of SHEar Walls) and became a common tool in the engineering community to predict

panel wall behavior. Numerical models to perform nonlinear dynamic models have been

developed by Tarabia and Itani (1997), Folz and Filiatrault (2004a, 2004b) and Collins et al.

(2005). A relatively new nonlinear dynamic software package named SAPWood (van de Lindt et

al, 2010) built on the previous models and incorporates shear deformations of the walls and out-

of-plane rotations of the floor and ceiling diaphragms.

15

Similar experimental and analytical work has also been performed on nonstructural

partition walls with gypsum sheathing. While partition walls have a smaller strength capacity as

compared to wood sheathing shear walls, the force-deformation response and damage

mechanisms illustrated in Figure 2.1 are quite similar (Rihal 1984, Oliva et al. 1990, Karacabeyli

1996, McMullin and Merrick, 2001) and also develop at small levels of interstory drift.

Moreover, several investigations (Patton-Mallory and Wolfe 1985, Filiatrault et al. 2002 and

2010) have demonstrated that gypsum wallboard and stucco finishes on wood shear walls can

significantly contribute to the strength and stiffness of the wall and decrease interstory drift ratios

by up to 40% (Vance and Smith, 1996). Kanvinde and Deierlein (2006) proposed physics based

predictive models for the strength and stiffness, demonstrating strength capacities of gypsum

walls on the order of 5000-8000 lbs.

2.4 Gypsum Sheathed Partition Walls by McMullin and Merrick (2001)

As part of the CUREE-Caltech Woodframe, a project funded by the Consortium of

Universities for Research in Earthquake Engineering (CUREE), Kurt McMullin and Dan Merrick

tested seventeen specimens designed to represent standard construction of gypsum wallboard

partition walls. The main purpose of this portion of the project was to gain understanding of the

behavior of gypsum partition walls built using the standard construction practices.

All specimens, which were 8-foot high and 16-foot long, were framed with 2 in. by 4 in.

nominal dimension framing lumber and sheathed on both sides with Standard grade, ½ in.

gypsum sheathing wallboard. The varying parameters of the test matrix included fastener type

and spacing, loading protocol, fastener type and spacing, loading protocol, wallboard and opening

layout, construction methods, influence of door and floor trim and repair strategies. The

construction plans used for the specimens in this research are shown in Figure 2.2.

16

McMullin and Merrick determined that the overall behavior and levels of damage of the

specimen appeared to be related to the rigidity and geometry of the boundary elements of the

wall. Damage patterns of the specimens usually initiated during the 0.25% drift levels as cracks

at the wall penetrations and over fastener heads. Additional damages included the global

buckling of large portions of panels, and the loss of portions of panel sections and crushing of

wallboard at corners during the larger displacements.

Table 2.1 shows the two-sided maximum strength achieved by the specimens - excluding

openings - in which the gypsum wallboards were installed with screws. The maximum loads

were sustained between 1% and 1.5% drift and usually initiated one of two failure modes. The

first failure mode consisted of wallboard separation from the frame caused by fasteners being

pulled through the back of the wallboard. The second failure consisted of failure of the taped

wall joints which allowed racking movement of the individual wallboard panels. Lastly, the team

determined that the rigid restraint from intersecting walls appeared to significantly increase lateral

strength and stiffness of the walls.

2.5 Exterior Walls by Arnold et al. (2003)

As part of the CUREE Earthquake Damage Assessment and Repair Project (EDA),

funded by the California Earthquake Authority (CEA), Arnold et al. researched the response of

typically constructed wood-frame walls on the first floor of two story buildings. The objective of

the research was to determine and document the behaviors of walls based on the visible condition

of the finishes, document the typical patterns to walls with openings, and determine the visual and

structural performance of repair methods.

The research consisted of two 8-foot tall by 16-foot long wall configurations with

openings made from 2 in. by 4 in. nominal dimension framing lumber. The construction framing

17

of the two geometries of specimens are shown in Figure 2.3. The interior face each specimen was

sheathed with 1/2 in. gypsum wallboard. The exterior face of each specimen was sheathed with a

typical 7/8 in. three-coat Portland cement plaster system (stucco) applied over an open frame.

Figure 2.4 shows the typical cross section for a specimen installed in the test frame.

The results of the first two specimens of the project were used to determine important

performance regimes and damage states for purposes of repair and assessment of the later

specimens. Five regimes of behavior were established consisting of 0-0.2% drift, 0.2-0.4%, 0.4-

0.7%, 0.7% to ultimate strength, and ultimate strength to failure. The next two specimens were

tested to the established drift levels, repaired aesthetically and structurally, and retested to

determine the effects of the repair methods. The results of these tests were used to develop

qualitative and quantitative assessments of a stucco finished wall after an earthquake to assess the

condition of the wall.

The initial wall behavior was characterized by a very stiff, nearly linear elastic response

with minor cracking of finishes. Within the regimes through the ultimate strength, the wall

stiffness began to soften and propagation of the cracks occurred. Following the ultimate strength,

the wall behavior was characterized by significant deterioration of behavior during all cycles,

extensive damages to the finishes, and detachment of the stucco at the sill plate.

2.6 Components of Partition Walls by Swensen et al (2012)

Within the first phase of this research project, Swensen et al. investigated components of

gypsum partition walls to improve the damage resistance of low-rise residential structures during

earthquakes by unifying structural and architectural systems.

To determine the effect of fastening methods upon the behavior of walls, variations of

mechanical fasteners and construction adhesive connecting the gypsum and framing were tested

18

on specimens built using the construction plans in Figure 2.5a. The results of the initial

component tests, illustrated in Figure 2.6, showed that enhanced drywall screws, which featured a

thicker and longer unthreaded shank, increased the strength of wood-framed specimens by about

20% over the conventional coarse threaded drywall screw, but did not increase the initial

stiffness. The tests featuring construction adhesive to install the wallboards showed increases in

the stiffness and strength on both wood- and steel-framed specimens. Lastly, the tests showed

that an installation using a combination of screws and adhesive increased the strength of

specimens even further.

Five tests, featuring 4 ft by 4 ft wood- and steel-framed wall specimens, with the

construction plans shown in Figure 2.5b, confirmed these results. Within these tests, the

enhanced drywall screws showed increases in stiffness and strength by 60% and 20%,

respectively, over the conventional fasteners for the wood-framed wall, as illustrated in Figure

2.7. The specimens featuring adhesive and mechanical fasteners showed the walls to be twice the

strength and two to four times as stiff as the specimens with only conventional fasteners.

Additional tests were performed to determine the stiffness and strength of two different

methods of joining wallboard panels on specimens subjected to shear. The first joining technique

featured a paper joint tape with premixed joint compound. The second technique featured an

enhanced compound, formed by mixing a quick-drying powder compound with water and a liquid

concrete bonding adhesive, with fiberglass tape. The results of these tests showed that using a

fiberglass joint tape and enhanced joint compound provided a joint that was more than 70%

stronger than the joint with a pre-mixed compound and paper tape.

19

2.7 Typical Construction Review

The definition of “typical” light-frame construction varies based on geographical location

of the structure and the engineer/contractor’s preferences. As a result, many texts of standards

and specification provide the minimum requirements and construction guidelines to achieve the

desired performance of the structure. The minimum construction details for this project were

determined through review of the standards and specifications that included the International

Residential Building Code (2009), National Design Specification for Wood Construction

(ANSI/AF&PA NDS-2005, 2005), the sixth edition of the Design of Wood Structures (Breyer et

al. 2007), and the American Iron and Steel Institute Standards including AISI S200, S211, S212,

S213, & S230 (2007). Within this base of knowledge, there are many variations of type and

spacing of the fasteners and framing members that may be used to achieve the desired structure

response. The following sections present the chosen minimum construction details of “typical”

specimens to be used within this project.

2.7.1 Typical wood-frame construction.

The chosen typical framing members for wood-framed construction are nominally 2 in.

by 4 in. members of grade No. 3 or better lumber with the 4 in. dimension oriented to form the

thickness of the wall. The frame consists of a sill plate which connects the wall to the foundation,

studs which are placed vertically at 16 in. on center, and a top plate which connects the wall to

the floor or roof above. Multiple studs are arranged at the ends of walls and intersections to

provide for rigid attachment of interior and exterior finish materials. The typical configurations

suggested by the American Forest & Paper Association (AF&PA) are shown in Figure 2.8

(AF&PA, 2001). To provide overlapping at corners and intersections, the double top plates are

installed. Connections at the ends of the studs to the top or sole plates are made using 2-16d nails

20

at each end. The built up studs and double top plate are connected using 10d nails installed on the

face of the member at 12 in. on center. All nails used for framing are smooth-common nails.

The sill plates are anchored to the foundation with at least ½ in. diameter bolts spaced at

a maximum of 6 ft. on center with a nut and washer on each bolt. For structures with the seismic

design category of D, plate washers, with a minimum size of 0.229 in. by 3 in. by 3 in. in size, are

located between the sill plate and nut.

The most common sheathing for interior walls is gypsum drywall. Therefore, the typical

sheathing chosen for this research is 5/8 in. thick gypsum wallboard installed with 1-5/8 in. long

Type W or S screws with spacing of 7 in. on the edges and 12 in. on intermediate supports.

These wallboard panels typically come in 4 ft by 8 ft, 4 ft by 10 ft, and 4 ft by 12 ft sizes and may

be installed vertically or horizontally.

2.7.2 Typical steel-frame construction.

Cold-formed steel framing members are of similar sizes to those of wood framing and

must be at least 11/4 in. wide in the least dimension and from 0.033 inch (20 gauge) to 0.112 in.

(10 gauge) thick. Interior studs, with dimensions 1-5/8 in. by 3-5/8 in, and track, with dimension

1-1/2 in. by 3-5/8 in., are used for the walls of this research. The frame consists of c-shaped studs

and top and bottom tracks which are connected using connected using two No. 8 screws on each

end of the stud, one per flange. The corner details suggested by the North American Steel

Framing Alliance (NASFA) are shown in Figure 2.9 (NAFSA, 2000).

The bottom tracks of the walls may be anchored to the foundation under the same bolt

size and spacing requirements as the wood-framed specimens. However, to achieve this, NAFSA

suggests that a stud blocking with a minimum length of 6 in. is installed between the washer and

bottom track as shown in Figure 2.10.

21

The gypsum wallboard panels, used for the internal sheathing, are installed using with

No. 6 or larger screws drywall screws at the same spacing as the wood-framed specimens.

22

Table 2.1 Abbreviated test matrix and results for McMullin and Merrick

Test no.

Loading protocol

Wall openings

Top Constraint

Construction Method

Max load per unit length (lb/ft)

2

Monotonic

Door

Free

Floating edge

399

3

Fixed

664

5 634

6 Cyclic

611

7 Free 378

9 Monotonic

Fixed

Top sill fastened

520

10

Door and window

Floating edge

560 11

Cyclic

506

12 612

13 758

23

Figure 2.1 Wood panel wall force-deformation response and associated damage states (van de Lindt, 2004).

Deformation

Vmax 1500 lb

Failure (e.g., uplift failure,

complete separation)

Substantial damage

(e.g., fastener pull-out)

Moderate damage (e.g.,

fastener yielding, bearing,

cracking)

Major damage

(e.g., wall-board

separation

For

ce

24

(a)

(b)

Figure 2.2 Construction framing elevation for specimens (a) type 1 and (b) type 2 of

McMullin and Merrick research.

25

(a)

(b)

Figure 2.3 Construction framing elevation for (a) walls 1 and 3 and (b) walls 2 and 4 of

Arnold et al. research.

26

Figure 2.4 Typical specimen cross-section installed in frame for Arnold et al. research.

27

(a)

(b)

Figure 2.5 Construction framing for (a) fastener and (b) panel tests

of Swensen et al. research.

28

(a)

(b)

Figure 2.6 Monotonic backbone curves for (a) wood-framed specimens and (b) steel-framed specimens of the fastener tests of Swensen et al. research.

0

100

200

300

400

500

600

700

800

900

0 0.02 0.04 0.06 0.08 0.1

Equiv. Load

Per Fastener (lbs)

Displacement (in)

Adhesive + Screws

Adhesive

Coarse Threaded

29

(a)

(b)

Figure 2.7 Cyclic backbone curves for (a) wood-framed specimens and (b) steel-framed specimens of the panel tests of Swensen et al. research.

‐750

‐500

‐250

0

250

500

750

‐2 ‐1 0 1 2

Racking Load

(lbs/ft)

Drift Ratio (%)

Adhesive + Screws

Maxiscrew

Coarse Threaded

30

(a)

(b)


intersections of partition walls of wood-framed structures (ANSI, 2005).

31

(a)

(b)

Figure 2.9 Suggested corner stud assemblies for (a) corners of exterior walls and (b) at the intersections of partition walls of light-gage steel-framed structures (NAFSA, 2000).

32

Figure 2.10 Anchorage requirements for steel-framed specimens (NAFSA, 2000).

33

CHAPTER 3

TESTING PROGRAM

3.1 Introduction

To investigate the seismic performance of enhanced nonstructural partition walls, twenty

test specimens, consisting of sixteen wood-framed walls and four light gage steel-framed walls,

were constructed and tested as a phase of a larger Network for Earthquake Engineering Research

(NEES) project. Later experiments in the project include full-scale, quasi-static room assembly

tests and full-scale shake-table tests. The component experiments described herein were

conducted at California State University, Sacramento, expanding upon preliminary connector and

small-scale studies performed at Stanford University (Swensen et al., 2012).

The twenty test specimens described in this report are representative of partition and

exterior walls in residential construction, constructed to increase the stiffness, strength and

damage resistance of the structure during earthquake-type cyclic loading. Tables 3.1 and 3.2 list

the test variables, and construction details investigated in the study, including construction

adhesive between the frame and sheathing, uplift tie-down details, orthogonal end returns,

framing material, sheathing type, openings, and wall length. The walls were loaded using a

modified CUREE test protocol as illustrated in Table 3.3 and Figure 3.1.

3.2 Test Setup

To simulate the resisting forces that a planar wall would experience in the first floor of a

two story residential building, specimens were installed within a test frame as shown in Figures

3.2 and 3.3. The frame was also designed to prevent out of plane motions at the top and bottom

of each specimen. The bottom of the specimens were attached to an assembly composed of a

W8x48 base beam and HSS 4x7x1/2 members which were anchored to the strong floor of the

34

laboratory. Stiffener plate assemblies, shown in Figure 3.4, were added to the base beam at each

of the tie down locations to simulate the resistance of a concrete foundation to prevent uplift of

the tie down rod. Referring to Figure 3.2, a W8x28 beam was installed on top of the specimen to

transfer the shear forces into the wall and simulate the stiffness of a second-story wall above.

A 220-kip, ±10 in. stroke hydraulic actuator was used to load the specimens. The

actuator was placed vertically and attached to a bell crank composed of two 1.5 in. thick plates.

The bell crank, illustrated in Figure 3.5, allowed the specimen’s force to be applied horizontally

at the top of the wall. A 2 in. thick steel link was used to attach the bell crank to the W8x28

loading beam as shown in Figure 3.6.

Out-of-plane movement was restricted at the top of the specimen with 4 in. x 4 in. square

plates, covered with Teflon and grease, placed on either side of the loading beam web and

secured onto 1 in. diameter pre-tensioned steel rods fixed to the laboratory strong wall as shown

in Figure 3.7. After the specimens were installed in the test rig, approximately 5,000 lbs of

tension was applied to the rods with turnbuckles (Figure 3.7c) and the walls were secured into

place using the square plates to sandwich the loading beam into the correct position.

For all walls, a 2 in. by 12 in. piece of lumber was added to the top plate of the wall to

simulate a ceiling return. As illustrated in Figure 3.8, the top plates and ceiling members of the

specimens were attached to the loading beam with 1/2 in. diameter through bolts in a staggered

pattern at approximately 6 in. o.c. The sill plates of the specimens were attached to the base

beam with 3/4 in. anchor bolts at 16 in. o.c. and uplift constraints that varied in location and size

according to the test parameters as noted in Table 3.2.

35

3.3 Wall Construction Details and Material Properties

3.3.1 Wood Framing

All lumber used for the wood-framed specimens was Douglas Fir No 2 or better. To allow the

walls to handle the expected shear forces, the wood-framed walls were built with double 2x4 top

plates, a 3x4 sill plate, and 2x4 studs spaced at 16 in. on center. For the specimens with door

openings, the headers over the opening were 4x6 members. The framing was constructed using

8d, 16d, and 20d common nails and wood screws as listed in Table 3.4. The details in Figure

3.9a-c show how the ends of the planar walls and corner assemblies were constructed.

The uplift constraints used at the ends of walls and pier segments included Simpson

Strong-tie HDU tie downs, bent Simpson Strong-tie MST straps, and stiffness enhanced tie

downs as listed in Table 3.2. The manufacturer’s reported allowable tension loads for the HDU

tie downs are shown in Table 3.6 along with the required fasteners and wood member

thicknesses.

Lumber was purchased with a specified moisture level of 18%. To determine the

approximate moisture levels of the specimens during the test for the testing environment, the

moisture level of the lumber for Specimen W-STU was tested during the interval between

framing and testing using an Extech Moisture Meter. Figure 3.10 illustrated the decrease in

moisture content during the three weeks after purchase, stabilizing at approximately 10%

moisture after the 23rd day. Using Figure 3.10 in conjunction with the time intervals listed in

Table 3.5 will provide the approximate moisture levels in the lumber at the time of the test.

Liquid Nails Heavy Duty Construction Adhesive was the adhesive used for the wood-

framed specimens. The adhesive of all specimens were given at least 48 hours of cure time to

obtain the manufacturer’s recommended shear strength of listed in Table 3.7.

36

3.3.2 Steel Framing

Using similar construction plans and procedures, the light-gage steel specimens were

constructed with top and bottom plates of 1-1/2 x 3-5/8 x 18 ga. track and 1-5/8 x 3-5/8 x 20 ga.

partition studs at 16 in. o.c. The frames were built using #10x1 in. self-tapping screws as listed in

Table 3.3. The details in Figure 3.9d-e illustrated the construction of the ends of the planar walls

and corner assemblies. Similar to the wood-framed specimens, the uplift constraints at the ends

were the steel-specific Simpson Strong-tie S/HDU tie downs. The manufacturer’s reported

allowable tension loads for the S/HDU tie downs are shown in Table 3.8 along with the required

fasteners and steel member thicknesses.

Loctite PL375 Heavy-Duty Construction Adhesive was used for the steel-framed

specimens. Similar to the wood-framed specimens, the adhesive was given at least 48 hours of

cure time to obtain the manufacturer’s recommended shear strengths listed in Table 3.9.

3.3.3 Sheathing

All specimens were sheathed with 5/8 in. gypsum type X wallboard fastened to the

framing with 1-5/8 in. drywall screws spaced at 7 in. on center on the edges and 12 in. in the

field. The sheathing, 4 ft. by 8 ft. panels, was installed horizontally as shown in Figure 3.10a.

For specimens that were longer than 8 ft, the joints were staggered as shown in Figure 3.10b.

Three of the wood-framed specimens featured an alternate sheathing material representative of an

exterior sheathing. The exterior wallboards of these specimens were installed horizontally with

staggered joints as shown in Figure 3.10c. The first test featured an exterior sheathing of 5/8 in.

DensGlass® fiberglass mat gypsum sheathing installed with the same techniques as the gypsum

wallboards. The second test featured 15/32 in. Structural I Sheathing installed with 10d nails

spaced at 6 in. on center on the edges and 12 in. in the field. The third and final specimen

featured an exterior finish of three-coat-7/8 in. Portland cement plaster over 5/8 in. DensGlass®

37

sheathing. The DensGlass® sheathing of this specimen was installed using the same techniques

as the first exterior specimen. Two layers of Grade D building paper, 17 gage wire lath, #14 x 3-

½ in. screws with ¼ in. rubber washers spaced at 4 in. on center on the edges and 7 in. on center

in the field, were used to install the stucco. The three coats of stucco were applied with a 3/8 in.

thick scratch coat, a 3/8 in. thick brown coat, and a 1/8 in. thick finish coat.

3.4 Test Matrix

Tables 3.1 and 3.2 show the parameters that were varied for each specimen of this

research. Specimens W1 through W11, discussed in Chapter 4, form the interior walls in the

wood-frame suite. The first specimen, W1, was an 8 ft. x 8 ft. planar wall designed using current

construction techniques. The behavior of this specimen was used as the control for the wood-

framed tests. Specimens W2 through W6 represented an iterative test series to determine the

construction details required to improve the performance of the 8 ft. x 8 ft. planar walls. Within

this series, the behavior of each specimen was analyzed and influenced the uplift constraints,

blocking, and other details of the next specimen. The details of specimen W6 were then applied

to specimens W7 and W8, which represented a shorter iterative test series to determine the details

required for 8 ft. x 8 ft. walls with orthogonal returns. The final three interior walls, specimens

W9 through W11, characterized a test series with varying aspect ratios and door openings

constructed with the successful details of specimens W6 and W9.

Specimens S1 through S4, discussed in Chapter 5, represented the steel-framed suite and

determined how the seismically enhanced details determine through the wood-framed tests could

be applied to steel-framed walls. The first specimen, S1, was an 8 ft. x 8 ft. planar wall built

using current construction techniques and acts as the control for this suite of tests. Specimen S2

was built by applying the successful details of specimen W6 to the steel-frame construction

38

techniques. Specimens S3 and S4 were 8 ft. x 8 ft. walls with orthogonal returns built using the

details from specimen W8, with a similar iterative approach to determine the necessary details for

these walls.

Specimens W-DG, W-PLY, and W-STU represented exterior walls in the wood-framed

suite. These specimens feature differing external sheathing materials applied to walls that were

constructed using the details of specimen W8. The DensGlass® wallboard was chosen for

specimens W-DG and W-STU due to the material similarities to the interior gypsum wallboards

and moisture resistant and fire rated properties. On specimen W-STU, three-coat-7/8 in. stucco,

which is a common finish for residential buildings, was installed over the DensGlass® wallboard

to determine which behaviors are caused solely by the finish when installed with the seismically

enhanced details. W-PLY, which featured plywood sheathing, explores the behavior of an

exterior wall built with this commonly used sheathing and the enhanced details of unibody

construction.

3.5 Loading History

An adapted version of the CUREE Simplified Loading History was used for this study.

This type of loading history, which has no trailing cycles, allows for accurate analytical model

calibration following from force-deformation behavior that better illustrates the stiffness and

strength degradation of the specimen. These models will utilize the results from this phase of

testing for the analysis and design of the two-story building of the final phase of this project. The

protocol, shown in Table 3.3 and Figure 3.1, follows from the protocol used to test the 4 ft. x 4 ft.

enhanced panel tests by Swensen et. al., 2012. However, twelve cycles of smaller displacements

were added to the protocol to capture the behavior between 0.05% and 0.1% interstory drift of the

stiffer system.

39

3.6 Instrumentation

Many instruments were used to record the frame and sheathing behaviors of the

specimens during the tests. These instruments included strain gages, linear variable differential

transformers (LVDTs) and string potentiometers, examples of which are shown in Figure 3.12.

The recorded frame behavior included the lateral displacement at the top and bottom of

the wall, uplift of the end studs, out of plane displacements at the top of the wall and axial forces

in the anchor bolts and tie downs. To record the deformation of the sheathing panels relative to

the frame, LVDTs were used to measure the vertical and horizontal displacements of the internal

and external sheathings at the bottom of the wall.

Six strain gages were placed on the faces of the loading link, shown in figure 3.6a, to

measure the lateral force that was applied to the specimen. A calibration test was performed to

determine the exact elastic modulus of the link by recording the strains in each of the six gages as

compression and tension forces up to approximately 20,000 lbs were applied. Using the linear

data between 20,000 lbs tension and 13,000 lbs compression to relate the applied force and

average recorded strain, as shown in Figure 3.13, the equations below were used to determine the

elastic modulus.

121.81 (3.6.1)

30452.5 (3.6.2)

The locations for the instruments that measured the behaviors of the planar wood- and

steel-framed walls (W1-W6 and S1-S2) are illustrated in Figure 3.14 and described in Table 3.10.

Figure 3.15 and Table 3.11 show the locations of the instruments that measured the behavior of

the wood- and steel-framed walls with returns (W7, W8, W10, S3, and S4). The instrument

locations for the wood-framed specimens with returns and door openings (W9 and W11) are

shown in Figure 3.16 and discussed in Table 3.12. Lastly, the instruments measuring the

40

behaviors of the exterior wood-framed walls (W-DG, W-PLY, and W-STU) are detailed in Figure

3.17 and Table 3.13.

The damage progression recorded for each specimen included observations of physical

damage and/or noises which occurred during each experiment. Along with notes, handheld and

mounted cameras were used to record the visual progression of the damage. The still cameras

took pictures at the peak and zero displacements of each cycle during the test and were used to

create time lapse videos of the test at the locations shown in Table 3.14. Different colors of

marker were used to highlight the observed damage of each set of cycles and show how it

propagated throughout the test. An example of how the different colors show the damage

propagation through the different sets of cycles is shown in Figure 3.18.

41

Table 3.1 Test matrix

Test

No.

Specimen

Frame Materia

l Return

Adhesive

Joint Detail

Additional Parameter

1, 3, 4

W1

Wood

None

None Enhanced

Joint Compoun

d

2 W2

Yes

5 W3 PCP pads at anchor bolts

6 W4 7 W5 8 W6

Blocking

9 W7

T-Shape

10 W8 11 W9 12 W10 13 W11

14 W-DG Wood L-

Shape Yes Blocking

DensGlass® on exterior

15 S1

Steel None

None None 16 S2

Yes Blocking 17 S3 T-Shape 18 S4

19 W-STU Wood

L-Shape

Yes Blocking

Stucco over DensGlass® on

exterior

20 W-PLY Plywood on

exterior

42

Table 3.2 Test matrix uplift constraints and locations

Specimen Uplift Constraint Location

W1, W2 HDU-5

Ends of Wall W3 HDU-8

W4 Enhanced

W5, W6 HDU-8 + Strap

W7 HDU-8 Ends of Returns

W8, W10 HDU-5 Ends of Returns HDU-8 Ends of Main Wall

W9, W11 HDU-8

East End of Wall East Side of Door

HDU-5 Ends of Returns Strap Both Sides of Door

W-DG, W-PLY, W-STU

HDU-8 Ends of Returns

Ends of Main Wall

S1, S2 S\HDU-6 Ends of Wall

S3, S4 S\HDU-6 Ends of Returns S\HDU-9 Ends of Main Wall

Table 3.3 Loading protocol

Drift Amplitude (%)

No. Cycles

Displacement Rate (in/min)

0.05 6 0.10 0.075 6 0.10 0.1 6 0.10 0.2 6 0.20 0.3 6 0.25 0.4 6 0.50 0.5 6 0.50 0.75 4 0.50 1.0 4 0.75 1.25 4 0.75 1.5 3 1.00 1.75 3 1.00 2.0 3 1.25 2.5 2 1.25

43

Table 3.4 Nail and screw information

Name Diameter

(in.) Length

(in.) Framing Material

Location Used

8d common 0.131 2-1/2

Wood

Built up studs

10d common 0.148 3 Plywood to

framing 16d common 0.162 3-1/2 End nail

20d common 0.192 4 End nail

(bottom sill to stud)

#6 1-5/8 in. coarse drywall screw

0.145 1-5/8 Drywall to framing

Wood-to-wood screw 0.150 3 Built up studs

(corner details) Strap-to-wood screw 0.210 1-5/8 Strap to studs

#14 x 3 in. Hex-washer-head self-

drilling screw 0.210 3-1/2 Lath to framing

#10 1in self tapping screw

0.158 1 Steel

Framing connections

#8 1-5/8 in. self- drilling drywall screw

0.123 1-5/8 Drywall to framing

Table 3.5 Time intervals for lumber and adhesive

Specimen Lumber

Purchased to Framed (days)

Framed to Sheathed

(days)

Adhesive Cure Time (days)

W1 3 16 n/a

W2 1 1 (North Side) 37 (South Side

39 (North Side) 3 (South Side)

W3 3 10 4 W4 4 9 4 W5 12 106 2 W6 12 112 2 W7 12 121 4 W8 12 133 3 W9 12 142 4 W10 12 153 3 W11 12 163 8

W-DG 5 8 5 W-PLY 5 7 (Gypsum) 9 (Gypsum)

44

8 (Plywood) 8 (Plywood)

W-STU 5 92 (Gypsum)

57 (Densglass®) 5 (Gypsum)

40 (Densglass®)

45

Table 3.6 Reported requirements and capacities for Simpson Strong-tie wood tie-downs

Model No.

Fasteners Min. Wood

Member Thickness

(in.)

Allowable Tension Loads (lbs)

Anchor Bolt Dia. (in.)

SDS Screws Douglas Fir Deflection at

Allowable Load (in.)

HDU5-SDS2.5 5/8 14-SDS ¼”x2½” 3 5645 0.115 HDU8-SDS2.5 7/8 20-SDS ¼”x2½” 3 5980 0.084

Table 3.7 Liquid Nails construction adhesive reported shear strength

Cure Time (days)

Shear Strength (psi)

1 225 2 300 7 425

Table 3.8 Reported requirements and capacities for Simpson Strong-tie light-gage steel tie-downs

Model

Fasteners Stud

Member Thickness

Tension Load

Deflection at Load

Anchor Bolt Dia. (in.)

Stud Fastener

s

S/HDU6 5/8 12- #14 2-33 (2-20ga)

8495 0.250

S/HDU9 7/8 18- #14 2-33 (2-20ga)

11125 0.189

Table 3.9 Loctite construction adhesive reported shear strength

Cure Time (days)

Shear Strength (psi)

1 26.3 14 42.3

46

Table 3.10 Instruments for Specimens W1 through W6

Instrument Name Type Function Wall displacement (location

1) D String pot.

Global wall displacement at top of wall (control disp)

Actuator force Load Load cell Force of actuator Wall displacement (location

2) OOPE String pot.

Out of plane displacement of North-East of ceiling

Wall displacement (location 3)

OOPW String pot. Out of plane displacement of South-West of ceiling

Wallboard displacement GH LVDT Horizontal disp. of wallboard Wallboard uplift (location

1) GUE LVDT

Uplift of East side of wallboard

Wallboard uplift (location 2)

GUW LVDT Uplift of West side of wallboard

Stud Uplift (location 1) SUE LVDT Uplift of East king stud Stud Uplift (location 2) SUW LVDT Uplift of West king stud

Anchorage force (location 1)

E1 Strain gage Force at shear anchor









Loading strut gage (location 1)

LS1 Strain gage Strain at face of loading strut











Tie down gage (location 1) TDW1 Strain gage Strain on face of west tie down


47



Tie down gage (location 5) TDE1 Strain gage Strain on face of east tie down




48

Table 3.11 Instruments for specimens W7, W8, and W10


1) D String pot.


Actuator force Load cell Force of actuator Wall displacement (location

2) OOPE String pot.




Wallboard displacement GH LVDT Horizontal disp. of wallboard

Stud Uplift (location 1) SUE LVDT Uplift of East king stud Stud Uplift (location 2) SUW LVDT Uplift of West king stud

Stud Uplift (location 3) SUNE LVDT Uplift of king stud at NE return

Wallboard uplift (location 1) GUE LVDT Uplift of East side of wallboard

Wallboard uplift (location 2) GUW LVDT Uplift of West side of Wallboard

Stud Uplift (location 4) SUSE LVDT Uplift of king stud at SE return

Anchorage force (location 1) E1 Strain gage Force at shear anchor Anchorage force (location 2) E2 Strain gage Force at shear anchor Anchorage force (location 3) E3 Strain gage Force at shear anchor Anchorage force (location 4) E4 Strain gage Force at shear anchor Anchorage force (location 5) E5 Strain gage Force at shear anchor Loading strut gage (location

1) LS1 Strain gage

Strain at face of loading strut











Tie down gage (location 1) TDNE1 Strain gage Strain on face of NE tie down


49



Tie down gage (location 5) TDE1 Strain gage Strain on face of E tie down Tie down gage (location 6) TDE2 Strain gage Strain on face of E tie down Tie down gage (location 7) TDE3 Strain gage Strain on face of E tie down Tie down gage (location 8) TDE4 Strain gage Strain on face of E tie down

Tie down gage (location 9) TDSE1 Strain gage Strain on face of SE tie down




Table 3.12 Instruments for wood-framed specimens with returns

and door openings (W9 and W11)


1) D String pot.


Actuator force Load cell Force of actuator Wall displacement (location

2) OOPE String pot.



OOPW String pot.Out of plane displacement of South-West of ceiling

Wallboard displacement GH LVDT Horizontal disp. of wallboard Stud Uplift (location 1) SUE LVDT Uplift of East king stud Stud Uplift (location 2) SUW LVDT Uplift of West king stud Stud Uplift (location 3) SUNE LVDT Uplift of king stud at NE return


GUE LVDT Uplift of East side of wallboard


GUDE LVDT Uplift of Wallboard of East side of doorway

Stud Uplift (location 4) SUDE LVDT Uplift of king stud at East side of doorway


E1 Strain gage

Force at shear anchor


E2 Strain gage


Anchorage force (location E3 Strain Force at shear anchor

50

3) gage Anchorage force (location

4) E4

Strain gage



E5 Strain gage



LS1 Strain gage



LS2 Strain gage



LS3 Strain gage



LS4 Strain gage



LS5 Strain gage



LS6 Strain gage


Tie down gage (location 1) TDNE1Strain gage

Strain on face of NE tie down







Tie down gage (location 5) TDE1 Strain gage

Strain on face of E tie down







Tie down gage (location 9) TDD1 Strain gage

Strain on face of doorway tie down







Table 3.13 Instruments for exterior specimens (W-DG, W-PLY, and W-STU)

51


1) D String pot.


Exterior wall displacement EH LVDT Horizontal disp. of exterior wall


OOPE String pot. Out of plane displacement of North-East of ceiling



Wallboard displacement GH LVDT Horizontal disp. of wallboard Stud Uplift (location 1) SUE LVDT Uplift of East king stud Stud Uplift (location 2) SUW LVDT Uplift of West king stud

Stud Uplift (location 3) SUNE LVDT Uplift of king stud at NE return


GUE LVDT Uplift of East side of wallboard


GUW LVDT Uplift of West side of wallboard

Exterior wall uplift EUE LVDT Uplift of East side of exterior wall























Tie down gage (location 1) TDNE1 Strain gage Strain on face of tie down

52

Tie down gage (location 2) TDNE2 Strain gage Strain on face of tie down Tie down gage (location 3) TDNE3 Strain gage Strain on face of tie down Tie down gage (location 4) TDNE4 Strain gage Strain on face of tie down Tie down gage (location 5) TDW1 Strain gage Strain on face of tie down Tie down gage (location 6) TDW2 Strain gage Strain on face of tie down Tie down gage (location 7) TDW3 Strain gage Strain on face of tie down Tie down gage (location 8) TDW4 Strain gage Strain on face of tie down Tie down gage (location 9) TDE1 Strain gage Strain on face of tie down Tie down gage (location 10) TDE2 Strain gage Strain on face of tie down Tie down gage (location 11) TDE3 Strain gage Strain on face of tie down Tie down gage (location 12) TDE4 Strain gage Strain on face of tie down

53

Table 3.14 Camera Locations for Time Lapse Videos

Specimen Camera #1 Camera #2 Camera #3 Camera #4

W1 North Face Whole Wall

South Face West Corner

n/a n/a


South Face East Corner

n/a n/a




n/a




n/a




n/a




n/a




East Return East Face

South Corner





South Corner


South Face West Side

Door

South Face East Side

Door

South Face Over Doorway

W10 South Face Whole Wall




South Corner

W11 South Face Whole Wall

South Face West Side

Door

South Face East Side

Door

South Face Over Doorway

W-DG North Face Whole Wall

North Face West Corner

South Face Whole Wall


W-PLY North Face Whole Wall




W-STU North Face Whole Wall




54

Figure 3.1 Loading protocol.

55

Fig

ure

3.2

Tes

t fra

me

com

pone

nt id

enti

fica

tion

and

dim

ensi

ons.

56

(a)

(b)

Figure 3.3 Test frame with (a) 8 ft. specimen and (b) 16 ft. specimen installed.

57

Figure 3.4 Stiffener assemblies on the W8x48 base beam.

58

Figure 3.5 Bell crank used to rotate the forces applied to the specimen.

59

(a)

(b)

Figure 3.6 Loading link (a) as designed in the manufacturing plans and (b) as installed in the test frame.

60

(a)

(b)

(c)

Figure 3.7 Out-of-plane restrictions for top loading beam;

(a) Plan and (b) section view of the beam and (c) Turnbuckles used to pretension rods.

61

/2"x3-5/8 18ga. Track

(a)

(b)

Figure 3.8 Section view of wall in test rig; (a) Wood-framed specimen and (b) steel-framed specimen.

62

(a) (d)

(b) (e)

(c)

Figure 3.9 Corner and end details; End of planar wall: (a) Wood-framed, (d) Steel-framed

T-shape corner assembly: (b) Wood-framed, (e) Steel-framed (c) Wood-framed L-shape corner assembly.

63

(a)

(b)

(c)

Figure 3.10: Wallboard layout for (a) 8 ft. walls, (b) 16 ft. walls, and

(c) Exterior face of 8 ft. external walls.

64

Figure 3.11 Approximate lumber moisture level for wood specimens.

65

(a)

(b)

(c)

Figure 3.12 Samples of instrumentation used to measure frame and wallboard behaviors;

(a) Strain gage on loading link, (b) LVDT measuring stud uplift, and (c) string potentiometer measuring specimen displacement.

66

Figure 3.13 Applied force versus average recorded strain used for link calibration.

67

Figure 3.14 Planar wall instrumentation (W1-W6 and S1-S2).

68

Figure 3.15 Instrumentation for specimens with returns and no openings (W7, W8, W10, S3 and S4).

69

Figure 3.16 Instrumentation for specimens with door openings (W9 and W11).

70

(a)

(b)

Figure 3.17 Exterior wall instrumentation (W-DG, W-PLY, and W-STU); (a) On interior face and (b) on exterior face.

71

Figure 3.18 Example of how damage propagation for each set of cycles is highlighted using different colors.

72

CHAPTER 4

EXPERIMENTAL RESULTS OF CYCLIC TESTED PLANAR WOOD-FRAMED WALLS

4.1 Introduction

This chapter discusses the results of the eleven interior wood-framed planar walls, listed

as W1-W11 in Table 3.1, which will contribute to the lateral force resisting system of residential

buildings built with unibody construction techniques. Within this chapter, the specimen

geometry, construction details, and behavior of each specimen during the 0-0.5% and post 0.5%

interstory drifts will be presented for each wall. The behavior discussion is segmented in this

way due to the context of the overall project methodology to design a limited ductility structure,

with minimal damage during design level earthquake events. Thus, it is valuable to provide a

detailed and separated presentation of the results up to, and including, the point where the

specimens show significant damage and inelastic behavior. For most of the specimens,

significant damage occurred at deformation cycles corresponding to 0.2% and 0.3%interstory

drift with strength loss occurring soon thereafter. However, several specimens exhibited a

somewhat more ductile behavior with a strength capacity near 0.5% drift.

To summarize and compare the effects of the construction details investigated in the test

matrix for the wood-framed walls discussed in Chapter 3, the strength, stiffness, and damage

progression of each specimen are reported. Owing to the inherent nonlinear response of the light-

framed wall specimens, the reported stiffness in Table 4.1 is the secant stiffness calculated with

the maximum forces sustained during the first cycle to +/-0.1% interstory drift. In addition, it

allows for comparison between the specimens discussed in this thesis with the previous phase of

4 ft. x 4 ft. wall panels tested at Stanford University (Swensen et al, 2012). However, it should be

noted that the specimen stiffness at earlier cycles (0.05 and 0.075%) are larger. Also listed in

73

Table 4.1 is the one-sided maximum strength capacity in pounds per linear foot of wall and the

interstory drift cycle at which the force was recorded.

Displacement gages, listed in Chapter 3, are used to measure deformations related to 1)

out-of plane twisting, 2) differential slip between the wood-frame and sheathing in the horizontal

and vertical direction, 3) differential horizontal slip between the bottom sill plate and test rig, and

4) uplift. Additional measurements reported in Appendix A for each specimen include uplift

forces in the tie down units and anchor bolts to gain an understanding of the force path at the base

of each specimen.

4.2 Planar Control Test: W1

Test specimen W1 is representative of current construction techniques and acts as the

control for the wood-frame suite of experiments. Additionally, this wall is comparable to

specimens tested by McMullin and Merrick (2001), discussed in Chapter 2. The specimen was

framed with conventional wood 2x4 studs, 5/8 in. gypsum sheathing and mechanical fasteners as

an 8 ft. x 8 ft. planar wall with no door/window openings. Simpson Strong-Tie HDU5 tie-downs

were installed on the inside face of the studs at the ends of the specimen, tightened with a socket

wrench past manufacturer suggested pretensioned load to approximately 3000 lbs. Referring to

Table 4.2, the anchor bolts, which provided the force path for shear forces between the wall and

the test assembly, were tightened to pretension forces of approximately 3000 lbs. with a socket.

The construction framing for this wall is shown in Figure 4.1.

This specimen geometry and type were repeated in test number W1a, W1b and W1c,

where the repetitions occurred to perfect all aspects of the experimental procedure and test setup.

All three specimens had a similar behavior, up to and including failure. Therefore, the results of

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W1c, which utilized the final test assembly and instrumentation, will be reported as the control

specimen for the wood-framed testing suite.

4.2.1 Summary and overall behavior.

Specimen W1 attained a maximum force capacity of 4760 lb, or 298 lb/ft as listed in

Table 4.1, during the 0.5% interstory drift cycles. The one-sided stiffness of this specimen,

measured at 0.1% interstory drift, was 1361 lb/in/ft. The primary mode of failure for this

specimen was fastener failure at bottom sill plate, which extended upwards such that majority of

the bottom panel fasteners had failed by the 1.0% interstory drift cycles.

The maximum out-of-plane rotation angle of the specimen, as illustrated in Figure 4.2,

was calculated as 0.0015 radians – (ΔEast Pot + ΔWest Pot)/76” – with corresponding displacements

recorded as +0.046” and +0.067” during the 1.0% interstory drift cycles, at the East and West end

of the wall, respectively. This rotation produces a displacement equal to 0.06” and 0.08” at the

East and West ends of the specimen, respectively.

4.2.2 Observed behavior 0-0.5% interstory drift.

The force-deformation behavior of the specimen for the range of cycles up to, and

including, the 0.5% interstory drift is shown in Figure 4.3a. Referring to the figure, the shapes of

the hysteretic loops are indicative of inelastic behavior at deformation magnitudes as small as

0.05% drift cycles. Although no visible damage was apparent, noises began to occur within the

wall during the 0.05% drift cycles. These noises begin as small clicks and progressed into louder

creaks as the first signs of visible damage occurred during the 0.1% interstory drift cycles. This

damage preceded fastener popping, and was characterized by paint flaking at the screw heads

located along the bottom sill plate. An example of this paint cracking at 0.1% is shown in Figure

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4.4a. During the 0.3% interstory drift cycles, the fastener heads became clearly visible and

defined as screw popping, as shown in Figure 4.4b. This occurred along the bottom sill plate to

wallboard connection, as well as multiple edge screws along the height of the end-stud as

illustrated in Figure 4.5a. In the subsequent group of cycles, 0.4%, the fastener row above the sill

plate experienced screw popping. No further screw popping was observed during the 0.5%

interstory drift cycles.

4.2.3 Observed behavior post 0.5% interstory drift.

Referring to Figure 4.6a, which shows the force-deformation behavior of Specimen W1

for the entire test, the strength of the wall reached its maximum capacity during the negative

displacement of the 0.5% interstory drift, but decreased in the positive and negative

displacements of the subsequent cycles. The final damage of this specimen, displayed in Figure

4.5b, consisted of screws popping and/or complete fracture for several screws, which began at the

bottom row of screws and progressed towards the top of the wall as the applied displacements

increased.

After the screws popped/sheared, the wallboards pulled away from the frame and were

able to move separately as demonstrated by the images of the lower east corner of the specimen

presented in Figure 4.7. The left image demonstrates how the wallboards displaced past the end

of the frame when a negative displacement was applied to the specimen. The right image shows

the same corner when a positive displacement is applied to the specimen, where once again the

separation between frame and wallboard allows the panel to displace further than the frame.

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4.3 Planar Wall Tests With Unibody Enhancements: W2 Through W6

Specimens W2 through W6 have a similar framing geometry and construction details to

the W1 specimen, explained previously and shown in Figure 4.1, with the addition of

construction adhesive between the wallboard and framing members. This group of tests

represented an iterative process to improve the strength, stiffness and damage performance of the

8 ft. x 8 ft. planar specimens. These improvements included the use of various uplift constraints,

flexible matting at the anchor bolt connections, and mid-height blocking.

As mentioned previously, walls W2 through W6 featured iterative improvements to the

construction details, which increased the strength by 37% and stiffness by 32% of the planar

walls, between walls W2 and W6. The final unibody enhancements for a planar wall (W6),

improved the strength and stiffness by 110% and 164%, respectively, over the control test (W1).

Figure 4.8 shows the cyclic backbone curves for wall specimens W1 through W6,

generated from the one-sided strength force-deformation response by plotting peaks of leading

cycles for each group. Referring to the figure, note the conventional construction test reached its

largest load at 0.5% interstory drift, while the unibody improvements resulted in a less ductile

response with maximum loads at 0.2-0.4% interstory drift, with the exception of the more flexible

W3 which reached the maximum load at 0.75%. However, following the maximum load, the

effect of the construction adhesive decreases and specimens W2-W6 behave similar to the

traditionally constructed specimen, W1, albeit with a higher residual strength which

asymptotically approaches 175 lb/ft.

In addition to the stiffness and strength, the progression and propagation of damage was

considered for each iteration of improvements. Initially, the inclusion of construction adhesive

causes the wallboards and studs to act as a single unit, but the first set (W2, W3 and W4) of tests

revealed a concentrated tension field location at the horizontal plane between the studs and sill

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plate and failed by the propagation of a crack across the bottom wallboard. Each step of

improvements from W2 to W6, attempted to improve the unity of the wall, redistributing the

location of the weak link in the specimen and thus relocated the primary damage. In the final

iteration (W6), the weak link was the gypsum board such that the mode of failure between the

gypsum infill material and the paper, illustrated by Figure 4.9 where the paper backing remained

attached to the studs while the rest of the gypsum had pulled away. After the sheathing failure at

the edges, the specimen behaves similar to the damage progression described previously for W1,

albeit not a severe due to the presence of the adhesive pockets throughout the specimen still

attached after the initial failure.

4.3.1 W2: Characteristics.

The first iteration of unibody improvements, specimen W2, is identical to the framing

and construction details of W1, discussed previously, in that the wall is 8 ft. x 8 ft. planar, with no

openings and Simpson Strong-Tie HDU5 tie-downs at the inside of the end studs. However,

construction adhesive was used in addition to standard drywall fasteners to attach the wallboard

to the frame. The tie downs and anchor bolts were tightened to approximately 3000 lbs, as listed

in Tables 4.2 and 4.3.

4.3.1.1 W2: Summary and overall behavior.

This specimen attained its maximum force capacity of 7310 lb, or a one-sided strength of

457 lb/ft, during the 0.3% interstory drift. The one-sided stiffness of the specimen, measured at

0.1% interstory drift was 2712 lb/in/ft. The primary failure of the specimen was a crack that

propagated across the wallboard, which separated the main panel from the bottom edge screws.

Following the primary damage, adhesive and fastener failures occurred at the bottom of the wall

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with damages progressing upwards such that approximately half of the screws on the specimen

had failed.

The maximum out-of-plane rotation angle of the specimen, was calculated as 0.0037

radians with corresponding displacements recorded as +0.136” and +0.148” during the 0.3%

interstory drift cycles, at the East and West end of the wall, respectively. This rotation produces a

displacement equal to +0.17” and +0.19” at the East and West end of the specimen, respectively.

4.3.1.2 W2: Observed behavior 0-0.5% interstory drift.

Figure 4.3b shows the force-deformation behavior for the specimen during the initial

range of 0 to 0.5% interstory drift. Compared to the hysteresis loops in Figure 4.3a for specimen

W1 which exhibited inelastic action as early as 0.05%, W2 is shown to be elastic up to, and

including, the 0.1% interstory drift cycles.

Similar to W1, noises from within the wall preceded any visible damage. These noises

were quiet pops at the peak displacements of the 0.075% interstory drift cycles. The initial

visible damage occurred during the 0.2% interstory drift cycles when a crack formed on the

wallboard approximately 3 in. from the bottom of the wall. This crack corresponds with the

horizontal plane between the top of the sill plate and bottom of the studs as shown in Figure 4.10.

During the 0.3% interstory drift cycles, the crack propagated across both sides of the wall and

screws along the bottom edge of the wall popped. Additionally, the maximum strength capacity

of the wall was reached within the 0.3% interstory drift cycles. The opening of the crack that

occurred during the 0.4% cycles coincided with uplift of the end stud. During the 0.5% cycles, the

edge screws on the bottom wall board and first row of screws above the cracked section of the

wall popped, resulting in the damage shown in Figure 4.11a.

Further confirmation of the adhesive failure and crack formation is demonstrated by an

increase in the differential movement of the wallboard uplift and horizontal displacements at the

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bottom of the wall. Analysis of the time displacement plots in Figure 4.12 shows the effect of the

adhesive on the wallboard behavior. Referring to Figure 4.12a, prior to the adhesive failure

during the last cycle of the 0.1% interstory drift, at time 2500 seconds, the horizontal

displacement at the bottom of the wallboard was approximately 4% of the displacement at the top

of the wall, demonstrating that the wallboard was attached to the frame. As the adhesive began to

fail in the 0.2% through 0.4% interstory drift, the horizontal wallboard displacement increased to

51% of the specimen displacement, demonstrating that the bottom of the wallboard began to

move with the top of the wall. Similar effects can be seen when comparing the uplift of the stud

and wallboard in Figure 4.12b before, and after, a time test of 2500 seconds. Prior to 0.2%

interstory drift, the wallboard and studs moved together with uplift values within 5% of each

other. However, the damages sustained through the 0.4% interstory drift caused the differential

wallboard uplift to increase to 53% larger than the differential stud uplift.

4.3.1.3 W2: Observed behavior post 0.5% interstory drift.

The final damages to the specimen, displayed in Figure 4.11b, consisted of approximately

half of the drywall fasteners popping and/or shearing through the 1.0% interstory drift. No

additional damage occurred during the larger drifts. After the crack formed along the top of

bottom sill plate and the adhesive failed, the wallboards behaved similar to the wallboards of the

control test as they pulled away from studs and displace parallel to the applied displacement

similar to the wallboard as shown in Figure 4.10c.


To allow the wall to accommodate rigid body in-plane rotations (i.e., rocking), flexible

matting was added at the anchor bolts of Specimen W3, the second iteration of planar walls with

unibody improvements. Polychloroprene (PCP) pads, often referred to by their patented name

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“neoprene” pads, were installed at the anchor bolts between the washer plate and sill plate, as

shown in Figure 4.13. To ensure the pads were not compressed before the test began and to allow

the wall the ability to rotate, the anchor bolts were only tightened to approximately 500 lbs, as

opposed to the 3000 lbs of previous tests. The tie downs located at the inside face of the end

studs, were increased to improve the force transfer of tension from the wall to the test assembly.

The tie downs were tightened with a socket wrench to approximately 3000 lbs.

These adjustments result in an 8 ft. x 8 ft. planar wall, with no openings, Simpson Strong-

Tie HDU8 tie-downs, gypsum wallboard installed with construction adhesive and mechanical

fasteners, and anchor bolts installed with PCP pads.


The wall experienced a maximum force of 7919 lb, or one-sided strength of 495 lb/ft as

listed in Table 4.1, during the 0.75% drift. The one-sided stiffness of the specimen, measured at

the 0.1% interstory drift, was 1856 lb/in/ft, a 32% decrease from specimen W2. The primary

damage for this specimen included cracks in the wallboard at the bottom of the wall and between

the top and bottom panels, similar to those discussed for W2. As a result, adhesive and fastener

failures occurred at the bottom of all panels, and progressed upwards such that the majority of

fasteners on the wall had failed.




displacement equal to -0.18” and +0.10” at the East and West end of the specimen, respectively.

The stiffness and strength of this specimen, while improved from the control test, are

decreased from the results of W2. Furthermore, the cracking and damage that occurred on the top

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panels at lower interstory drift levels is undesirable; therefore none of the remaining tests use

PCP pads.


Similar to the previous tests, noises within the wall began during the early cycles before

visible damage occurred in the 0.2% interstory drift. However, the deformation behavior,

depicted in Figure 4.3c, shows that the specimen began exhibiting inelastic behavior at 0.05%

interstory drift. The first damage presented as a crack that formed 3 in. from the bottom of the

wall. Next, a crack formed along the joint between the top and bottom wallboard panels during

the 0.3% interstory drift cycles. As the width of the crack expanded through subsequent cycles,

the panels no longer moved together as an 8 ft. x 8 ft. unit, allowing equal damage to occur on the

top and bottom panels during the 0.5% interstory drift cycles. The damages that occurred on the

specimen through the 0.5% interstory drift are shown in Figure 4.14a.

Due to the lower clamping forces of the anchor bolts at the sill plate, analog gages

measured sill plate displacements as large as 0.13” in the direction of loading, starting at the 0.2%

interstory drift group of cycles, and continuing through the end of the test. In contrast to

Specimen W2, the horizontal and vertical movements of the wallboard behavior relative to the

framing members is noticeable even at smaller drift levels due to the slip (horizontal) and rocking

(vertical) motion of the specimen from the flexible sill plate condition. Referring to Figure 4.15a,

the horizontal displacement of the wallboard at the bottom of the wall is 30-40% of the applied

specimen displacement at the top of the wall through the 0.5% interstory drift. Similarly, the stud

and wallboard uplift, shown in Figure 4.15b, remain within 75% to 80% of each other.


As a result of the flexible construction details, the strength capacity of the specimen was

delayed until the 0.75% interstory drift, as displayed in Figure 4.6c. Screw popping progressed

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upwards through the larger drifts causing the majority of fasteners connecting to the interior studs

to fail on the top and bottom panels. Additionally, the crack at the bottom of the wall propagated

during these larger displacements, as shown in Figure 4.14b. The stronger tie down may have

affected the shape of this crack which propagated up and around the tie down. Due to an increase

in crack width and the failure of all adhesive and screws within the wallboard section, the lower

East corner of wallboard fell off during the 2.0% interstory drift cycles.


Specimen W4 returns to the construction details and procedures used for W2, with

modifications to address the undesirable damages that occurred on Specimens W2 and W3.

According to the technical specifications for the tie downs used in these tests, the tie downs

exhibit a deflection of approximately 0.1 in. during the maximum load. This deflection may

allow the uplift of the end studs which causes a crack to form in the gypsum wallboard at the

bottom of the wall. To reduce this deformation and provide a higher stiffness to the wall, new tie

downs, shown in Figure 4.16, were manufactured and installed in W4 with similar procedures to

the tie downs of previous tests.

In summary, Specimen W4 is an 8 ft. x 8 ft. planar wall with no openings, with two-sided

gypsum wallboard, construction adhesive and drywall screws, and stiffness enhanced tie downs

on the inside of the end studs. The recorded values of axial pretension in the anchor bolts and tie

downs at the beginning of the test, shown in Tables 4.2 and 4.3, range from 1500 lbs to 2500 lbs.


The stiffness enhanced tie downs proved to be successful for the initial cycles as the

specimen had a one-sided stiffness of 3186 lb/in/ft, an increase of 17% from W2. The wall

experienced a maximum force of 7436 lb, or 465 lb/ft as listed in Table 4.1, during the 0.2%

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interstory drift. The primary failure for this specimen is a crack formed due to the large tension

field action at the base of the wallboard along the top of the sill plate due to uplift of the end

studs. Additionally, fastener failure of five of the six rows of screws on the bottom wallboard

panel occurred.





Separation between the bottom panel and the frame, caused by the aforementioned crack

and fastener failures, allowed for a portion of the wallboard to be removed without affecting the

strength of the wall. This allowed for a better observation of the double end stud and tie-down,

revealing that the eccentricity created by the distance between the tie down to the center of the

end studs allows for a chord rotation of the end stud. This rotation caused uplift at the exterior

edge of the end studs, creating large tensile stresses which fractured the brittle gyp board and led

to crack propagation at the plane of the sill plate.


The first internal noises and damage occurred during the 0.1% interstory drift cycles.

This damage consisted of fastener popping of the majority of screws in the bottom wallboard

panel, as shown in Figure 4.17a. In the next set of cycles (0.2% interstory drift) a crack formed in

the wallboard approximately 3 in. above the bottom of the panel on the East side of the wall.

Additional cracking occurred at the same height across the middle of the wall during the 0.3%

interstory drift cycles. Referring to Figure 4.3d, the force-deformation behavior plot, the strength

capacity of the wall was noticeably diminished in the cycles following these damages. No

additional damage occurred during the 0.4% and 0.5% cycles.

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The graphs of wallboard and frame displacement, in Figure 4.18, emphasize that

wallboard separation began occurring during the 0.2% interstory drift cycles. Within the first

three sets of cycles, 0.05% through 0.1% interstory drift, the wallboard clearly remained attached

to the frame with horizontal displacements at the bottom of the wall less than 0.02 in. and a

vertical displacement that matched the uplift recorded at the studs. However, as the crack formed

across the bottom of the wall, the wallboard behavior changed. The horizontal displacement at

the base of the wallboard increased from 15% of the specimen displacement during the 0.2%

interstory drift cycles, to 59% by the end of the 0.5% cycles. For the same reason, the wallboard

uplift decreased from 80% of the end stud uplift at 0.2% interstory drift to 51% at 0.5% drift.


As displayed in Figure 4.17b, the only damage that occurred during the larger drift cycles

is the buckling of the wallboard located between the cracked sections at the bottom of the wall.

Following the fastener failures and crack propagation during the smaller drift cycles, the

wallboards separated from the frame causing the panels to cease their contributions to the strength

and stiffness of the specimen. A portion of panel was cut away to study the behavior of the frame

and tie down. Figure 4.19, shows the East side of the specimen at peak displacements of positive

and negative drift, suggesting that the external uplift of the stud is caused by rotation of the end

studs due to the eccentricity of the tie down to the center of the end stud. The application of

negative displacements to the wall causes compression in the end studs and no uplift occurs. On

the other hand, positive displacements cause tension in the end studs which causes an uplift of the

studs that the tie-down acts to reduce. As a result of the eccentricity of the tie down to the center

of the studs, uplift is reduced at the inside plane of the end studs but not exterior face, allowing a

rotation of the end studs and a gap to form between the sill plate and stud. This gap causes the

propagation of the crack at the top of the sill plate. While specifically noted within the

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observations of this specimen, this behavior is most likely the cause of the cracking along the sill

plate of the previous specimens (W2 and W3).

During the breakdown of the specimen, it was noted that the adhesive was still pliable;

perhaps suggesting that the amount of adhesive applied is possibly excessive for cure time.


After considering the rotation of the double end-stud, shown in Figure 4.19, and the

undesirable failure mechanism from the horizontal crack at the top of the sill plate, specimen W5

was designed to limit the uplift of the stud on the exterior of the double end-stud. Considering

the limited availability of the stiffness enhanced tie downs, it was determined that, while

improving the specimen stiffness, the new tie downs may present no advantages over the easily

available Simpson Strong-Tie HDU8 tie-downs. Thus, as shown in Figure 4.20, HDU8 tie-downs

were used in conjunction with bent straps on the outside of the end studs, wrapped below the sill

plate. The bottom strap was attached to the bottom of the sill plate with countersunk screws and

to the double end-studs with Simpson lag-bolts. To ensure the strap did not affect the

pretensioning of the tie down, the specimen was installed onto the test rig and the anchor bolts

and tie downs were pretensioned to 2600 to 4200 lbs, prior to attaching the vertical legs of the

bent straps. After the straps were secured onto the end studs, the wallboards were installed in the

same manner as specimens W2 through W4. The pliability of adhesive noted during the tear

down of Specimen W4 was addressed by reducing the amount of adhesive applied to the frame to

a one 3/8 in. bead on each stud and two 3/8 in. beads on the top and bottom plates and exterior

double studs.

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In summary, Specimen W5 is an 8 ft. x 8 ft. planar wall with no openings, gypsum

wallboard installed with construction adhesive and mechanical fasteners, and uplift constraints of

Simpson Strong-tie HDU8 tie-downs and bent straps at the end studs.


Specimen W5 attained a maximum force capacity of 9348 lb, or 584 lb/ft/side as listed in


measured at the 0.1% interstory drift, was 3560 lb/in/ft. The primary mode of failure for this

specimen was the formation of a crack between the panels of wallboard resulting in fastener

failures on the top and bottom panels.


radians with corresponding displacements recorded as -0.062” and -0.100” during the 1.75%


displacement equal to -0.08” and -0.12” at the East and West end of the specimen, respectively.

The bent strap, in conjunction with the tie downs, led to increased stiffness and strength

compared to W2-W4 as the large tension field action, and subsequent crack formation, at the base

of the wall was avoided. However, the failure of the seam between the top and bottom

wallboards led to the eventual adhesive failure at the studs.


The first sign of visual damage occurred during the 0.1% interstory drift cycles as the

mud and paint cracked at the bottom row of screws on each side of the specimen. This behavior

is reinforced by the shape of the force-deformation plots shown in Figure 4.3e, which shows that

the specimen remained relatively elastic and damage-free through the 0.1% displacement cycles.

During the 0.2% interstory drift cycles, screws began popping at the bottom of the wall and a

crack formed at the horizontal joint between top and bottom sheathing boards. The maximum

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strength capacity of the wall was achieved during the 0.4% drift but decreased when additional

screws at the bottom of the wall popped. The increase of the width of the crack between

wallboard panels caused fastener popping at 0.5% interstory drift cycles along the edges of the

top wallboard. An interesting note is that on the North face of the wall, this damage occurred at

the top of the panel and progressed downwards, while on the South face the damage occurred at

the bottom of the panel and progressed upwards. Damages through 0.5% interstory drift are

shown in Figure 4.21a.

Since the damage mostly occurred to the top wallboard, the graphs comparing wallboard

and frame displacements in Figure 4.22 do not provide the similar evidence of adhesive failure of

previously discussed specimens. Instead, Figure 4.22a illustrates that the panel remains secured

to the frame as demonstrated by the relatively small horizontal deformation (less than 0.01”)

recorded at the bottom of the gyp board. While fastener failures have occurred on the bottom

wallboard panel, the panel remains attached to the frame through adhesives or screws which

remained engaged as shown by the wallboard uplift remaining 60-70% of the recorded stud uplift.


As a result of the crack between the wallboards, all further fastener failures, which

occurred during the 0.75% and 1.5% interstory drift cycles, were located on the top panel, as

depicted in Figure 4.21b. Progression of the damage at the top of the wall caused the top panels to

become separated from the frame and appeared to be hazardous should the panels fall off.

The adjustments that were made to the construction procedure for this test, were

successful in improving the performance of a unibody planar wall. The new uplift constraint

assembly successfully prevented the crack at the bottom of the wall. Therefore, the remaining

wood-framed walls with free-standing ends or openings in the direction of the applied

displacement feature this uplift constraint assembly. The second feature of this test is the lesser

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amount of adhesive used for wallboard installation. During specimen tear-down, it was found

that the adhesive developed the full strength of the gyp board as evidenced by residual paper

backing on the studs and top/bottom plates. Thus, all subsequent tests feature 3/8 in. beads of

construction adhesive on the frame.


Specimen W6 is the final iteration of the planar 8 ft. x 8 ft. wall for the wood-framed

suite of tests. Mid-height 2x4 blocking was added between the studs to improve wallboard

behavior by providing four sides of edge screws for each wall panel. Specimens W1 through W5

all featured a joint compound containing a quick-cure concrete substrate to improve the unity of

the horizontal wallboard panels. However, the behavior of specimens W3 and W5 showed that

the shear forces at the panel joints could exceed the strength of the tape and enhanced compound.

With the addition of the blocking, the enhanced joint compound was replaced with an all-purpose,

more traditional, pre-mixed joint compound. While the addition of blocking increases the time

required for construction of the frame, it significantly reduces the time required for the mixing

and application of the quick-cure joint compound while also eliminating the use of a possibly new

material on typical construction sites.

In summary, W6 is an 8 ft. x 8 ft. planar wall with no openings, 2x4 blocking at mid-

height of the frame, gypsum wallboard installed with construction adhesive and mechanical

fasteners, and a tie down assembly of HDU8’s and bent straps on the end studs. The anchor bolts

and tie downs were tightened with a socket wrench to provide axial pretension forces of 1100-

4700 lbs, as listed in Tables 4.2 and 4.3.

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During the 0.3% interstory drift cycles, Specimen W6 attained a maximum force capacity

of 9986 lb, or 624 lb/ft as listed in Table 4.1. The one-sided stiffness of this specimen, measured

at 0.1% interstory drift, was 3589 lb/in/ft. The primary mode of failure for this specimen was

adhesive and fastener failure at bottom sill plate, extending upwards such that majority of the

bottom panel fasteners had failed.





The modifications to the construction procedure used for this specimen resulted in a 32%

increase in stiffness and 37% increase in strength over the first iteration, W2, and 164% and

109%, respectively, over typical construction, W1. The failure of this specimen produces no

cracks within the wallboard and is similar to the typical construction, except that the progression

of damage is delayed and restricted to the bottom wallboard panel.


As illustrated in the force-deformation behavior, shown in Figure 4.3f, the wall remains

elastic through the 0.1% interstory drift cycles. The first inelastic behavior, occurred during the

0.2% cycles, and was accompanied by noises from within the wall. The first visible damage

occurred in the next set of cycles (0.3%) when the bottom edge screws began bulging and the

maximum strength capacity of the wall was achieved. The location of popped fasteners

progressed upwards to include the vertical edges of the bottom gyp panel during the 0.4%

interstory drift and bottom row of interior screws during the 0.5% interstory drift cycles. The

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locations of all of the popped screws during the range of 0-0.5% interstory drift are shown in

Figure 4.23a.

The time-history graphs in Figure 4.24 show the recorded wallboard and frame

displacement through the 0.5% interstory drift and provide confirmation that the adhesive

successfully attaches the wallboard to the frame and that separation began to occur during the

0.2% interstory drift cycles. Prior to failure, the horizontal wallboard displacements suggest that

the panel was firmly attached to the frame with displacements of less than 0.007 in. and an uplift

that was 91-95% of the recorded stud uplift. After separation, the horizontal displacement

increased to 34% of the specimen displacement and the uplift reduced to 88% similarity. At the

end of the 0.5% cycles, the horizontal wallboard displacement had increased to 74% and the

uplift had reduced to 52% similarity.


During the 0.75% interstory drift cycles, the field screws in the third and fourth rows of

the bottom panel popped as shown in Figure 4.4b. No additional damage occurred to the

specimen during the larger displacements. The addition of blocking at the mid-height of this

specimen proved to be successful as the detail prevented a crack from forming on the face or at

the joints of the gypsum wallboard during the test with damages limited to the bottom wallboard

panels.

4.4 Planar Wall Tests With End Returns and Unibody Enhancements: W7 And W8

To examine the interaction between a planar wall in the direction of an applied

displacement and orthogonal walls in a unibody system, five walls were tested with 4 ft. T-shaped

return walls. The first two of these walls featured 8 ft. x 8 ft. shear walls with no openings.

Similar to the process used for specimens W2 through W6, improvements were made to the

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construction techniques of the second test to increase the stiffness, strength, and damageability

performance. These walls use the features of the previously described W6 adjusted to reflect the

addition of orthogonal walls using the details of returns and corners as previously discussed in

Chapter 3. The construction plans for these specimens are shown in Figure 4.25.

With details that allow for a continuous load path between the planar and orthogonal

walls, the stiffness and strength values for W8 listed in Table 4.1 increased by 54% and 16%,

respectively, as compared to the planar W6 specimen. The cyclic backbone curves of specimens

W7 and W8, illustrated in Figure 4.26, show that in addition to the increase in stiffness and

strength, the walls with returns retain a higher residual strength value than the free-standing walls,

ranging between 300 lb/ft and 530 lb/ft after the peak strength. Comparisons of the force

deformation plots for these two specimens, Figures 4.3f and 4.41b, illustrate that the attached

walls also improve the elastic behavior and ductility of the specimen.

A notable difference in the damageability characteristics of the specimens with return

walls is vertical cracking in the compound between the planar and return wall, as well as buckling

at the bottom corner of the planar wall. Referring to the later damage state, after the planar gyp

board separated from the frame, and unlike the wallboards of W1 through W6 which were

uninhibited from sliding, the wallboards in W7 and W8 bear against the return walls and buckle

at large interstory drift excursions, beginning at 0.75%.


Specimen W7 was the first wall to feature the orthogonal returns with an 8 ft. x 8 ft.

planar wall with no openings and 4 ft. return walls at each end. The wall featured gypsum

wallboard installed with construction adhesive and mechanical fasteners, mid-height blocking on

the framing, and Simpson Strong-tie HDU8 tie-downs at the ends of each return wall. By placing

92

the tie downs at the ends of the returns, and not at the ends of the main wall, the test investigates

if the forces developed within the walls could be transferred around the T-joint or if an additional

tie down would be required at the end of each main wall. For this specimen, the axial pretension

in the anchor bolts and tie downs at the beginning of the test ranged from 4000 lbs to 13000 lbs,

as depicted in Tables 4.2 and 4.3.


The maximum force capacity of this specimen was achieved during the 0.4% interstory

drift cycles at 8411 lbs, or 526 lb/ft as listed in Table 4.1. The one-sided stiffness of this

specimen, measured at 0.1% interstory drift, was 3795 lb/in/ft. Similar to previous tests, the

primary mode of failure was fastener and adhesive failures at the bottom sill plate, which

extended upwards such that half of the screws connecting the bottom wallboard panels to the

interior studs had failed. Interaction between the main and return walls resulted in a crack at the

joint between walls, the failure of the majority of vertical edge screws, and bucking of the bottom

corners of wallboard. During tear-down of the specimen, the connection at the T-joint between

the planar wall and orthogonal end returns had failed, significantly bending the 16d nails (12 in.

o.c.) used to join the 2x4 studs of the adjoining wall sections. This failure is shown in Figure

4.27d.





While the performance of this wall is better than the control specimen (W1), the strength,

stiffness, and elastic behavior decreased as compared to W6.

93


The force-deformation behavior plot in Figure 4.28a shows that the specimen began

exhibiting inelastic behavior during the initial, 0.05% interstory drift, cycles. This behavior

increased in the 0.2% cycles, as the first visible damage appeared as a hairline crack at the joint

between the main and return walls (Figure 4.27a). Then, as shown in Figure 4.29a, the fasteners

at the bottom edge of the wall popped in the 0.3% and 0.4% interstory drift cycles. The

maximum capacity was reached during the 0.4% cycles and is decreased in all subsequent cycles.

The wallboard and frame displacement graphs in Figure 4.30 show that the addition of

return walls do little to influence the relative horizontal movement between the sheathing material

and the frame. Compared to similar plots from W6, for example, the horizontal movement of the

sheathing is shown to increase when the adhesive fails at a specimen interstory drift of about

0.2%. Furthermore, the vertical motion of the end stud and wallboard uplift are identical to

adhesive failure (at a test time of approximately 3000 seconds). However, unlike the planar-only

wall specimens where the stud would lift more than the gyp sheathing, the returns tend to have

the effect of decreasing the stud uplift relative to the vertical wallboard motion.


The damages that occurred within the smaller displacements progressed upwards during

the larger drift cycles. Fastener popping included the bottom edge screws and approximately half

of the screws connecting the interior studs and bottom wallboard panels. The cracks at the corner

joints grew throughout the larger displacements causing the vertical edge screws to pop.

The return wall interrupted the established behavior of the wallboard after separation in

which the board slides past the edge of the frame during the larger displacements. This caused

the lower corners of wallboard to buckle during the 0.75% and 1.25% interstory drifts, as shown

94

in Figure 4.27b. Increased damage at the ends of the main wall caused the buckled wallboard to

crumble off, resulting in the shapes shown in Figure 4.29b.

A crack and bulge, displayed in Figure 4.27c, formed on the exterior of the return wall

during the 1.5% interstory drift. Removal of the wallboard after the test’s completion showed

that this damage was caused by failures of the built up corner stud assembly. Figure 4.27d shows

that these failures included both the connections between the studs of the assembly and the

connection between the studs and sill plate.


From the behavior illustrated in specimen W7, seismically enhanced partition walls with

returns require sufficient load-transfer connections at the corner assemblies. In addition, the lack

of tie-downs on the ends of the planar wall were likely to have had a negative effect on the

stiffness and strength characteristics of W7. Therefore, two improvements were made to the

construction details in the construction of Specimen W8. First, to improve the transfer of forces

around T-corners, the fasteners connecting the corner assemblies were changed from 16d nails at

12 in. on center to 3 in. screws spaced at 4 in. on center. Second, HDU8 tie-downs were added at

the ends of the main wall allowing the tie downs at the ends of the returns to be exchanged for

smaller ones.

In summary, Specimen W8 was an 8 ft. x 8 ft. planar wall with no openings with 4 ft.

wide return walls at each end. The frame, which featured mid-height blocking, was sheathed with

gypsum wallboard installed with construction adhesive and mechanical fasteners. The tie downs

of the specimen were Simpson Strong-tie HDU8 tie-downs at the ends of the main wall and

HDU5 tie-downs at the ends of the return walls. The anchor bolts and tie downs began the test

with 5400-11500 lbs of axial pretension.

95


Specimen W8 experienced a maximum force capacity of 11560 lb, or a one-sided

strength capacity of 723 lb/ft, during the 0.4% interstory drift cycles. The one-sided stiffness

measured at the 0.1% interstory drift for this specimen was 5534 lb/in/ft. The primary mode of

failure for this specimen was adhesive failure, followed by fastener failure at the bottom sill plate,

extending upwards such that the majority of fasteners connecting the bottom panel to the interior

studs had failed. The strength, stiffness and elastic behavior of the specimen are improved over

the behaviors of both Specimens W6 and W7.






Referring to Figure 4.28b, which shows the force-deformation behavior for the range of

0-0.5% interstory drift, the specimen retains a generally elastic behavior through the 0.1%

interstory drift. The first visible damage occurred during the 0.1% and 0.2% interstory drift

cycles when hairline cracks formed at the vertical joints between the main and return walls.

Increase elastic behavior, shown in the figure, corresponds to the popping of screws at the bottom

of the wall in the 0.2% and 0.3% cycles. The locations of the damages that occurred on the

specimen during the range of 0-0.5% interstory drift are shown in Figure 4.32a.

A new wallboard to frame behavior is shown by the displacement graphs in Figure 4.33.

Similar to the free-standing unibody walls, the horizontal displacement at the bottom of the wall

remains 0.1 in. or less prior to adhesive failures. Following the failure, the horizontal

displacement increases from 13% to 72% of the applied specimen displacement between the 0.2%

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and 0.5% interstory drift cycles. The difference occurs through the recorded stud and wallboard

uplifts, as the wallboard begins the test with a different amount of uplift than the studs and

becomes more similar through the larger displacements.


The locations of the popped screws progressed upwards during the larger displacements

to include the majority of the screws connecting the bottom wallboard panels to the interior

screws as depicted in Figure 4.32b. Similar to the behavior of specimen W7, the bottom corners

of the wallboard panels began to buckle during the 0.75% interstory drift cycles. However, as a

result of the improved details of the corner assemblies, the corners of this specimen do not

crumble off during the higher drift cycles of the test. Additionally, these details successfully

delayed the crack and bulge on the exterior of the return wall until the 2.0% interstory drift.

Figure 4.34, which was taken after the wallboard was removed after the test’s completion, shows

that the resulting bulge was caused only by failure of the end nailing of the assembly.

4.5 Planar Wall Tests With Openings, Varying Aspect Ratios and Unibody

Enhancements: W9 Through W11

As previously discussed, five wood-framed walls were tested to determine the effects of

orthogonal walls in the unibody system. Walls W7 and W8, discussed above, were 8 ft. x 8 ft.

walls with no openings and T-shaped returns. Specimens W9 through W11 explore the effects of

door openings and differing aspect ratios upon the strength, stiffness, and resulting damages of

the unibody construction.

For the walls with door openings, the strength and stiffness are calculated per foot of full

height wall. Referring to Figure 4.35, which presents the backbone curves for walls W6 and W8

97

through W11, the walls with openings and differing aspect ratios behave similar to W8 in that

after the peak strength is reached, the wall retains a residual strength between 300 and 520 lb/ft.

The one-sided stiffness and maximum strength of all the wood-framed the specimens W9

through W11 can be seen in Table 4.1. The results of Specimen W9 show that stiffness and

strength characteristics of a short wall with a door opening are similar to a free standing wall.

The longer, 16 ft., specimens with returns – even W11 with a door opening – have similar but

improved stiffness and strength characteristics to the square walls with returns. An accurate

curve fit line (R2 = 0.99), shown in Figure 4.36a, captured the ultimate strength capacity, Vmax, of

the experimental specimens well with Vmax = 11.6(H/L)-1.1 where H/L is the aspect ratio of the

wall. Similarly, a linear line captured the stiffness, K,of the specimens with K = -112(H/L)+205.

The damages of the specimens with door openings shows that racking of the wall causes

changes in the angle of the top corners of the door openings, causing cracks to propagate from the

corner of the opening towards the upper corner of the wall.

The differing aspect ratios showed that when the main wall is longer than the length of

wallboard being used, cracks will form at the vertical and horizontal joints around 0.1% to 0.2%

interstory drift. However, since the wallboards all have four sides of edge screws, the width of

the crack only increases to approximately 1/16 in. and does not cause fastener damage around the

locations.


Specimen W9, the first specimen to feature an opening, features a main wall that is 8 ft. x

8 ft. with a 32 in. wide door opening with four foot wide return walls at each end. The

construction plans for this specimen are shown in Figure 4.37. Taking construction details from

Specimen W8, the frame features mid-height blocking, improved corner stud assemblies, and was

98

sheathed with gypsum wallboard installed with construction adhesive and drywall fasteners.

Similarly, Simpson Strong-tie HDU8 tie-downs were installed at the ends of the main wall and

HDU5 tie-downs were installed at the ends of the return walls. Bent straps were installed on the

outside faces of the door opening to prevent the stud uplift and wallboard cracking observed in

the free standing walls. An additional tie down was installed on the inside face of the end stud on

the east side of the doorway which corresponds to the end of the larger pier. To ensure that the

smaller pier had enough anchorage an additional shear bolt was located in the sill plate near the

inside face of the end stud on the West side of the doorway. The anchor bolts and tie downs were

tightened to provide an axial pretension of 1700-2600 lbs as noted in Tables 4.2 and 4.3.

An important note for this specimen is that while this geometry is fairly common in

residential structures, the height to width ratio of the wall piers (2.4 for the large pier and 4.0 for

the small pier) exceed the 2.0 limit for gypsum sheathed shear walls with blocking as set by the

International Residential Building Code (2009). Therefore, according to the current building

standards, walls with this geometry would not be considered to be a part of the lateral force

resisting system.

4.5.1.1 W9: Summary and Overall Behavior.

Specimen W9 attained a maximum force capacity of 7349 lb, or 689 lb/ft as listed in


measured at 0.1% interstory drift, was 3615 lb/in/ft. The primary failure for this specimen

consisted of cracking of the wallboard at the top corners of the door opening extending to the top

corners of the wall. Additionally, fastener and adhesive failures occurred at the vertical edges of

the doorway and bottom edges of the wall biers, and a hairline crack began to form at the joint

between wallboard panels.

99


radians with corresponding displacements recorded as -0.002” and +0.024” during the 0.4%


displacement equal to 0.00” and 0.03” at the East and West end of the specimen, respectively.


Similar to Specimens W6 and W8, this specimen retained a generally elastic behavior

through the 0.1% interstory drift as shown in the force-deformation behavior plot in Figure 4.38a.

The initial damage occurred during the 0.1% interstory drift cycles when hairline cracks formed

at the joints between the main wall and returns. The primary damage began during the 0.2%

interstory drift cycles when cracks formed at the top corners of the doorway as a result of changes

to the angles of the opening during wall racking. During each of the subsequent cycles, through

0.5% interstory drift, these cracks propagated approximately 2 ft. towards the top corners of the

wall where the main and return walls meet the ceiling. Following the damages of the 0.4%

interstory drift cycles, which consisted of crack propagation and the popping of screws at the

bottom of the 40 in. wide pier, the maximum strength capacity of the specimen was reached and

is decreased in all subsequent cycles. The locations of damages through the 0.5% interstory drift

cycles are shown in Figure 4.39a.

The plots of horizontal and vertical displacements of the large pier of the specimen,

presented in Figure 4.40, show that adhesive failures at the beginning of the wall were delayed

until 0.4% interstory drift. Prior to the adhesive failure, the bottom of the wallboard moved less

than 20% of the displacement applied to the top of the wall and maintained an uplift that was 80%

similar to the stud uplift. However, through the progression of adhesive failures in the 0.4% and

0.5% interstory drifts, the horizontal displacement increased to 30% of the applied specimen

displacement and the uplift of the wallboard reduced to 55% similarity of the stud uplift.

100


Propagation of the cracks over the doorway finished during the 0.75% interstory drift

cycles after both cracks had reached the ends of the main wall. The damages that occurred during

the larger drifts include the popping of screws at the bottom of the wall and along the vertical

edges of the doorway. Additionally, hairline cracks began to form at the joint between the top

and bottom wallboard panels as shown in Figure 4.39b.


Specimens W1 through W9 explored the effects of planar wall aspect ratio on the

strength, stiffness and damage states of square walls in the unibody system. Specimen W10

determines how these characteristics change for a long rectangular wall with 4 foot return walls.

The main wall of the specimen is a 16 ft. long wall and 8 ft. tall planar wall with no openings

featuring mid-height blocking, improved corner stud assemblies and gypsum wallboards were

installed upon the wood frame with construction adhesive and mechanical fasteners with

staggered joints. Due to the expected values of tension at the end studs, Simpson Strong-tie

HDU8 tie-downs were installed at the ends of the main and return walls. The construction plans

for this specimen are shown in Figure 4.42. The anchor bolts and tie downs provided a

pretension force of 2000 lbs to 4400 lbs at the beginning of the test.


A maximum force capacity for the specimen W10 of 26060 lb, or 814 lb/ft as listed in

Table 4.1, was attained during the 0.3% interstory drift cycles. The one-sided stiffness of the

specimen, measured at 0.1% interstory drift, was 5426 lb/in/ft. The primary mode of failure for

this specimen was adhesive failure which allowed the horizontal and vertical joints at the edges of

the wall panels to crack. Following the observed behavior of previous specimens, additional

101

failures for this specimen included fastener and adhesive failure along the bottom of the wall and

progressed upwards to include half of the fasteners on the bottom panels.






Figure 4.38b shows the force-deformation behavior for the range of 0-0.5% interstory

drift. The first visible damage occurred during the 0.1% interstory drift cycles when hairline

cracks formed at the vertical joints between wallboards. During the next set of cycles, 0.2%,

hairline cracks also formed at the horizontal joint between wallboards. The joints in the main and

return walls continue to increase through the larger displacements while the joints between the

panels of the main wall only increase to an approximate width of 1/16 in. Though no new visible

damage occurred, the maximum strength capacity of the wall was reached during the first cycles

of the 0.3% interstory drift and decreases in subsequent cycles. The first screws popped at the

bottom edge of the wall during the 0.4% interstory drift cycles and progressed upwards during the

0.5% cycles to include the damages shown in Figure 4.43.

The recorded horizontal displacement at the base of the wallboard sheathing, shown in

Figure 4.44a, provides further confirmation of when the separation of wallboard and frame began

to occur. Prior to the 0.2% cycles, the wallboard displaces less than 0.1 in. Then, corresponding

to the formation of cracks at the wallboard joints during the 0.2% interstory drift, the

displacements increased to 0.2 in. The displacement of the bottom of the wallboard continued to

increase through the larger applied displacements. Following the behavior of Specimen W8, the

102

wallboard uplift prior to adhesive failure is dissimilar to the recorded stud uplift, as shown in

Figure 4.43b. The wallboard uplift continues to increase through the larger displacements.


The locations of the popped screws progressed upwards during the larger displacements

to include approximately half of the screws in the bottom panel as shown in Figure 4.65. Similar

to W8, the disengaged wallboards were unable to displace past the edges of the frame, resulting in

buckling at the bottom corners of wallboard during the 0.75% interstory drift. Additional

buckling occurred at the bottom corners of the interior wallboard panels during the 1.25%

interstory drift.


The third and final wall of the specimens with openings and differing aspect ratios is

Specimen W11 which features a 16 foot long wall with a doorway and 4 foot returns. As shown

in Figure 4.45, this specimen combines the construction details of Specimens W9 and W10. The

frame features mid-height blocking, a 32 in. wide door opening, improved corner assemblies and

gypsum wallboard installed horizontally with construction adhesive and mechanical fasteners.

Uplift constraints for the specimen include Simpson Strong-tie HDU8 tie-downs at the ends of the

main wall and East side of the doorway, which is the end of the large pier, HDU5 tie-downs at the

ends of the return walls, and bent straps on the outside faces of the door opening. The pretension

forces in the anchor bolts and tie downs at the beginning of the test ranged from 550lbs to 2450

lbs, as noted in Tables 4.2 and 4.3.


Specimen W11 experienced a maximum force of 20450 lb during 0.3% drift, equivalent

to a one-sided strength of 767 lb/ft as listed in Table 4.1. The secant stiffness, measured at 0.1%

103

interstory drift, was 4541 lb/in/ft for this specimen. The primary mode of failure for W11

resulted from the combination of adhesive and fastener failures at the bottom of the wall and

cracking at the horizontal and vertical wallboard joints and at the top corners of the door opening.

These failures progressed upwards such that the fastener failures included half of the screws in

the bottom wallboard panels and along the vertical edges of the doorway and the crack above the

doorway had propagated 2 ft. on the smaller pier and 6 in. on the larger pier.






The force-deformation plots for this specimen are shown in Figure 4.38c. The first

visible damage occurred during the 0.075% interstory drift when hairline cracks formed at the

joint between the East end of the main wall and attached return wall. During the 0.2% interstory

drift, when the wall began exhibiting a more inelastic behavior, damages to the wall included

screws popping at the bottom of the wall and the formation of cracks between the wallboard

panels and at the top of the doorway. Similar to W9, the cracks above the doorway propagated

toward the corners during the subsequent applied displacements. However, they did not

propagate as far on the larger pier side, as shown by the damages presented in Figure 4.46.

The observed wallboard uplift and horizontal displacements of the large wall pier, shown

in Figure 4.47, shows that wallboard follows the behavior of previous specimens. Prior to the

0.2% cycles, when the screw popping and crack propagation occurred, the horizontal and vertical

displacements were less than 0.3” and 0.003”, respectively. Following the damages that occurred

104

through the 0.5% interstory drifts, the vertical and horizontal displacements increase to 0.48” and

0.025”, respectively.


Following the behavior of Specimen W9, the damages during the larger displacements

included the propagation of the crack above the doorway, buckling of the bottom corners of the

wall, and the popping of screws along the vertical edges of the doorway. In addition, the wall

follows the behavior of Specimen W10 during the larger displacements through the upwards

progression of popped screws, which include half of the screws in the bottom panels of the larger

pier and the buckling of corners between the interior panels. The one notable difference is that

the joint between the west end of the main wall and the return did not begin to crack until the

0.75% interstory drift cycles. The damages sustained through the end of the test are shown

Figure 4.71.

105

Table 4.1 One-sided stiffness and strength of interior wood-framed wall specimens

Comments Specimen Stiffness (lb/in/ft)

Strength (lb/ft)

Interstory Drift at Max Strength (%)

Current construction (control)

W1 1362 298 0.5

Iterative test series to improve performance of 8 ft. x 8 ft. planar walls with no end returns

W2 2712 457 0.3 W3 1856 495 0.75 W4 3186 465 0.2 W5 3560 584 0.4 W6 3589 624 0.3

Iterative test series on 8 ft. x 8 ft. walls with returns

W7 3795 526 0.4 W8 5534 723 0.2

Test series with varying aspect ratios

W9 3615 689 0.4 W10 5426 814 0.3 W11 4541 767 0.3

*Secant stiffness at 0.1% interstory drift

106

Table 4.2: Anchor bolt pretension forces at beginning of test (lbs)

Anchor Bolt Number 1 2 3 4 5

W1 UNKNOWN (Approx. 3000) W2 UNKNOWN (Approx. 3000) W3 UNKNOWN (Approx. 500) W4 1731 2225 1866 1803 1584 W5 2607 3269 3413 3481 3053 W6 1354 1304 1128 3271 1500 W7 10120 5306 4144 5699 6881 W8 9760 6074 5416 7165 7498 W9 2175 2728 N/A 2564 2155 W10 3051 3491 4404 3915 3424 W11 554 697 552 627 1055

Table 4.3: Tie down pretension forces at beginning of test (lbs)

Tie Down Location

Main Wall:

West Door

Opening: East Main Wall:

East East Return:

North East Return:

South

W1 UNKNOWN

Approx. 3000

N/A

UNKNOWN Approx. 3000

N/A N/A

W2 UNKNOWN

Approx. 3000


W3 UNKNOWN

Approx. 3000


W4 2130 2440 W5 4124 3403 W6 4641 3112 W7

Not Instrumented

Not Instrumented

13110 10420 W8 10930 11470

W9 2097 2307 1767 Not

Instrumented

W10 N/A 2019 3040 2445

W11 796 1164 2441 Not

Instrumented

107

Figure 4.1 South elevation construction framing and details for specimens W1 - W6.

108

(a)

(b)

Figure 4.2 Out-of-plane measurements for specimen W1;

(a) Locations of the measurements and (b) Measured and calculated displacements.

109

(a) W1 (b) W2

(c) W3 (d) W4

(e) W5 (f) W6

Figure 4.3 Force-deformation response for 0-0.5% interstory drift cycles for specimens W1 – W6.

-0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5-5

-4

-3

-2

-1

0

1

2

3

4

Interstory Drift (%)

Ap

plie

d F

orc

e (

kip

s)

-0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5-8

-6

-4

-2

0

2

4

6

8


Ap

plie

d F

orc

e (

kip

s)

-0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5-8

-6

-4

-2

0

2

4

6

8


Ap

plie

d F

orc

e (

kip

s)

-0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5-8

-6

-4

-2

0

2

4

6

8


App

lied

Fo

rce

(kip

s)

-0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5-10.0

-7.5

-5.0

-2.5

0

2.5

5.0

7.5

10.0


Ap

plie

d F

orc

e (k

ips)

-0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5-10.0

-7.5

-5.0

-2.5

0

2.5

5.0

7.5

10.0


Ap

plie

d F

orc

e (

kip

s)

110

(a)

(b)

Figure 4.4 Fastener damage states;

(a) Paint and mud cracking over screw at 0.1% and (b) Popped screw head at 0.3%.

111

(a)

(b)

Figure 4.5 Specimen W1 damage illustration at (a) 0.5% interstory drift and (b) End of test.

112

(a) W1 (b) W2

(c) W3 (d) W4

(e) W5 (f) W6

Figure 4.6 Force-deformation response for 0-2.5% interstory drift cycles for specimens W1 – W6.

-2 -1 0 1 2

-4

-2

0

2

4


Ap

plie

d F

orc

e (

kip

s)

-2 -1 0 1 2-8

-6

-4

-2

0

2

4

6

8


Ap

plie

d F

orc

e (

kip

s)

-2 -1 0 1 2-8

-6

-4

-2

0

2

4

6

8


Ap

plie

d F

orc

e (k

ips)

-2 -1 0 1 2-8

-6

-4

-2

0

2

4

6

8


Ap

plie

d F

orc

e (

kip

s)

-2 -1 0 1 2

-8

-6

-4

-2

0

2

4

6

8

10


Ap

plie

d F

orce

(ki

ps)

-2 -1 0 1 2

-5

0

5

10


Ap

plie

d F

orc

e (

kip

s)

113

(a)

(b)

Figure 4.7 Wallboard separation and sliding in W1 at (a) negative and

(b) positive specimen deformations.

114

Figure 4.8 Cyclic backbone curve comparisons for specimens W1 - W6.

115

(a)

(b)

Figure 4.9 Images demonstrating gypsum wallboard failures as evidenced by residual paper

backing on (a) double end stud and (b) interior stud.

116

(a)

(b)

(c)

Figure 4.10 Images showing damages at bottom of sill plate of W2; (a) Crack and screws popping on South face at 0.3% interstory drift,

(b) Crack location compared to top of sill plate (0.3%), and (c) Wallboard disengaged from studs at 2.0%.

117

(a)

(b)


118

(a)

(b)

Figure 4.12 Displacement time history of wallboard sheathing and frame members for W2 measuring (a) the horizontal displacement at bottom of wallboard

and top of frame and (b) vertical uplift of wallboard and end stud.

0 1000 2000 3000 4000 5000 6000-0.5

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

Time (s)

Dis

pla

cem

en

t (in

)

Bottom Wallboard DisplacementTop Specimen Displacement

0 1000 2000 3000 4000 5000 6000-0.15

-0.1

-0.05

0

0.05

0.1

0.15

0.2

Time (s)

Dis

pla

cem

en

t (in

)

Stud UpliftWallboard Uplift

119

Figure 4.13 Neoprene pads at anchor bolts for specimen W3.

120

(a)

(b)


121

(a)

(b)



0 1000 2000 3000 4000 5000 6000-0.5

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

Time (s)

Dis

pla

cem

en

t (in

)

Horizontal Specimen DisplacementHorizontal Wallboard Displacement

0 1000 2000 3000 4000 5000 6000-0.1

-0.08

-0.06

-0.04

-0.02

0

0.02

0.04

0.06

0.08

Time (s)

Dis

pla

cem

en

t (in

)


122

Figure 4.16 Stiffness enhanced tie down used for specimen W4 prior to installation.

123

(a)

(b)


124

(a)

(b)



0 1000 2000 3000 4000 5000 6000 7000 8000-0.5

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

Time (s)

Dis

pla

cem

en

t (in

)

Wallboard Horizontal DisplacementSpecimen Displacement

0 1000 2000 3000 4000 5000 6000 7000 8000-0.25

-0.2

-0.15

-0.1

-0.05

0

0.05

0.1

Time (s)

Dis

pla

cem

en

t (in

)

Wallboard UpliftStud Uplift

125

(a)

(b)

Figure 4.19 End stud and tie down behavior in W4 at (a) positive and

(b) negative specimen deformations.

126

Figure 4.20 Uplift constraint assembly consisting of tie down and bent strap for W5.

127

(a)

(b)


128

(a)

(b)



0 1000 2000 3000 4000 5000 6000 7000 8000-0.5

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

Time (s)

Dis

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cem

en

t (in

)

Specimen DisplacementWallboard Horizontal Displacement

0 1000 2000 3000 4000 5000 6000 7000 8000-0.04

-0.03

-0.02

-0.01

0

0.01

0.02

0.03

Time (s)

Dis

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t (in

)


129

(a)

(b)


130

(a)

(b)



0 1000 2000 3000 4000 5000 6000-0.5

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

Time (s)

Dis

pla

cem

en

t (in

)

Horizontal Wallboard DisplacementSpecimen Displacement

0 1000 2000 3000 4000 5000 6000-0.1

-0.08

-0.06

-0.04

-0.02

0

0.02

0.04

0.06

0.08

0.1

Time (s)

Dis

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en

t (in

)


131

(a) (b)

(c)

Figure 4.25 Construction framing for Specimens W7 and W8;

(a) East elevation, (b) South elevation, and (c) Plan view.

132

Figure 4.26 Cyclic backbone curve comparisons for specimens W1 and W6 - W8.

133

(a) (b)

(c) (d)

Figure 4.27 Observed damages of specimen W7; (a) Hairline crack formed at corner between main wall and return wall, (b) Buckling of wallboard at corner, (c) Crack on return wall caused by

failure of corner stud assembly, and (d) Failure of stud assembly.

134

(a) W7

(b) W8

Figure 4.28 Force-deformation response for 0-0.5% interstory drift cycles

for specimens W7 – W8.

-0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5-8

-6

-4

-2

0

2

4

6

8


Ap

plie

d F

orc

e (

kip

s)

-0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5-10.0

-7.5

-5.0

-2.5

0

2.5

5.0

7.5

10.0

12.5


Ap

plie

d F

orc

e (

kip

s)

135

(a)

(b)


136

(a)

(b)



0 1000 2000 3000 4000 5000 6000 7000 8000-0.5

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

Time (s)

Dis

pla

cem

en

t (in

)

Specimen DisplacementHorizontal Wallboard Displacement

0 1000 2000 3000 4000 5000 6000 7000 8000-0.04

-0.02

0

0.02

0.04

0.06

0.08

0.1

0.12

Time (s)

Dis

pla

cem

en

t (in

)


137

(a) W7

(b) W8



-2 -1 0 1 2

-8

-6

-4

-2

0

2

4

6

8


Ap

plie

d F

orc

e (

kip

s)

-2 -1 0 1 2-10

-5

0

5

10


Ap

plie

d F

orc

e (

kip

s)

138

(a)

(b)


139

(a)

(b)



0 1000 2000 3000 4000 5000 6000 7000 8000-0.5

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

Time (s)

Dis

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cem

en

t (in

)


0 1000 2000 3000 4000 5000 6000 7000 8000-0.06

-0.04

-0.02

0

0.02

0.04

0.06

Time (s)

Dis

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cem

en

t (in

)


140

Figure 4.34 Improved corner stud assembly failure on specimen W8.

141

Figure 4.35 Cyclic backbone curve comparisons for specimens W6 and W8 – W11.

142

(a)

(b)

Figure 4.36 Curve fits capturing the behavior for varying aspect ratios;

(a) Strength capacity and (b) stiffness.

Vmax = 11.6(H/L)‐1.1

0

5

10

15

20

25

30

0 0.5 1 1.5 2

Strength Cap

acity, V

max(kips)

Aspect Ratio, H/L

W10

W11

W8

W9

LH

k = ‐112(H/L) + 205

0

20

40

60

80

100

120

140

160

0 0.5 1 1.5 2

Stiffness, k (k/in)

Aspect Ratio, H/L

W10

W11

W8

W9

143

(a) (b)

(c)

Figure 4.37 Construction framing for Specimen W9;

(a) East elevation, (b) South elevation, and (c) Plan view.

144

(a) W9

(b) W10

(c) W11



-0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5-8

-6

-4

-2

0

2

4

6

8


Ap

plie

d F

orc

e (k

ips)

-0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5-30

-20

-10

0

10

20

30


Ap

plie

d F

orc

e (

kip

s)

-0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5-20

-15

-10

-5

0

5

10

15

20


Ap

plie

d F

orc

e (

kip

s)

145

(a)

(b)


146

(a)

(b)



0 1000 2000 3000 4000 5000 6000 7000 8000-0.5

-0.4

-0.3

-0.2

-0.1

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0.1

0.2

0.3

0.4

0.5

Time (s)

Dis

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en

t (in

)

Specimen DisplacementHorizontal Wallboard Displacement

0 1000 2000 3000 4000 5000 6000 7000 8000-0.1

-0.08

-0.06

-0.04

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0

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0.06

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Time (s)

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)


147

(a) W9

(b) W10

(c) W11



-2 -1 0 1 2-8

-6

-4

-2

0

2

4

6

8


Ap

plie

d F

orc

e (k

ips)

-2 -1 0 1 2

-20

-10

0

10

20


Ap

plie

d F

orc

e (

kip

s)

-2 -1 0 1 2

-15

-10

-5

0

5

10

15

20


Ap

plie

d F

orc

e (k

ips)

148

Fig

ure

4.42

Sou

th e

leva

tion

con

stru

ctio

n fr

amin

g fo

r S

peci

men

W10

.

149

Fig

ure

4.43

Spe

cim

en W

10 d

amag

e il

lust

rati

on a

t 0.5

% in

ters

tory

dri

ft.

150

(a)

(b)

Figure 4.44 Displacement time history of wallboard sheathing and frame members

for W10 measuring (a) the horizontal displacement at bottom of wallboard and top of frame and (b) vertical uplift of wallboard and end stud.

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000-0.5

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

Time (s)

Dis

pla

cem

en

t (in

)


0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000-0.04

-0.03

-0.02

-0.01

0

0.01

0.02

0.03

0.04

0.05

0.06

Time (s)

Dis

pla

cem

en

t (in

)


151

Fig

ure

4.45

Sou

th e

leva

tion

con

stru

ctio

n fr

amin

g fo

r S

peci

men

W11

.

152

Fig

ure

4.46

Spe

cim

en W

11 d

amag

e il

lust

rati

on a

t 0.5

% in

ters

tory

dri

ft.

153

(a)

(b)


for W11 measuring (a) the horizontal displacement at bottom of wallboard and top of frame and (b) vertical uplift of wallboard and end stud.

0 2000 4000 6000 8000 10000 12000-0.5

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

Time (s)

Dis

pla

cem

en

t (in

)


0 2000 4000 6000 8000 10000 12000-0.06

-0.04

-0.02

0

0.02

0.04

0.06

Time (s)

Dis

pla

cem

en

t (in

)


154

CHAPTER 5

EXPERIMENTAL RESULTS OF CYCLIC TESTED PLANAR STEEL-FRAMED WALLS

5.1 Introduction

This chapter discusses the results of the interior steel-framed planar walls which will

contribute to the lateral force resisting system of residential buildings using unibody construction

techniques. This series consisted of four planar walls with frames made of cold formed light gage

steel, listed as S1-S4 in Table 3.1, which were tested to determine the construction details that

would be suggested for this system.

Similar to the results presented for the interior wood-framed suite, the geometry,

construction details, and behaviors will be presented for each specimen during the 0-0.5% and

post 0.5% interstory drifts. The effects of the construction details are investigated through the

stiffness, strength, and damage progression of each specimen.

The reported stiffness in Table 5.1 is a secant stiffness calculated with the maximum

forces sustained during the first cycle to +/- 0.1% interstory drift. Also listed in Table 5.1 is the

one-sided maximum strength capacity in pounds per linear foot of wall and the interstory drift

cycle at which the force was recorded.

Displacement gages, listed in Chapter 3, are used to measure deformations related to 1)

out-of-plane twisting, 2) differential slip between the wood-frame and sheathing in the horizontal

and vertical direction, 3) differential horizontal slip between the bottom sill plate and test rig, 4)

uplift. Additional measurements reported in Appendix A for each specimen include uplift forces

in the tie down units and anchor bolts to gain an understanding of the force path at the base of

each specimen.

155

5.2 Planar Control Test: S1

Test specimen S1 is representative of the current construction techniques for walls built

with light-gage steel and acts as the control specimen for the steel-frame suite of experiments.

The specimen was an 8 ft. x 8 ft. planar wall with no door/window openings that was framed with

1-5/8 in. x 3-5/8 in. interior cold formed studs with a thickness equivalent to 20 gage, and 1-1/2

in. x 3-5/8 in. cold formed track with a thickness of 18 gage. Both faces of the frame were

sheathed with 5/8 in. thick Type X gypsum wallboards, installed with 1-5/8 in. long drywall

screws. Simpson Strong-tie S\HDU6 tie-downs were installed on the inside web of the king studs

at the ends of the specimen, tightened with a socket wrench to a force of approximately 3200 lbs.

The anchor bolts were tightened to pretension forces which range from 1800 lbs to 2000 lbs. The

construction framing for this wall is shown in Figure 5.1

5.2.1 Summary and overall behavior.

Specimen S1 attained a maximum force capacity of 4259 lbs, or 266 lb/ft as listed in


measured at the 0.1% interstory drift, was 1249 lb/in/ft. The primary mode of failure was

fastener failure at the bottom sill plate, extending upwards such that the majority of the bottom

panel fasteners had failed.





5.2.2 Observed behavior 0-0.5% interstory drift.

The force-deformation behavior plots in Figure 5.2a, shows that the specimen exhibited

inelastic behavior throughout the test. This behavior increased during the 0.2% interstory drift

156

cycles when edge screws along the bottom of the wall popped. These damages progressed

upwards during the 0.4% and 0.5% cycles to include all of the edge screws on the bottom and

East side of the wall, half of the edge screws on the West side of the wall, and half of the interior

screws of the bottom panel as shown in Figure 5.3a.

Figure 5.4 shows how the popped screws of the specimen were identified. As a result of

the wallboard pulling away from the frame and screw, the initial damage appears as a divot in the

wall (Figure 5.4a). Additionally, as shown in the figure, the divot characterizing the location of a

popped screw is not always accompanied by the cracking of the mud and paint covering the

screw. These observed divots are unique to the steel-framed wall because the fine threaded

screws do not withdraw or shear from the studs as occurred in the wood-framed tests. In many

cases however, the visible damage at the popped screws increases to the state shown in Figure

5.4b, where the mud and paint have clearly cracked and the wallboard has become fully

disengaged from the stud.

5.2.3 Observed behavior post 0.5% interstory drift.

The force deformation plot for the entire specimen, shown in Figure 5.5a, gives two

important insights for the response of this specimen to the applied displacements. First, it shows

a notable difference in strength between the positive and negative displacements, which was most

likely caused by the asymmetry of the c-shaped studs. Second, the plot shows that the specimen

achieved its maximum strength capacity during the negative excursion of the 0.75% interstory

drift.

During the larger interstory drift cycles, the locations of visible damages progressed

upwards from the bottom of the wall to include the popping of all of the screws in the bottom

wallboard panels and approximately one third of the screws in the top panels. Similar to the

behavior of the planar wood-framed walls, after the screws failed and the wallboards pulled away

157

from the studs, the wallboards were able to move separately from the studs with the applied

displacements. The locations of the final damages to the wall are shown in Figure 5.3b.

5.3 Planar Wall Tests With Unibody Enhancements: S2 – S4

Three tests were performed that featured unibody enhancements in the steel-framed tests,

consisting of one free-standing wall and two walls that featured T-shaped returns. These

enhancements consisted of the details which produced the best performing wood-framed walls

(W6 and W8) and included the installation of wallboards with construction adhesive and

mechanical fasteners, properly sized tie downs at the ends of wall segments, mid-height blocking

on the frame, and improved built-up stud assemblies at the ends of the wall. Following the

construction techniques for steel-framed walls, the blocking used for these specimens was 1.5 in.

wide, 18 gage cold-formed steel straps installed on the faces of the frame.

As mentioned in Chapter 3, the studs used in this study featured flanges with dimples,

shown in Figure 5.6a, which was intended to improve the bond between the construction adhesive

and framing members. These grooves were proven to be successful when the wallboard was

removed after the completion of a test and the majority of the adhesive remained bonded to the

studs while less adhesive remained on the smooth track, as shown in Figure 5.6b.

Figure 5.7 shows the cyclic backbone curves for all of the steel-framed specimens,

generated from the one-sided strength-deformation response by plotting peaks of leading cycles

for each group. Referring to the figure, note the conventional construction test reached its largest

load in 0.75% interstory drift, while the optimized unibody improvements of specimens S2 and

S4 resulted in a more limited ductility system with its maximum load occurring in the range of

0.3% to 0.4% interstory drift. The adhesive affects the curves by increasing the while reducing

158

the differences of strength between the positive and negative displacements which were observed

on specimen S1.

The unibody enhancements for a free-standing planar wall, featured in specimen S2,

improved the strength and stiffness by 82% and 87%, respectively, over the control test (S1).

Following the maximum load, the effect of the construction adhesive decreases and the specimen

behaved similar to the traditionally constructed specimen by asymptotically approaching a

residual strength value of 60 lb/ft in the “negative” displacement and 130 lb/ft in the “positive”

displacement.

Similar to the results of the wood-framed walls, the stiffness and strength of walls

constructed with unibody enhancements increased further when applied to planar steel-framed

walls with orthogonal end returns. Specimen S4, which featured the optimized construction

procedures for a planar wall with end returns, improved the strength and stiffness by 29% and

74%, respectively, over the unibody planar wall (S2), and by 134% and 225% over the typical

construction (S1). Following the maximum load, the residual strength of the specimen quickly

reduced from 625 lb/ft to approximately 430 lb/ft, before asymptotically approaching a residual

strength value of 230 lb/ft in the “negative” displacement and 315 lb/ft in the “positive”

displacement.

5.3.1 S2: Characteristics.

The first wall which featured the unibody construction techniques, specimen S2, was a

free-standing 8 ft. x 8 ft. planar wall with no openings. This specimen featured Simpson Strong-

tie S\HDU9 tie-downs on the inside web of the king studs, blocking straps at the mid-height of

the frame, and horizontal gypsum wallboards installed with construction adhesive and mechanical

fasteners. The anchor bolts and tie downs were pretensioned to 2500 - 3200 lbs and

approximately 1000 lbs respectively.

159

5.3.1.1 S2: Summary and overall behavior.

Specimen S2 experienced a maximum force capacity of 7736 lb, or a maximum one-

sided strength capacity of 484 lb/ft, during the 0.4% interstory drift cycles. The one-sided

stiffness of the specimen was calculated to be 2332 lb/in/ft during the 0.1% interstory drift. It is

interesting to note that the specimen was weaker and less stiff as compared to its wood-framed

counterpart, W6, which had a one-sided strength and stiffness of 624 lb/ft and 3589 lb/in/ft,

respectively. The primary reason for the difference in performance can be attributed to the weaker

bond between the Loctite adhesive and steel studs, as compared to the stronger Liquid nails and

wood stud bond. The primary damage for this specimen consists of adhesive and mechanical

fastener failures at the bottom sill of the wall.





5.3.1.2 S2: Observed behavior 0-0.5% interstory drift.

The force-deformation behavior for the range of 0 to 0.5% interstory drift of specimen S2

in Figure 5.2b shows that the unibody construction details change the behavior of the specimen in

a few ways. First, the response is relatively elastic behavior through the 0.1% interstory drift,

improving the secant stiffness of the specimen. Second, it reduces the difference in strength

capacity between the positive and negative applied displacements through the 0.5% interstory

drift. And third, the construction details allow the specimen to have an improved strength

capacity.

The first visible damage for the test occurred during the 0.1% interstory drift cycles when

approximately half of the screws connecting the bottom edge of the wallboard and the sill plate

160

popped. This damage was noticeable in the force-deformation response of the specimen through

larger inelastic hysteretic loops after the 0.075% cycle group. Additional damage occurred

during the 0.2% through 0.5% interstory drift cycles as the bottom row of screws connecting to

the studs began to pop. After all of the screws connecting the wallboard to the sill plate had

popped during the 0.4% interstory drift cycles, the strength capacity of the wall decreases. As

shown in Figure 5.8a, the damage of the specimen through the 0.5% interstory drift cycles was

limited to the popping of the screws in approximately the bottom 6 in. of the wall.

The recorded horizontal and vertical displacements of the frame and wallboard, in Figure

5.9, show that the wallboard separation was delayed until 0.2% interstory drift when screws

connected to the studs began to pop. Prior to the separation, the horizontal displacement of the

bottom of the wall was less than 0.015”, but increased from 0.026” to 0.22” during the 0.2%

through 0.5% interstory drift cycles. Similarly, the wallboard had less than 0.015” of uplift

through the 0.1% interstory drift, but increased to 0.08” through the 0.05% interstory drift.

5.3.1.3 S2: Observed behavior post 0.5% interstory drift.

In the larger displacements, the adhesive has failed and the specimen begins acting

similar to Specimen S1 in that the residual strength continues to decrease and shows a difference

between the positive and negative displacements. The visible damage progressed upwards from

the bottom of the wall during the 1.0% and 1.5% interstory drift cycles. However, only half of

the screws in the bottom panel popped as opposed to the majority of all screws on the wall as

occurred in Specimen S1. The locations of all of the damages that appeared on the wall are

displayed in Figure 5.5b.


Specimen S3 is the second steel-framed specimen that featured the unibody

enhancements and the first as such to feature the orthogonal return walls. The main wall of the

161

specimen is an 8 ft. x 8 ft. planar wall with mid-height blocking on the frame, gypsum wallboards

installed with construction adhesive and mechanical fasteners, and Simpson Strong-tie S/HDU9

tie-downs. The return walls are 4 ft. wide returns with S/HDU6 tie-downs at the ends. The

construction framing for this specimen is shown in Figure 5.10. The anchor bolts and tie downs

were maintained pretension force between 1150 lbs and 3100 lbs, as listed in Tables 5.2 and 5.3.


During the 0.75% interstory drift cycles, the specimen achieved a maximum one-sided

strength capacity of 473 lb/ft, or a maximum applied force of 7571 lbs. The one-sided stiffness,

as calculated during the 0.1% interstory drift cycles, was 3202 lb/in/ft. The primary damage

presented by this specimen was adhesive and fastener connection failure at the bottom of the wall

which progressed upwards to include the bottom foot of the wall. Additionally a crack formed at

the joint between wallboard panels, which allowed fastener connection failures around the joint.

While the stiffness of the specimen increases 27% over the free standing wall, the strength

decreased 2%.






The first visible damage occurred during the 0.1% interstory drift cycles, when the cracks

begin forming at the corners between the main and return walls. During the next set of cycles

(0.2%), the screws connecting the bottom of the wallboard to the sill plate and studs popped. A

crack forms at the joint between the top and bottom wallboards during the 0.3% interstory drift

162

cycles. No additional visible damage occurs during the 0.4% and 0.5% cycles. The damage that

occurred through the 0.5% interstory drift is shown in Figure 5.11a.

Referring to Figure 5.2c, which shows the force-deformation behavior of the specimen

for the range of 0-0.5% interstory drift, a local peak strength was achieved during the first cycle

of the 0.1% interstory drifty as the damages of the specimen caused the wall to begin displaying

an inelastic behavior. However, after a decrease in residual strength during the 0.2% cycles, the

strength of the specimen maintained its residual strength of approximately +841lb/ft and -786

lb/ft in the positive and negative displacements, respectively.

The recorded horizontal and vertical displacements of the frame and wallboard, depicted

in Figure 5.12, confirm that wallboard separation began during the 0.2% interstory drift. Prior to

this failure, the wallboard had horizontal and vertical displacements of 0.02” or less, and the

wallboard uplift was similar to the uplift in the studs. In the following cycles through 0.5%

interstory drift, the horizontal displacements increased to 0.17” and the vertical displacements

increased to 0.08”. Additionally, the recorded uplift values show that the corner stud assembly

restricts the movement of the end stud within the specimen.


The true peak strength of the wall was achieved during the 0.75% interstory drift cycles,

as displayed in Figure 5.5c. Similar to the behavior of the wood-framed specimens, the bottom

corners of the main wall began to buckle during the 0.75% interstory drift cycles as a result of

being unable to slide past the frame. The additional damages occurred during the larger interstory

drift, shown in Figure 5.11b, consists of two to three screws popping in the top and bottom

wallboard panels.

163


To improve the behavior of a specimen featuring return walls, including strength,

stiffness, and damage states, improvements were made to the construction procedures for

Specimen S4. To improve the unibody performance, an adjustment was made to the blocking to

prevent out of plane movement of the blocking. A spacer made of stud material was added

between the blocking straps at the ends of the wall, as shown in Figure 5.13. The improved

specimen experienced a strength increase of 29% and stiffness increase of 74% over the unibody

planar wall (S2).

The main wall of specimen S4 is an 8 ft. x 8 ft. planar wall with mid-height blocking on

the frame, gypsum wallboards installed with construction adhesive and mechanical fasteners, and

Simpson Strong-tie S/HDU9 tie-downs. The anchor bolts and tie downs held pretension forces of

approximately 3000 lbs and 2000 lbs, respectively, at the beginning of the test.


Specimen S4 experienced a maximum force of 9996 lbs, or 625 lb/ft as listed in Table

5.3, during the 0.3% interstory drift cycles. The one-sided stiffness for the specimen, as

measured at 0.1% interstory drift, was 4069 lb/in/ft. The primary damage for this specimen was

mechanical fastener and adhesive failure at the bottom of the wall that progressed upwards to

include all of the screws within the bottom foot of the specimen.

The maximum out-of-plane rotation angle of the specimen, was calculated as 4E-5

radians with corresponding displacements recorded as -0.072” and +0.076” during the 2.5%


displacement equal to -0.07” and +0.08” at the East and West end of the specimen, respectively.

164


Figure 5.14a shows the force-deformation behavior of the specimen. The first visible

damage occurred as cracking at the corners between the main and return walls during the 0.2%

interstory drift cycles. Though no new visible damage occurred, the peak strength occurred

during the 0.3% cycles. During the next set of cycles (0.4%) the bottom row of screws,

connecting the wallboard and sill plate, popped. Figure 5.2d shows the damages that occurred on

the specimen through the 0.5% interstory drift.

The recorded horizontal and vertical displacements of the frame and wallboard, shown in

Figure 5.15, confirm that, while no new visible damage occurred, wallboard separation began

during the 0.3% interstory drift cycles. In the first four sets of cycles, 0.05% through 0.2%

interstory drift, the bottom of the wallboard recorded horizontal displacements of less than 0.02”

and uplift similar to the recorded values of the end stud. However, during the 0.3% interstory

drift and later cycles, the horizontal displacement began to increase and the uplift became less

similar.


As expected, the bottom corners of the wall began to buckle during the 0.75% interstory

drift cycles. During the higher interstory drift cycles, the screws which that had visibly popped

progress upwards such that the bottom two rows of screws connecting the wallboard to the

interior studs had popped as shown in Figure 5.14b.

165

Table 5.1 One-sided stiffness and strength of steel walls

Comments Specimen Stiffness (lb/in/ft)

Strength (lb/ft)

Interstory Drift at Max Strength

(%)

Current construction (control)

S1 1249 266 0.75

Planar 8 ft. x 8 ft. wall with no returns

S2 2332 484 0.4

Iterative test series on 8 ft. x 8 ft. walls with returns

S3 3202 473 0.75 S4 4069 625 0.3

*Secant stiffness at 0.1% interstory drift

Table 5.2 Anchor bolt pretension forces at beginning of test (lbs)

Anchor Bolt Number Specimen 1 2 3 4 5

S1 1995 1832 1805 1882 1864 S2 2810 3036 3122 2645 2553 S3 2886 1912 2026 3072 2275 S4 Approximately 3000

Table 5.3 Tie down pretension forces at beginning of test (lbs)

Tie Down Location Specimen West End

Main Wall East End

Main Wall North East End Return

South East End Return

S1 3180 3270 N/A N/A

S2 983 1048 S3 2336 1231 1182 Not

InstrumentedS4 Approximately 2000

166

Figure 5.1 South elevation construction framing and details for specimens S1 and S2.

167

(a) S1

(b) S2

(c) S3 (d) S4

Figure 5.2 Force-deformation response for 0-0.5% interstory drift cycles for S1 – S4.

-0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5

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App

lied

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rce

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Ap

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(a)

(b)

Figure 5.3 Specimen S1 damage illustration at

(a) 0.5% interstory drift and (b) End of test.

169

(a)

(b)

Figure 5.4 Fastener damage states of screws popping showing (a) only a visible divot and (b) cracked mud with screw fully disengaged from wallboard.

170

(a) S1

(b) S2

(c) S3 (d) S4

Figure 5.5 Force-deformation response for 0-2.5% interstory drift cycles for S1 – S4.

-2 -1 0 1 2

-3

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171

(a)

(b)

Figure 5.6 Steel framing chosen to improve unibody enhancements features

(a) grooved flanges of studs improve bonding of construction adhesive as shown when (b) wallboard was removed after test.

172

Figure 5.7 Cyclic backbone curve comparisons for specimens S1 – S4.

173

(a)

(b)



174

(a)

(b)


for S2 measuring (a) the horizontal displacement at bottom of wallboard and top of frame and (b) vertical uplift of wallboard and end stud.

0 1000 2000 3000 4000 5000 6000-0.5

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175

(a) (b)

(c)

Figure 5.10 Construction framing for Specimens S3 and S4 (a) East elevation, (b) South elevation, and (c) Plan view.

176

(a)

(b)



177

(a)

(b)



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178

(a)

(b)

Figure 5.13 Spacers added to blocking of specimen W4; (a) Image of blocking spacer material and

(b) Locations of blocking in plan view of specimen.

179

(a)

(b)



180

(a)

(b)



0 1000 2000 3000 4000 5000 6000-0.5

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181

CHAPTER 6

EXPERIMENTAL RESULTS OF WOOD-FRAMED WALLS WITH EXTERIOR

SHEATHING CONDITIONS

6.1 Introduction

This chapter discusses the results of the exterior wood-framed planar walls built with

unibody construction techniques. This series consists of three planar walls with end returns and

varying exterior sheathing, listed as W-DG, W-PLY, and W-STU in Table 3.1, which were tested

to investigate the effects of applying the unibody construction procedures to an exterior wall.

Similar to Chapters 4 and 5, this chapter will present the specimen characteristics, overall

behavior, and observed behaviors during the 0-0.5% and post 0.5% interstory drift cycles.

6.2 Planar Wall Tests With Unibody Enhancements and Exterior Sheathing

To simulate an exterior wall of a small building, the specimens had an 8 ft. x 8 ft. main

wall with no openings and 2 ft. long orthogonal walls connected in an L-shape at the ends,

creating a large C-shaped specimen as shown in the construction framing plans in Figure 6.1.

The interior of the “C” was sheathed with 5/8 in. Type X gypsum wallboards using the techniques

of the best performing wood-framed interior wall with returns (W8). The exterior sheathing

varied for each test and included fiberglass mat gypsum sheathing wallboards, plywood, and

fiberglass mat gypsum sheathing wallboards plus 7/8 in. three-coat stucco. The details and

procedures for these specimens were influenced by specimen W8 and typical construction

practices for the applicable exterior sheathing materials.

Figure 6.2 illustrates the cyclic backbone curves for the exterior wall specimens,

generated from the force-deformation plots using the peaks of the leading cycle from each group

of displacements. Due to the asymmetry caused by the locations of the return walls, the results of

182

these tests are compared to the best performing interior free-standing wall (W6). The figure

shows that the stiffness of the fiberglass and plywood sheathed specimens was similar to the

stiffness of the interior wall, while the stucco sheathed specimen had an increased stiffness. The

figure also shows that the fiberglass sheathed specimen had a lower strength than the interior wall

while the plywood and stucco sheathed specimens had a higher strength. The recorded two-sided

stiffness and strengths of the specimens, shown in Table 6.1 confirm these visual observations.

6.2.1 W-DG: Characteristics.

The first exterior wall, specimen W-DG, featured 5/8 in. (DensGlass®) fiberglass mat

gypsum sheathing which was chosen to behave similar to the interior gypsum wallboards while

providing additional moisture resistance.

The exterior wallboards were installed using the same adhesive and mechanical fastener

details as the interior specimens. According to typical construction techniques for using this

exterior sheathing material, joint tape and mud specific to the wallboard material would be used

at the horizontal and vertical joints between the wallboard panels. These were not used for the

specimen under the assumption that the wallboards would be used under stucco or an

architectural finish causing the aesthetics of the joints to be unnecessary as they would not be

visible.

In summary, this specimen is an 8 ft. x 8 ft. wall with 2 ft. wide L-shaped returns,

featuring an exterior sheathing of 5/8 in. DensGlass® wallboards and an interior of 5/8 in. gypsum

wallboards installed with construction adhesive and 1-5/8 in. drywall screws. The wood-framing

of this specimen features mid-height blocking and Simpson Strong-tie HDU8 tie-downs at the

ends of the main and return walls. The axial forces in the anchor bolts and tie downs at the

beginning of the test ranged from 3800 lbs to 11540 lbs as listed in Tables 6.2 and 6.3.

183

6.2.1.1 W-DG: Summary and overall behavior.

This specimen attained its maximum force capacity of 8682 lbs, or strength of 1085 lb/ft,

during the 0.4% interstory drift; a 13% decrease when compared to the two-sided strength of W6

– the interior wall specimen with gyp board sheathing. The stiffness of the specimen, measured

at the 0.1% interstory drift, was 7474 lb/in/ft, a 4% increase over the stiffness of the interior wall.

The primary failure of the specimen was adhesive and fastener failures on both faces of the

specimen to include the popping of the bottom screws on both sides of the wall and at the vertical

edges of wallboard on the exterior side.

6.2.1.2 W-DG: Observed behavior 0-0.5% interstory drift.

The force-deformation behavior plot for the specimen, in Figure 6.3a, shows that the

specimen exhibited a relatively elastic behavior through the 0.1% interstory drift. The inelastic

shape of the figure indicates adhesive failures probably began during the 0.2% interstory drift

cycles even through no visible damages occurred. The strength capacity of the specimen

plateaued after the 0.2% drift cycles, which may have been caused by the fibrous material of the

exterior wallboard which extended the ductility of the specimen and allowed the specimen to

maintain the strength capacity. The force-deformation plot for the entire test, in Figure 6.4a,

shows that this plateau continued through the 0.75% interstory drift cycles.

The first visible damage occurred during the 0.075% interstory drift when cracks began

to form on the interior face of the wall at the corners between the main and return walls. Edge

screws at the bottom of both faces of the wall and along the vertical edges of the exterior

wallboards began to pop during the 0.3% interstory drift cycles, as shown in Figure 6.4. In

addition, a crack propagated approximately halfway across the wall at the horizontal joint

between the wallboard panels on the interior face. The crack propagated across three-quarters of

the wall during the 0.4% cycles. The locations of popped screws also progressed upwards during

184

these cycles to include the bottom foot of interior screws on the gypsum side and approximately

half of the interior screws on the larger bottom panel of the DensGlass® side.

Within the 0-0.5% interstory drift cycles, the maximum out-of-plane rotation angle of the

specimen, was calculated as 0.0053 radians with corresponding displacements recorded as -0.27”

and -0.13” during the 0.5% interstory drift cycles, at the East and West end of the wall,

respectively. This rotation produces a displacement equal to -0.31” and -0.19” at the East and

West end of the specimen, respectively.

Figure 6.6 shows the recorded horizontal displacements for the frame and sheathing of

this specimen through the 0.5% interstory drift. The figure confirms that adhesive failures began

during the 0.2% interstory drift cycles (approximately 2800s) on both faces of the wall. Prior to

this failure, the wallboards moved 0.01” or less on both faces. The displacement increased

through the 0.5% interstory drift when both faces moved approximately 0.26”. Through these

graphs, it can be seen that the interior and exterior faces behaved similarly during the test.

However, the larger displacements of the DensGlass® sheathing prior to the 0.2% cycles indicate

that failures may have begun on the exterior face first.

6.2.1.2 W-DG: Observed behavior post 0.5% interstory drift.

As expected, the interior face acted similar to the interior wood-framed walls discussed in

Chapter 4 during the larger interstory drift cycles. This included the buckling of the lower

corners of wallboard and an upwards progression of damages to include half of the screws on the

bottom wallboard as shown in Figure 6.7. No additional damages occurred on the exterior face of

the wall during the larger interstory drift cycles.



185



6.2.2 W-PLY: Characteristics.

The second exterior wall is an 8 ft. x 8 ft. wall with 2 ft. wide L-shaped returns which

features 15/32 in. Structural I plywood on the exterior face and 5/8 in. gypsum wallboards on the

interior face installed with construction adhesive and mechanical fasteners. Guided by typical

construction practices for installing plywood sheathing, the mechanical fasteners were 10d nails

spaced at 6 in. on center along the edges and 12 in. on center in the field. The frame featured

mid-height blocking and Simpson Strong-tie HDU8 tie-downs at the ends of the main and return

walls. At the beginning of the test, the anchor bolts and tie downs contained 1500 lbs to 2600 lbs

of pretension, as listed in Tables 6.2 and 6.3.

6.2.2.1 W-PLY: Summary and overall behavior.

This specimen attained its maximum force capacity of 15120 lbs, or 1890 lb/ft as listed in

Table 6.1, during the 1.0% interstory drift. This strength is 51% higher than the interior planar

wall W6 and 31% higher than W8 - the interior wall with 4 ft. orthogonal end returns. The

stiffness of the specimen, measured at 0.1% interstory drift was 6930 lb/in/ft. This stiffness is 3%

decreased from the stiffness of specimen W8. The primary failure of the specimen was the

adhesive and mechanical fastener failure along the bottom of the gypsum wallboard on the

interior of the wall.

6.2.2.2 W-PLY: Observed behavior 0-0.5% interstory drift.

Similar to the previous specimens, Specimen W-PLY maintained a relatively elastic

behavior through the 0.1% interstory drift as shown in the force-deformation behavior plot in

Figure 6.3b. An increase in the inelastic behavior began during the 0.2% interstory drift cycles

186

when the first visible damage occurred as a crack between the main and return walls on the

interior face of the wall. Fastener failures occurred on the interior face at 0.2% and progressed

upwards along the second interior stud on the East side of the wall during the 0.4% and 0.5%

interstory drift cycles as shown in Figure 6.8. This damage coincided with the vertical joint of

the exterior side. No visible damage occurred on the exterior face of the wall during the 0-0.5%

interstory drift cycles.


specimen, was calculated as 0.0055 radians with corresponding displacements recorded as +0.25”

and +0.17” during the 0.5% interstory drift cycles, at the East and West end of the wall,

respectively. This rotation produces a displacement equal to +0.30” and +0.24” at the East and


Figure 6.9 shows the horizontal displacements for the bottom of the wallboards of both

faces of the wall as compared to the specimen displacement. These graphs illustrate that the

inelastic behavior observed in the force-deformation plot during the 0.2% interstory drift cycles

was caused by adhesive failures on both sides of the wall. Prior to the adhesive failure, the

wallboards moved 0.01” or less. Following the failure, the gypsum wallboard displacement

increased from 0.02” to 0.15” between the 0.2% and 0.5% interstory drift cycles, while the

plywood wallboard displacement only increased from 0.02” to 0.07” within these cycles. This

difference in displacement reflects the observed damages on the interior wallboard while no

damage was observed on the exterior wallboard.

6.2.2.2 W-PLY: Observed behavior post 0.5% interstory drift.

During the higher interstory drift cycles, additional screws popped on the bottom panel of

the interior face of the wall and the bottom corners of the wallboard buckled. Visible damage

187

also occurred on the exterior side after the peak strength occurred when nails began to withdraw

from the wallboard and frame. The final damages to the specimen are shown in Figure 6.10.





6.2.3 W-STU: Characteristics.

Specimen W-STU is the third and final exterior wall specimen. It features exterior

sheathing of 7/8 in. three coat stucco over 5/8 in. DensGlass® wallboard and interior sheathing of

5/8 in. Type X gypsum wallboard.

The construction procedure from W-DG was used for the installation of the frame and

wallboard for this specimen. Then, following the guidelines of typical construction for stucco,

two layers of building paper, and wire lath were installed on the specimen between the wallboard

and stucco. To improve the engagement of the stucco to the frame, 3 in. long #14 hex-washer-

head screws with rubber washers were installed at 4 in. on center along the edges of the wall and

7 in. on center along the studs. The chosen screw and washer combination allowed the wire lath

to sit approximately 1/8 in. away from the wallboard while the top of the screw sat approximately

3/8 in. above the wallboard. Three coats of stucco, consisting of the 3/8 in. thick scratch coat, 3/8

in. thick brown coat and 1/8 in. thick top coat, were then applied, as shown in Figure 6.11. The

scratch and brown coats were given 11 and 9 days, respectively, to cure before the next coat wall

applied. The finishing coat was given 5 days to cure before testing.

In summary, Specimen W-STU is an 8 ft. x 8 ft. wood-framed wall with no openings and

two foot L-shaped returns. The frame featured mid height blocking and Simpson Strong-tie

188

HDU8 tie-downs at the external ends of the main and return walls. The faces of the specimen

feature interior sheathing of gypsum wallboard and exterior sheathing of stucco applied over

DensGlass wallboard. The anchor bolts and tie downs held 780 lbs to 3425 lbs of axial

pretension at the beginning of the test.

6.2.3.1 W-STU: Summary and overall behavior.

This specimen attained its maximum force capacity of 16280 lbs, or 2035 lb/ft, during the

1.0% interstory drift. The stiffness of the specimen, measured at 0.1% interstory drift was 8418

lb/in/ft. The primary failure of the specimen was adhesive and fastener failure at the bottom of

the interior face and cracking at the lower East corner of the exterior face. These damages

progressed upwards during the larger interstory drifts to include damages on the bottom foot of

the interior face and a 45 degree shear crack across the main and East return walls.

6.2.3.2 W-STU: Observed behavior 0-0.5% interstory drift.

Figure 6.3c shows the force-deformation behavior plots for the specimen. The first

visible damage occurred during the 0.2% interstory drift cycles when a hairline crack formed at

the horizontal joint between the top and bottom wallboard panels on the interior face. During the

next set of cycles (0.3%), screws along the bottom edge of the interior face began to pop and

hairline cracks formed at the joints between the main and return walls. On the exterior face, a 4

in. long crack formed at the bottom of the wall along the corner between the main and return wall.

This crack propagated an additional 5 in. during the 0.4% interstory drift cycles. However, even

with these damages, shown in Figure 6.12, the strength of the specimen had not been reached by

the end of the 0.5% interstory drift cycles.

Figure 6.13 shows the horizontal displacement time history for both faces of the wall

during the 0-0.5% interstory drift cycles. Referring to Figure 6.13a, adhesive failure occurs on

the interior face during the 0.2% interstory drift (approximately 3600s). Prior to this failure, the

189

gypsum wallboard moved less than 0.004”. Following the failure, the wallboard displacement

increased to match the recorded displacement of the stucco finish. Between the 0.2% and 0.5%

interstory drifts, the displacement of the sheathing on both faces of the wall increased from 0.03”

to 0.13”.


specimen, was calculated as 0.0077 radians with corresponding displacements recorded as +0.32”

and +0.26” during the 0.5% interstory drift cycles, at the East and West end of the wall,

respectively. This rotation produces a displacement equal to +0.39” and +0.35” at the East and


6.2.3.2 W-STU: Observed behavior post 0.5% interstory drift.

During the larger displacements, the damages at the bottom of the wall progressed

upwards on the interior face to include the typical buckling of the bottom corners of wallboard

and the popping of screws in the bottom foot of the wall as shown in Figure 6.14. On the exterior

face, the crack propagated into a 45 degree shear crack that spanned across the main and East

return wall, as depicted in the figure. A similar crack began forming on the West end of the main

wall but did not finish its propagation before the test was completed. Referring to Figure 6.5c,

which shows the force-deformation response plot, the maximum strength capacity of the

specimen was reached at 1.0% interstory drift.

The asymmetry of the wall geometry and strength in the wall faces caused large out of

plane rotations at the top of the wall which caused cracking at the top of the interior face of the

wall. The test was ended when these forces overcame the out of plane restrictions of the test

assembly during the 1.5% interstory drift cycles.



190



191

Table 6.1: Stiffness and strength of exterior wood-framed walls

Test Name Secant Stiffness

at 0.1% Drift (lb/in/ft)

Strength (lb/ft)

% Interstory Drift Where Max.

Occurred W1

(Typ. Construction)

2724 520 0.5

W6 (Free standing)

7178 1248 0.3

W8 (T-shaped Returns)

11068 1446 0.4

W-DG 7474 1085 0.4 W-PLY 6930 1890 1.0 W-STU 9867 2020 1.0

Table 6.2: Anchor bolt pretension forces at beginning of test (lbs)

Anchor Bolt Number Specimen 1 2 3 4 5

W-DG 10620 4258 3802 6539 5444 W-PLY 2563 1838 2179 2550 2119 W-STU 1966 2128 2519 2213 3421

Table 6.3: Tie down pretension forces at beginning of test (lbs)

Tie down Locations

Specimen East Return North End

Main Wall East End

Main Wall West End

W-DG 11530 9914 9310 W-PLY 1590 2830 2420 W-STU 2086 785 1000

192

(a) (b)

(c)

Figure 6.1 Construction plans for exterior wall specimens featuring (a) the East elevation, (b) the

South elevation, and (c) plan view.

193

Figure 6.2 Cyclic backbone curve comparisons for exterior specimens.

194

(a) W-DG

(b) W-PLY

(c) W-STU


for exterior walls.

-0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5

-8

-4

0

4

8


Ap

plie

d F

orc

e (

kip

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-0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5

-10

-5

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Ap

plie

d F

orc

e (

kip

s)

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-10

-5

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Ap

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orc

e (

kip

s)

195

(a) W-DG

(b) W-PLY

(c) W-STU

Figure 6.4 Force-deformation response for 0-2.5% interstory drift cycles for exterior walls.

-2 -1 0 1 2-10

-5

0

5

10


Ap

plie

d F

orc

e (

kip

s)

-2 -1 0 1 2-15

-10

-5

0

5

10

15


Ap

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orc

e (

kip

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-1.5 -1 -0.5 0 0.5 1 1.5

-15

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-5

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15


Ap

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d F

orc

e (

kip

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196

(a)

(b)

Figure 6.5 Specimen W-DG damage illustration at 0.5% interstory drift on (a) North (Gypsum Wallboard) face and (b) South (DensGlass® Wallboard) face.

197

(a)

(b)

Figure 6.6 Displacement time history of wallboard as compared to the frame for W-DG (a) interior and (b) exterior wallboard horizontal displacements.

0 1000 2000 3000 4000 5000 6000 7000-0.5-0.4-0.3-0.2-0.1

00.10.20.30.40.5

Time (s)

Dis

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t (in

)

Specimen DisplacementGypsum Horizontal Displacement

0 1000 2000 3000 4000 5000 6000 7000-0.5-0.4-0.3-0.2-0.1

00.10.20.30.40.5

Time (s)

Dis

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Specimen DisplacementDensGlass Horizontal Displacement

198

(a)

(b)

Figure 6.7 Specimen W-DG damage illustration at end of test

on (a) North (Gypsum Wallboard) face and (b) South (DensGlass® Wallboard) face.

199

(a)

(b)

Figure 6.8 Specimen W-PLY damage illustration at 0.5% interstory drift on (a) North (Gypsum Wallboard) face and (b) South (Plywood) face.

200

(a)

(b)

Figure 6.9 Displacement time history of wallboard as compared to the frame for D-PLY

(a) interior and (b) exterior wallboard horizontal displacements.

0 1000 2000 3000 4000 5000 6000 7000 8000-0.5-0.4-0.3-0.2-0.1

00.10.20.30.40.5

Dis

pla

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t (in

)


0 1000 2000 3000 4000 5000 6000 7000 8000-0.5-0.4-0.3-0.2-0.1

00.10.20.30.40.5

Ti ( )

Dis

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t (in

)

Specimen DisplacementPlywood Horizontal Displacement

201

(a)

(b)

Figure 6.10 Specimen W-PLY damage illustration at end of test on (a) North (Gypsum Wallboard) face and (b) South (Plywood) face.

202

(a)

(b)

(c) (d) (e) Figure 6.11 Construction of W-STU (a) after Densglass® sheathing is installed,

(b) after building paper and wire lath are installed, (c) after scratch coat, (d) after brown coat, (e) after finish coat.

203

(a)

(b)

Figure 6.12 Specimen W-STU damage illustration at 0.5% interstory drift

on (a) North (Gypsum Wallboard) face and (b) South (Stucco) face.

204

(a)

(b)

Figure 6.13 Displacement time history of wallboard as compared to the frame for

W-STU (a) interior and (b) exterior wallboard horizontal displacements.

0 1000 2000 3000 4000 5000 6000 7000 8000-0.5

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

Time (s)

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0 1000 2000 3000 4000 5000 6000 7000 8000-0.5

-0.4

-0.3

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0

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0.2

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0.4

0.5

Time (s)

Dis

pla

cem

en

t (in

)

Specimen DisplacementStucco Horizontal Displacement

205

(a)

(b)

Figure 6.14 Specimen W-STU damage illustration at end of test on (a) North (Gypsum Wallboard) face and (b) South (Stucco) face.

206

CHAPTER 7

CONCLUSIONS AND FUTURE WORK

7.1 Summary

This thesis summarizes experimental results from twenty light-frame shear wall

specimens tested as part of the first phase of a 3-year NSF (NEES) project to determine the

required construction details to improve the stiffness, strength, and damage resistance of the

components. The specimens are representative of partition walls in residential buildings with

wood or steel studs, spaced at 16 in. on center, and gypsum sheathing to resist lateral loading.

Enhancements had the effect of increasing the stiffness and shear capacity of the specimens, most

notably by using construction adhesive between the studs and sheathing. The seismic

enhancements are part of a proposed design methodology for limited ductility residential

structures in an effort to build more damage resistant homes, reduce expensive repairs and

minimize other negative societal effects of large earthquake events.

The first eleven specimens were representative of interior walls with wood framing

members featuring variations of wall length, openings, and the inclusion of attached orthogonal

walls. The next four specimens tested represented interior walls with light-gage steel frame

featuring full-scale walls with and without attached orthogonal walls. The final three specimens

tested represented exterior wood-framed walls with varying external sheathing.

This chapter summarizes key results from this phase of testing, highlights additional

areas of work to achieve a limited ductility system, and discusses future testing plans of room

assembly tests and a full-scale two-story home at the NEES-Berkeley and San Diego testing

facilities, respectively.

207

7.1.1 Interior Wood-framed Specimens.

Table 7.1 and Figure 7.1a illustrates the stiffness, strength, and damageability results of

the interior wood-framed specimens.

The first specimen, W1, was a planar wall representative of current construction

techniques. The primary mode of failure for this specimen was fastener failure at the bottom sill

plate, which extended upwards such that majority of the bottom panel fasteners had failed. The

specimen achieved a strength of 298 lb/ft and a stiffness of 1362 lb/in/ft.

The unibody modifications to the construction procedure of the specimens – primarily the

addition of construction adhesive between the sheathing and framing members – resulted in a

32% increase in stiffness (3589 lb/in/ft) and 37% increase in strength (624 lb/ft) when compared

to the final test, W6, of an iterative series aimed to improve the racking behavior of an 8 ft. x 8 ft.

specimen. Initial damages to the seismically enhanced specimen, including the primary mode of

failure, were similar to the control specimen (W1), but propagation of the damages were delayed

until larger interstory drift demands.

Orthogonal end returns increased the stiffness by 54% (5534 lb/in/ft) and the strength by

16% (723 lb/ft) when comparing W8 (with returns) to W6 (without returns). The primary mode

of failure for the specimen was adhesive failure, followed by fastener failure at the bottom sill

plate, extending upwards such that the majority of fasteners connecting the bottom panel to the

interior studs had failed. The attached orthogonal wall led to buckling at the bottom corners of

the planar wallboard panels for high deformation levels.

Specimens W9, W10 and W11 investigated the effect of openings and aspect ratios on

the stiffness and strength of the enhanced construction partition walls, as well as the

damageability performance. Referring to Chapter 4, an accurate curve fit line (R2 = 0.99)

captured the ultimate strength capacity, Vmax, of the experimental specimens well with Vmax =

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11.6(H/L)-1.1 where H/L is the aspect ratio of the wall. The damage of the specimens with door

openings showed that racking of the wall causes cracks to propagate from the corner of the

opening towards the upper corners of the wall. The results from the specimens with differing

aspect ratios illustrated that multiple sheathing panels along the length of the wall initiate cracks

at the vertical and horizontal joints around 0.1% to 0.2% interstory drift. However, the width of

the crack only increases to approximately 1/16 in. and does not cause fastener damage around the

locations.

7.1.2 Interior Steel-framed Specimens

Table 7.1 and Figure 7.1b illustrates the stiffness, strength and damageability results of

the interior light-gage steel-framed specimens.

The first specimen tested with steel framing members, S1, was similar to W1 in that

adhesive was not used and the specimen was designed to demonstrate the performance of

common construction practices without seismic enhancements. Similar to the wood-framed

specimens, the primary mode of failure for S1 was fastener failure at the bottom sill plate,

extending upwards such that the majority of the bottom panel fasteners had failed. Referring to

Table 7.1, the maximum stiffness and strength for S1 was 1249 lb/in/ft and 266 lb/ft, respectively.

Referring to Figure 7.2a, while the specimen performs similar to the wood-framed control

specimen, the asymmetry of the c-shaped studs within the frame caused a notable difference in

strength between the positive and negative displacements.

The unibody enhancements for a planar wall, featured in specimen S2, improved the

strength by 82%, by achieving 484 lb/ft, and the stiffness by 87%, with 2332 lb/in/ft, over the

control test, S1. Prior to adhesive failure, the adhesive increased the elastic behavior and strength

capacity of the specimens while reducing the differences of strength between the positive and

209

negative displacements which were observed on specimen S1. Following the maximum load, the

effect of the construction adhesive decreases and the specimen behaved similar to the

traditionally constructed specimen. Interestingly, the specimens with steel framing members had

lowers strength and stiffness capacities as compared to their wood-framed counterparts, as shown

in Figure 7.2b, presumably due to the adhesive de-bonding action between the relatively smooth

steel studs and the gyp board. Thus, unlike the wood-framed specimens, less adhesive was

observed on the metal studs during the post-test inspection.

Similar to the results of the wood-framed walls, the stiffness and strength of walls

constructed with unibody enhancements increased further when applied to planar steel-framed

walls with orthogonal end returns. Specimen S4, which featured the optimized construction

procedures for a planar wall with end returns, improved the strength by 29%, with 625 lb/ft, and

the stiffness by 74%, with 4069 lb/in/ft, over the unibody planar wall. The primary damage for

the specimen was mechanical fastener and adhesive failure at the bottom of the wall that

progressed upwards to include all of the screws within the bottom foot of the specimen.

7.1.3 Exterior Wood-framed Specimens.

Table 7.1 and Figure 7.1c illustrates the stiffness, strength, and damageability results of

the exterior wood-framed specimens.

The first exterior wall, specimen W-DG, featured fiberglass mat gypsum sheathing

installed with the same procedures as the interior gypsum wallboards. This specimen attained a

maximum strength of 1085 lb/ft, a 13% decrease when compared to the planar interior wall W6.

The stiffness of the specimen was 7474 lb/in/ft, a 4% increase over the stiffness of the interior

wall. The primary failure of the specimen was adhesive and fastener failures on both faces of the

210

specimen to include the popping of the bottom screws on both sides of the wall and at the vertical

edges of wallboard on the exterior side.

The second exterior wall, specimen W-PLY, which featured plywood sheathing,

experienced a maximum strength capacity of 1890 lb/ft, which was 51% higher than the free-

standing interior wall, W6, and 31% higher than interior wall with returns, W8. The stiffness of

the specimen, 6930 lb/in/ft, was 3% decreased from the stiffness of Specimen W6. The primary

failure of the specimen was the adhesive and mechanical fastener failure along the bottom of the

gypsum wallboard on the interior of the wall. Visible damage did not occur on the exterior

sheathing until the displacements after the maximum strength capacity was achieved.

The third and final exterior wall specimen, W-STU, featured an exterior sheathing of 7/8

in. thick – three-coat stucco applied over fiberglass mat gypsum sheathing. The specimen

attained a strength capacity of 2020 lb/ft, which was 62% greater than the interior planar

specimen, W6, and a stiffness of 9867 lb/in/ft which was 38% greater. The primary failure of the

specimen was adhesive and fastener failure at the bottom of the interior face and cracking at the

lower East corner of the exterior face. These damages progressed upwards during the larger

interstory drifts to include damages on the bottom foot of the interior face and a 45 degree shear

crack across the main and East return walls.

7.2 Conclusions for Limited Ductility/Unibody Construction Techniques

This research demonstrated that the strength and stiffness of planar light-framed walls

improved through the addition of construction adhesive and other construction details. To ensure

that the primary failure of the wall is adhesive and fastener failure at the bottom of the wall, these

details include blocking at the mid-height of the frame – either with 2x4 blocks or a metal strap –

and properly sized shear and uplift constraints on the ends of the wall. For wood-framed

211

specimens, the uplift constraints should include a tie down on the inside of the end studs and

straps on the outside to prevent chord rotation of the end studs. The stiffness and strength of walls

increase further when attached to intersecting (return) walls. To ensure an efficient transfer of

forces around corners, the wall intersections require corner assembly studs attached with screws

at 4 in. on center and properly sized tie downs at the ends of the main and return walls.

Through these improvements to the construction details commonly used in partition

walls, the interior walls of residences may contribute significant capacity to the lateral force

resisting system. The improved strength and stiffness of these walls will be effective within the

“unibody” construction methodology to decrease the deformation demands, displacement-

sensitive damage and repair cost/time.

However, the new system will present more challenges over typical construction. While

the methodology has been developed using enhanced, inexpensive procedures, these procedures

will increase the costs of materials, labor, and inspection for the construction of residences within

this methodology. For effective implementation of the limited ductility or “unibody” system,

contractors and homeowners will need to be educated on the methodology and buy into the

advantages and limitations of the system.

7.3 Future Work and Recommendations

As discussed in previous chapters, this research is the first phase of a multi-phase project

to develop efficient low-cost construction details to improve the seismic performance of light-

frame residential buildings. The results of this research will influence the geometries and

construction details of three-dimensional room assemblies for the next phase of testing on the

interaction between the shear walls and floor diaphragms. In turn, the results of room tests will

212

influence the design and construction details of the shake table testing of a two-story building in

summer of 2014.

Due to time and funding limitations, several experimental variables were not included in

the testing. These variables include variations of the specimen geometry, investigation of the

long-term effects of the proposed construction details, and the testing of more efficient materials

and procedures for interior and exterior walls. Recommendations for future studies of unibody

planar walls include:

1- Variations of the door and window openings, aspect ratios, and return wall

configurations

2- Exploration of ways to prevent or reduce cracking above openings and at the

wallboard panel joints

3- Investigate more adhesive products for bonding between the wallboards and framing;

including the gypsum wallboard to steel-framing connections and DensGlass® to

wood-framing connections

4- Further investigate construction details for stucco specimens to improve the

efficiency of the construction procedures, including the wire lath and installation

screws

5- Further exploration of the life-cycle benefits of these construction techniques

6- Determination of wall behavior after extended adhesive curing

7- The effects of building settlement on adhesive integrity

8- Determination of wall behavior after repairs have been made; including common

household repairs and repairs following a large seismic event

213

Table 7.1 Summary of interior specimen behaviors

Specimen

Secant Stiffness at 0.1% Drift (lb/in/ft)*

Strength(lb/ft)*

% Interstory Drift at

Maximum Strength

% Interstory Drift at Visible Damage (Type)

W1 Wood, Planar, Typical Const.

1362 298 0.5 0.1 (Screws pop)

W6 Wood, Planar,

Adhesive 3589 624 0.3 0.3 (Screws pop)

W8 Wood, Returns, Adhesive

5534 723 0.2 0.1 (Corner joints crack)

0.2 (Screws pop)

S1 Steel, Planar, Typical Const.

1249 266 0.75 0.2 (Screws pop)

S2 Steel, Planar, Adhesive

2332 484 0.4 0.1 (Screws pop)

S4 Steel,

Returns, Adhesive

4069 625 0.3 0.1 (Corner joints crack)

0.4 (Screws pop)

*Note: 1-sided stiffness and strength

Table 7.2 Summary of exterior specimen behaviors

Specimen

Secant Stiffness at 0.1% Drift

(lb/in/ft)*

Strength(lb/ft)*

% Interstory Drift at

Maximum Strength

% Interstory Drift at Visible Damage (type)

W‐DG DensGlass

® 7474 1085 0.4

0.075 (Crack at corners‐ Int. face)

0.3 (Screws pop‐ Both faces)

W‐PLY Plywood

6930 1890 1.0 0.2 (Crack at corners‐ Int. face)0.3 (Screws pop‐ Int. face) 1.75 (Nails withdraw‐ Ext.

214

face)

W‐STU Stucco + DensGlass

®

9867 2020 1.0

0.2 (Crack at corners‐ Int. face)0.3 (Screws pop‐ Int. face) 0.3 (Crack at corners‐ Ext.

face)

*Note: 2-sided stiffness and strength

215

(a)

(b)

(c) Figure 7.1 Cyclic backbone curves for wood and steel specimens;

(a) Interior wood specimens, (b) interior steel specimens, and (c) exterior wood specimens.

216

(a)

(b)

(c) Figure 7.2 Cyclic backbone curves for interior wood and steel specimens;

(a) Typical construction specimens, (b) planar unibody specimens, and (c) unibody specimens with returns.

217

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APPENDIX A

UPLIFT FORCES RECORDED AT TIE DOWN UNITS AND INSTRUMENTED ANCHOR

BOLTS

This appendix presents results from instrumentation designed to measure uplift forces at

the base of the wall specimens and a discussion for each specimen is included. Tie-down rods

were instrumented by connecting the threaded rods from the HDU brackets into a coupler nut

attached to a steel stub with four uniaxial strain gages on each face of a square cross section. The

stubs were calibrated in a load frame, with the average strain reading providing a relationship to

the axial force. Prefabricated instrumented bolts were purchased from Strainsert and used to

measure the axial force in five anchor bolt locations for each test. While anchor bolts are typically

not designed to resist uplift forces, the sheathing material has sufficient stiffness prior to

separating from the frame to transmit force into the sill plate directly, thereby engaging the

anchor bolts.

Figure A.1 provides illustrative layouts for the uplift instrumentation locations for the

various tested wall geometries. These layouts are referenced in Figure A.2 which summarizes the

results from each specimen. Chapter 3 contains additional details regarding the setup of the uplift

constraints and anchor bolts. The maximum axial forces recorded for the instrumented tie downs

and anchor bolts are shown in Figure A.2 with two plots for each experiment separated by the

range of interstory drifts measurements – (a) 0.05 -- 0.5% and (b) 0.75%, 1.27% and 1.75%. The

forces are measured above the pretension force and shown as a percentage of the specimen’s

corresponding lateral force. The figure also shows the cumulative change of pretension forces

based on the force in the bolt or tie down rod at the beginning and end of the cycles when the

specimen had no lateral force.

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Specimen W1

Referring to Figure A.2, the tie downs and anchor bolts experienced a loss of pretension

during the experiment, as the forces of anchor bolt #1 show, which can be contributed to

loosening of the bolts, localized settling, localized damage, or movement of the sill plate. But

most specimens have one anchor bolt which experienced a gain in pretension of the bolt over the

experiment, similar to anchor bolt #2, which may be contributed to a slight elongation of the bolt

due to rotation as the specimen shifted during the experiment and lodged on the edge of the holes

in the test rig. As expected, the maximum axial forces occurred at the tie downs and the minimum

forces occurred in the interior-most bolts. For example, during the 0.5% interstory drift cycles, at

the maximum lateral force capacity of the specimen, the tie-down forces correspond to 72-78% of

the theoretical uplift force – equal to the lateral load for a square specimen – at the tie downs,

18% at the exterior-most anchor bolt, and 1-2% at the interior anchor bolts, accounting for the

entire uplift force in the sill. Referring to Figure A.2, the specimen maintained the distribution of

axial forces to the anchor bolts and tie downs during the larger displacements. The largest forces

occurred in the tie-downs and exterior anchor bolts while the lowest forces occurred in the

interior anchor bolts. However, due to the separation between frame and wallboard, the forces

became concentrated in the end studs rather than being distributed across the wall. Therefore,

with the exception of the edge bolts, the forces in the tie downs increased while forces in the

anchor bolts decreased.

Specimen W2

The forces of the East tie down were not used for analysis of this specimen due to off-

scale readings of the instrument, which were addressed following the test. The maximum force

occurred in the tie down, with an axial force of 74% of the theoretical uplift force applied to the

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specimen. When compared to the distribution of forces in W1, the adhesive caused the anchor

bolts to have a slightly different distribution through the 0.4% interstory drift where anchor bolt

#3 has a larger force than the neighboring bolts. Following the propagation of the crack, the

forces redistributed similar to W1, and all of the anchor bolts experienced reduced forces while

the force in the tie down increased. Similar to the behavior of the anchor bolts in W1, the forces

in the anchor bolts reduced during the post 0.5% interstory drift cycles while the force in the tie

down increased.

Specimen W3

Figure A.2 shows that the distribution of axial forces follows the same pattern as the

previous specimens, although the anchor bolts have a higher percentage of the uplift force due to

the flexibility at the sill plate from the HDPE pads placed beneath the plate washers. The tie

downs receive the largest forces while anchor bolts #2 and #4 receive the smallest. Through the

applied displacements of these cycles, the forces generally increased through the 0.4% cycles,

after which the forces in anchor bolt #1 and the West tie down increase while the forces in anchor

bolts #2 through #5 and the East tie down decrease. The local decrease in forces in the East tie

down and anchor bolt #1 during the 0.3% interstory drift correspond to the crack that formed at

the bottom of the East side of the wall, depicted in Figure 4.19a. Similarly, the decrease in forces

in the interior anchor bolts, #2 through #5, during the 0.5% interstory drift corresponds to the

increasing crack width at the joint between wallboard panels. The distribution of axial forces to

the anchor bolts and tie downs at larger deformations follows the distribution described in the

smaller displacements where the tie downs record the largest forces while anchor bolts #2 and #4

record the smallest.

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Specimen W4

The largest forces occur in the tie downs while each of the anchor bolts receives

approximately 7% or less of the theoretical uplift. The chart shows that the axial forces in the

anchor bolts decrease at the exterior-most bolt during the 0.2% cycles and progressed inwards

during the larger drifts. These decreases correspond to the observed separation between

wallboard and frame. The decrease in axial forces in the anchor bolts observed during the smaller

displacement cycles continued at large deformations such that the forces in anchor bolts during

the larger cycles is negligible. Through these larger displacements, the force in the tie down at

the east side of the wall increased while the force in the tie down at the west side of the wall

decreased.

Specimen W5

Similar to the previous tests, the largest forces were observed in the tie downs. However,

a new force distribution was observed where the largest axial anchor bolt force occurred in one of

the interior-most anchor bolts, #3. During the 0.4% interstory drift, when the wall achieved its

maximum strength, the tie downs presented axial forces equivalent to 44-54% of the lateral force

in the wall, while anchor bolt #3 presented 10%, and the other bolts presented 2-4% of the lateral

force. Following the peak strength, the forces in the anchor bolts generally decreased while the

forces in the tie downs generally increased. In addition to the reduction of forces distributed to the

anchor bolts at larger interstory drifts, the forces in the tie downs begin to decrease, which may be

attributed to the limitations of uplift of the end studs provided by the combination of tie down and

strap.

227

Specimen W6

Corresponding to the peak strength of the wall, the anchor bolts experienced peak axial

forces ranging between 3% in the interior anchor bolt #4 and 11% in the exterior most anchor bolt

#1. Similar to W5, the interior anchor bolt #3 experienced larger forces than the neighboring

bolts during these smaller displacements. The tie forces continue to increase during the larger

displacements while the interior anchor bolts decrease to axial forces equivalent to 3% or less of

the lateral force within the wall. In these larger displacements, the exterior most anchor bolt, #1,

increased to the equivalent of 28% of the lateral force within the wall. This unique increase is

most likely caused by the bent strap that was installed at exterior corners of the wall which

extends past the location of the anchor bolt.

Specimen W7

As shown in Figure A.1, the instrumented tie downs were moved to the ends of the return

walls to determine how forces are much the return walls contribute to resisting the uplift of

specimens with returns. The anchor bolts in the return walls were not instrumented, but

presumably the bolts took a share of the uplift forces similar to the forces in the tie downs.

Referring to the Figure A.2, during the 0.4% cycles in which the wall experienced its maximum

strength, the tie downs recorded maximum axial forces equivalent to 9% to 12% of the lateral

force within the wall. In contrast to the previous tests, where the axial forces in the anchor bolts

increased through the displacement cycles in which the wall experienced its maximum strength,

the forces of the anchor bolts of this specimen only increased through the 0.075% or 0.1%

interstory drift and generally decreased afterwards. As depicted in Figure A.2, the axial forces in

the tie downs at the ends of the returns continued to increase to 29-33% of the lateral force of the

228

wall through the larger displacements. The axial forces in the anchor bolts continued to decrease

through the larger cycles to forces of less than 2% of the lateral force within the wall.

Specimen W8

During the 0.4% interstory drift cycles, when the wall experienced its maximum strength,

the tie downs recorded forces equivalent to 8% and 21% of the lateral force within the wall. At

the same time, the anchor bolts recorded forces equivalent to 0.1-0.5% of the lateral force. This

distribution of forces to the anchor bolts, while being low, returns to the expected distribution

where the outer-most bolts maintain the larger forces and the interior bolts maintain the smallest.

The difference in the recorded tie down forces shows that the enhanced corner stud assembly,

while improving the behavior of the main wall, does not evenly transfer the forces to the ends of

the return. During the cycles of deformation larger than 0.5% Interstory drift, the forces in the

anchor bolts decreased to negligible during these displacements. Additionally, the figure shows

that the forces in the tie downs increased and the imbalance of forces transferred around the

corners to the end walls became more apparent.

Specimen W9

As shown in Figure A.1, the locations of instrumented tie downs were adjusted to observe

the uplift forces at the ends of the large wall pier and the north end of the east return. Through

these, it can be determined that during the 0.4% interstory drift, when the wall reached its

maximum strength, the ends of the large pier experience axial forces of approximately 70% of the

lateral force within the specimen. The anchor bolts located closer to the door opening recorded

larger axial forces than those located closer to the return walls. Figure A.2 shows that the

distribution of axial forces to the anchor bolts observed within the smaller displacement cycles

229

continued through the larger displacements. Following the behavior of previous tests, the forces

in the interior anchor bolts decreased after separation of the wallboard occurred while the forces

in the tie downs increased.

Specimen W10

Similar to previous tests, the forces in the tie downs generally increase throughout the test

and the transfer of forces to the tie downs at the ends of the wall is unequal. During the 0.3%

interstory drift, when the wall reached its maximum capacity, the axial forces in the anchor bolts

were 0.1% to 0.4% of the lateral force in the wall, and the forces in the tie downs were 2-4% and

10% of the lateral force at the ends of the returns and main wall, respectively. The axial forces of

the anchor bolts and tie downs follow the same observed the same observed distributions during

the larger displacements.

Specimen W11

This specimen, generally, follows a combination of the uplift behavior described in

Specimens W9 and W10. During the 0.3% interstory drift, when the specimen experienced the

maximum strength, the tie downs recorded forces equivalent to 23%, 13%, and 6% of the lateral

force within the wall at the West end of the large wall pier, East end of the large pier, and North

end of the East return, respectively. The anchor bolts recorded forces between 2% and 9% of the

lateral force.

Specimen S1

Figure A.2 shows that the largest forces were recorded at the tie downs while the anchor

bolts each recorded maximum forces equivalent to 4% or less of the theoretical uplift force –

230

equal to the lateral load for a square specimen. The chart also shows that the maximum recorded

force in each of the anchor bolts and tie downs generally increased through the 0.5% interstory

drift. Figure A.2 shows that the maximum recorded forces in the anchor bolt and tie downs during

the larger displacements maintain a similar distribution as during the smaller displacements.

During the 0.75% interstory drift, when the specimen achieved its maximum strength capacity,

the tie downs recorded forces equivalent to 34-37% of the lateral force within the specimen and

the anchor bolts recorded forces equivalent to 0-4% of the lateral force. Following the peak, the

forces in the East tie down and anchor bolts generally decreased and the force in the West tie

down increased. The difference in tie down forces is most likely caused by the asymmetry that

causes the difference in specimen strength between the “positive” and “negative” displacements.

Specimen S2

Figure A.2 shows the maximum recorded values for the anchor bolts and tie downs

during the 0-0.5% interstory drift cycles as an equivalent to the percentage of lateral force within

the specimen. As expected, largest forces occurred at the exterior of the specimen and reduced as

it approached the inner-most anchor bolts. During the 0.4% interstory drift cycles, when the

specimen attained its maximum strength capacity, the tie downs recorded forces equivalent to

56%-82% of the lateral force, the exterior most anchor bolt recorded 7% equivalent force and the

interior anchor bolts recorded 1-3% equivalent force. The difference in recorded forces for the

East and West tie-downs that was noted in the control specimen increased within this specimen

and ranges between 10% and 25% during the 0-0.5% interstory drift cycles. The distribution of

axial forces to the tie downs and anchor bolts remained the same through the larger

displacements. The difference between the forces in the East and West tie downs increased to a

73% by the end of the test.

231

Specimen S3

Figure A.2 illustrates that the axial forces increase in all of the bolts and tie downs

through the 0.1% drift to match the local peak strength of the specimen. After the local peak, the

forces in the tie downs at the ends of the main wall began to decrease while the forces in the

anchor bolts in the main wall and tie down in the return wall continue to increase. The forces in

the anchor bolts increased during the larger displacements showing the difference in forces at the

East and West ends of the wall that was noticed in the previous specimens.

Specimen S4

The anchor bolts and tie downs at the ends of the wall experienced local peak forces

during the 0.2-0.4% cycles corresponding to the peak strength of the wall that occurred in the

0.3% interstory drift. The chart shows that the largest forces of this specimen occur in the tie-

downs at the East end of the wall, while the anchor bolts and West tie-down record axial forces of

less than 5% of the theoretical uplift. Similar to the previous specimens, the forces in the tie

downs continue to increase during the larger displacements. However, unlike the previous

specimen, the force in the tie down at the end of the wall is greater than the tie down in the end

return.

Specimen W-DG

Following the behavior of the force-deformation plot, the forces in the anchor bolts and

tie downs increase through the 0.2%-0.3% interstory drift cycles, corresponding to when inelastic

damage began to occur. In the subsequent cycles, as visible damage occurs to the specimen, the

axial forces in the anchor bolts become negligible and the forces in the tie down plateau and/or

232

reduce. The distribution of forces remains similar during the larger displacements as the forces in

the tie downs increase and the forces in the anchor bolts remain negligible.

Specimen W-PLY

The distribution of forces to the anchor bolts and tie-downs illustrate that the largest

forces occurred at the ends of the main wall in the tie downs and generally decreased towards the

inner-most anchor bolts. However, the low values of the recorded forces in the tie down at the

end of the return wall suggest that the forces did not transfer around the corner of the wall as well

as other specimens. Additionally, the figure shows that forces in the anchor bolts increased

through the 0.5% cycles even though damages occurred at the bottom of the interior wallboard

during the 0.3% interstory drift. At larger deformations, the figure suggests that the forces in the

anchor bolts and tie downs increased through the 1.0% interstory drift cycles when the specimen

attained its maximum strength capacity. In the subsequent cycles, the forces in the tie downs

increased through the 1.25% cycles where the maximum recorded forces equivalent to 42.6%,

and 62.8% at the West and East ends of the main wall, respectively, occurred. Similar to the

previous cycles, the tie down at the end of the return wall recorded low forces suggesting that the

uplift forces did not transfer around the corner.

Specimen W-STU

The anchor bolts and tie-downs are distributed such that the forces are the largest at the

ends of the main wall and decrease as progress towards inner-most anchor bolts. Referring to

Figure A.2, local peaks in the recorded forces occur in the anchor bolts within the 0.2% to 0.4%

cycles, which corresponds to the adhesive failures and visible damages that occurred on the

interior face of the wall during those cycles. Furthermore, the distribution of axial forces to the

233

anchor bolts and tie-downs remained the same during the larger displacements. The largest

forces occurred in the tie-downs at the end of the main wall and decreased as progress towards

the inner-most anchor bolts.

234

Figure A.1: Tie-down (TD) and anchor bolt locations (numeric) for various wall configurations.

Layout 1: 8 ft. wall without returns

Layout 2: 8 ft. wall with T‐returns

Layout 3: 8 ft. wall with T‐returns and door opening

Layout 4: 8 ft. (exterior) wall with L‐returns

Layout 5: 16 ft. wall with T‐returns

235

Layout 6: 8 ft. wall with T‐returns and door opening

236

Figure A.2 Measured axial forces in tie-downs and anchor bolts P

ost

0.5%

In

ters

tory

Dri

ft R

ange

0-

0.5%

In

ters

tory

Dri

ft R

ange

T

est

Sp

ecim

en

W1

Lay

out 1

W2

Lay

out 1

237

Pos

t 0.

5% I

nte

rsto

ry D

rift

Ran

ge

0-0.

5% I

nte

rsto

ry D

rift

Ran

ge

Tes

t S

pec

imen

W3

Lay

out 1

W4

Lay

out 1

238

Pos

t 0.

5% I

nte

rsto

ry D

rift

Ran

ge

0-0.

5% I

nte

rsto

ry D

rift

Ran

ge

Tes

t S

pec

imen

W5

Lay

out 1

W6

Lay

out 1

239

Pos

t 0.

5% I

nte

rsto

ry D

rift

Ran

ge

0-0.

5% I

nte

rsto

ry D

rift

Ran

ge

Tes

t S

pec

imen

W7

Lay

out 2

W8

Lay

out 2

240

Pos

t 0.

5% I

nte

rsto

ry D

rift

Ran

ge

0-0.

5% I

nte

rsto

ry D

rift

Ran

ge

Tes

t S

pec

imen

W9

Lay

out 3

W10

L

ayou

t 5

241

Pos

t 0.

5% I

nte

rsto

ry D

rift

Ran

ge

0-0.

5% I

nte

rsto

ry D

rift

Ran

ge

Tes

t S

pec

imen

W11

L

ayou

t 6

S1

Lay

out 1

242

Pos

t 0.

5% I

nte

rsto

ry D

rift

Ran

ge

0-0.

5% I

nte

rsto

ry D

rift

Ran

ge

Tes

t S

pec

imen

S2

Lay

out 1

S3

Lay

out 2

243

Pos

t 0.

5% I

nte

rsto

ry D

rift

Ran

ge

0-0.

5% I

nte

rsto

ry D

rift

Ran

ge

Tes

t S

pec

imen

S4

Lay

out 2

W-D

G

Lay

out 4

244

Pos

t 0.

5% I

nte

rsto

ry D

rift

Ran

ge

0-0.

5% I

nte

rsto

ry D

rift

Ran

ge

Tes

t S

pec

imen

W-P

LY

L

ayou

t 4

W-S

TU

L

ayou

t 4

large-scale tests of seismically enhanced planar walls for …zq223jt4225/tr186_hopkins.pdf ·...

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