des431 - demystifying diaphragm design · education systems (aia/ces), provider # 50111237....

Copyright © 2019 American Wood Council.All rights reserved.

Demystifying Diaphragm DesignDES431

John “Buddy” Showalter, PEVice President Technology TransferAmerican Wood Council

Michelle Kam-Biron, PE, SE, SECBSenior Director, EducationAmerican Wood Council

D e m y s t i f y i n g D i a p h r a g m D e s i g n2

This presentation is protected by US and International Copyright laws. Reproduction,

distribution, display and use of the presentation without written permission of AWC is prohibited.

© American Wood Council 2019

COPYRIGHT



Participants may download the presentation here: http://www.awc.org/education/resources

The American Wood Council is a Registered Provider with The American Institute of Architects Continuing Education Systems (AIA/CES), Provider # 50111237.

Credit(s) earned on completion of this course will be reported to AIA CES for AIA members. Certificates of Completion for both AIA members and non-AIA members are available upon request.

This course is registered with AIA CES for continuing professional education. As such, it does not include content that may be deemed or construed to be an approval or endorsement by the AIA of any material of construction or any method or manner of handling, using, distributing, or dealing in any material or product.

Questions related to specific materials, methods, and services will be addressed at the conclusion of this presentation.


COURSE DESCRIPTIONThe 2018 International Building Code (IBC) specifies that structures using wood-framed shear walls and diaphragms to resist wind, seismic and other lateral loads shall be designed and constructed in accordance with AWC’s 2015 Special Design Provisions for Wind and Seismic (SDPWS) or 2018 Wood Frame Construction Manual (WFCM) for One- and Two-Family Dwellings. Both code-referenced standards provide procedures for designing diaphragms for wood construction. This presentation will demystify diaphragm design by providing wind and seismic design examples for in-plane lateral design of wood- and gypsum-sheathed diaphragms including a brief overview of high-load diaphragms.



LEARNING OBJECTIVES

Calculate wood-frame diaphragm deflection using the 2015 SDPWS

Wood-Frame Diaphragm Deflection

Compare the difference between the 3-term and 4-term deflection equation in the 2015 SDPWS

3-Term & 4-Term Deflections

Analyze wood- and gypsum-sheathed diaphragms using prescriptive and engineered procedures

Wood- & Gypsum-Sheathed Diaphragms

Evaluate special inspection requirements as required for high-load diaphragms

High-Load Diaphragms

Upon completion, participants will be better able to:

1

2 4

3


POLLING QUESTION

1. What is your profession?a) Architectb) Engineerc) Code Officiald) Fire Servicee) Builder/Manufacturer/Other



2. If I were to categorize my experience with design or plan review of structural wood construction, I would be:

a) Groot (I have limited exposure)

b) Rocket Raccoon

c) Black Widow

d) Captain America

e) Iron Man (I could teach this course)

POLLING QUESTION


OUTLINE

• Basic Lateral Load Overview and Code acceptance of 2015 SDPWS

• Prescriptive Diaphragm Example• Diaphragm Deflection Equation• Diaphragm Deflection Example• High Load Diaphragms• FAQ• Resources



GENERAL LATERAL LOAD PATH

D e m y s t i f y i n g D i a p h r a g m D e s i g n1 0

Load Path

Ties

ChordT T

ChordC C

w

Diaphragm reaction goes to shear walls

Diaphragms supporting Masonry or Concrete Structural Walls -Seismic Design Category C, D, E, & FDiaphragms shall be provided with continuous ties or struts between diaphragm chords to distribute these anchorage forces into the diaphragms (ASCE 7 - 16 sec. 12.11.2.2.1)

FROM DIAPHRAGM LOAD PATH



Load Pathw

W

v

L

v

FROM DIAPHRAGM TO SHEAR WALLS


SDPWS (ANSI/AWC SDPWS-15)Special Design Provisions for Wind and Seismic

2015 IBC & 2018 IBC• Mandatory• References 2015 SDPWS in

Section 2305 for lateral design and construction



SDPWS (ANSI/AWC SDPWS-15)Special Design Provisions for Wind and Seismic

2015 IBC & 2018 IBC• Mandatory• References 2015 SDPWS in

Section 2305 for lateral design and construction

ASCE 7-10


OUTLINE

Photo courtesy: KC Kim GB Construction


• Prescriptive Diaphragm Example

• Diaphragm Deflection Equation• Diaphragm Deflection Example• High Load Diaphragms• FAQ• Resources

WFCMWOOD FRAME CONSTRUCTION MANUALfor One- and Two-Family Dwellings

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W O R K B O O KDESIGN OF WOOD FRAME BUILDINGS FOR HIGH WIND, SNOW, AND SEISMIC LOADS

Demystifying Diaphragm Design 15

BUILDING DESCRIPTION

Figure 1: Isometric view (roof overhangs not shown).


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BUILDING DESCRIPTION

North

Wall Heights = 9' Windows Finished Grade to Foundation Top = 1' Typical 3'x4'-6" Floor Assembly Height = 1' Foyer 6'x4'-6" Roof Pitch = 7:12 Kitchen 4'x4'-6" House Mean Roof Height = 24.7' Bath 4'x6' Roof Overhangs = 2' Doors Building Length (L) = 40' Typical 3'x7'-6" Building Width (W) = 32' Foyer 6'x7'-6" Top plate to ridge height = 9.3' Kitchen 9'x7'-6"


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LOADS ON THE BUILDING

Structural systems in the WFCM 2018 Edition have been sized using dead, live, snow, seismic and wind loads in accordance with ASCE/SEI 7-16 Minimum Design Loads and Associated Criteria for Buildings and Other Structures. Provisions of the 2018 International Residential Code (IRC) are referenced as needed.

Lateral Loads:

Wind:

3-second gust wind speed in Exposure Category B (700 yr. return) = 160 mph

Seismic:

Simplified Procedure (ASCE 7-16 Section 12.14)

Seismic Design Category (SDC) – (ASCE 7-16 Section 11.6 and IRC Subcategory) = D1

Vertical force distribution factor (F) – (ASCE 7-16 Section 12.14.8.1) = 1.2

Gravity Loads*:

Roof: Roof Dead Load = 10 psf Ground Snow Load, Pg = 30 psf Roof Live Load = 20 psf Ceiling: Roof Ceiling Load = 10 psf *Assumptions vary for wind and seismic dead loads Deflection limits per 2018 IRC Roof Rafters with flexible Ceiling Attached L/Δ = 240 Roof Rafters with no Ceiling Attached L/Δ = 180 Raised Ceiling Joists with flexible finish L/Δ = 240 Floor Joists L/Δ = 360 Exterior Studs (gypsum interior) H/Δ = 180

Note: See comparable deflection limits in 2018 IBC section 2308 for joists and rafters.

Floors: First Floor Live Load = 40 psf Second Floor Live Load = 30 psf Attic Floor Live Load = 30 psf Floor Dead Load = 10 psf

Walls: Wall Dead Load = 11 psf

d. Deflection for exterior walls with interior gypsum board finish shall be limited to an allowable deflection of H/180.

2018 International Residential Code for One- and Two-Family

Dwellings, International Code Council, Inc., Washington, DC. Reproduced with permission. All rights reserved. www.iccsafe.org


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WFCM APPLICABILITY LIMITATIONS

The following table is used to determine whether the building geometry is within the applicability limitations of the WFCM. Conditions not complying with the limitations shall be designed in accordance with accepted engineer practice (see WFCM 1.1.3).

Table W1.1 Applicability Limitations

Attribute Limitation Design Case

BUILDING DIMENSIONS

Mean Roof Height (MRH) maximum 33' 24.7'

Number of Stories maximum 3 3

Building Dimension (L or W) maximum 80' 40'


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PRESCRIPTIVE DESIGN LIMITATIONS

The following table is used to determine whether the building geometry is within the applicability limitations of the WFCM Chapter 3 prescriptive provisions. Conditions not complying with the limitations shall be designed in accordance with WFCM Chapter 2 (see WFCM 3.1.3).

Table W1.2 Prescriptive Design Limitations

Element Attribute Limitation Design

Case

FLOOR SYSTEMS (3.1.3.2)

Lumber

Joists

Joist Span 26' 16'

Joist Spacing 24" 16"

Cantilevers/Setback - Supporting loadbearing walls d N/A

Cantilevers - Supporting non-loadbearing walls L/4 N/A

Floor

Diaphragms

Vertical Floor Offset df N/A

Floor Diaphragm Aspect Ratio Table 3.16B Lmin=12.5' and Lmax=74' (interpolated); Table 3.16C1 Lmax=80'

L=40' L=25.5' (attic)

Floor Diaphragm Openings Lesser of 12' or 50% of Diaphragm Dimension

12'

WALL SYSTEMS (3.1.3.3)

Wall Studs

Loadbearing Wall Height 10' 9'

Non-Loadbearing Wall Height 20' 18.3'

Wall Stud Spacing 24" 16"

Shear Walls

Shear Wall Line Offset 4' 0

Shear Wall Story Offset No offset unless per Exception 0

Shear Wall Segment Aspect Ratio 3½:1 (WSP) 2:1 (Gypsum) 3:1

ROOF SYSTEMS (3.1.3.4)

Lumber

Rafters

Rafter Span (Horizontal Projection) 26' 16'

Rafter Spacing 24" 16"

Eave Overhang Length Lesser of 2' or rafter length/3 2'

Rake Overhang Length* Lesser of 2' or outlooker length/2 2'

Roof Slope 1.5 - 12:12 7:12

Roof

Diaphragms Roof Diaphragm Aspect Ratio

Table 3.16A1 Lmin=12.7' and Lmax=70.6' (interpolated); Table 3.16C1 Lmax=80'

L=40

*Rake overhangs using lookout blocks shall not exceed 9". (WFCM 3.1.3.4c)


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WFCMWOOD FRAME CONSTRUCTION MANUALfor One- and Two-Family Dwellings

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WFCM2 0 1 8E D I T I O N


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Table 3.16A1 Roof Diaphragm Limits for Wind 1

(Applicable to All Roof Slopes with and without Roof Irregularities)

Exposure BAll Slopes

Min Max Min Max Min Max Min Max Min Max Min Max Min Max Min Max Min Max Min Max Min Max Min Max Min Max Min Max

12 4 36 4 36 4 36 4 36 4 36 4 36 4 36 4 36 4 36 4 36 4 35 4 31 5 28 6 2416 6 48 6 48 6 48 6 48 6 48 6 48 6 48 6 48 6 48 6 48 6 47 6 42 6 37 7 3220 7 60 7 60 7 60 7 60 7 60 7 60 7 60 7 60 7 60 7 60 7 59 7 52 8 47 9 4024 8 72 8 72 8 72 8 72 8 72 8 72 8 72 8 72 8 72 8 72 8 71 8 63 9 56 11 4828 10 80 10 80 10 80 10 80 10 80 10 80 10 80 10 80 10 80 10 80 10 80 10 74 11 66 13 5632 11 80 11 80 11 80 11 80 11 80 11 80 11 80 11 80 11 80 11 80 11 80 11 80 12 75 14 6436 12 80 12 80 12 80 12 80 12 80 12 80 12 80 12 80 12 80 12 80 12 80 12 80 14 80 16 7212 4 36 4 36 4 36 4 36 4 36 4 36 4 36 4 36 4 33 5 28 5 25 6 22 6 20 7 1716 6 48 6 48 6 48 6 48 6 48 6 48 6 48 6 48 6 44 6 38 7 33 8 30 8 26 10 2220 7 60 7 60 7 60 7 60 7 60 7 60 7 60 7 60 7 55 7 48 8 42 9 37 10 33 12 2824 8 72 8 72 8 72 8 72 8 72 8 72 8 72 8 72 8 66 9 57 10 50 11 45 12 40 14 3428 10 80 10 80 10 80 10 80 10 80 10 80 10 80 10 80 10 77 10 67 11 59 13 52 14 46 17 3932 11 80 11 80 11 80 11 80 11 80 11 80 11 80 11 80 11 80 12 77 13 67 15 60 16 53 19 4536 12 80 12 80 12 80 12 80 12 80 12 80 12 80 12 80 12 80 13 80 15 76 16 67 18 60 21 5112 4 36 4 36 4 36 4 36 4 36 4 36 4 35 4 29 5 25 6 22 6 19 7 17 8 15 9 1316 6 48 6 48 6 48 6 48 6 48 6 48 6 46 6 39 7 34 7 29 8 26 9 23 10 20 12 1720 7 60 7 60 7 60 7 60 7 60 7 60 7 58 7 49 8 42 9 37 10 32 12 29 13 26 15 2224 8 72 8 72 8 72 8 72 8 72 8 72 8 70 8 59 10 51 11 44 12 39 14 34 15 31 18 2628 10 80 10 80 10 80 10 80 10 80 10 80 10 80 10 69 11 60 13 52 14 46 16 40 18 36 21 3132 11 80 11 80 11 80 11 80 11 80 11 80 11 80 11 79 13 68 14 59 16 52 18 46 20 41 24 3536 12 80 12 80 12 80 12 80 12 80 12 80 12 80 12 80 14 77 16 67 18 59 20 52 23 46 27 3912 4 36 4 36 4 36 4 36 4 34 4 31 4 28 5 24 6 21 7 18 8 16 8 14 9 1216 6 48 6 48 6 48 6 48 6 45 6 41 6 38 7 32 8 28 9 24 10 21 11 19 12 1620 7 60 7 60 7 60 7 60 7 56 7 52 7 47 8 40 10 35 11 30 12 26 14 23 15 2124 8 72 8 72 8 72 8 72 8 68 8 62 8 57 10 48 11 42 13 36 15 32 16 28 18 2528 10 80 10 80 10 80 10 80 10 79 10 72 10 66 11 57 13 49 15 42 17 37 19 33 21 2932 11 80 11 80 11 80 11 80 11 80 11 80 11 76 13 65 15 56 17 48 19 43 22 38 24 3336 12 80 12 80 12 80 12 80 12 80 12 80 12 80 14 73 17 63 19 55 22 48 24 42 27 38

1

2

3

195110

5

95 100

Roof sheathing applied with long dimension perpendicular to roof framing and staggered.

150115 180

15

120 160

20

105 130

Roof diaphragm length dimension measured perpendicular to direction of framing span.

170Wind Speed

3-second gust (mph) (See Figure 1.1)

Maximum Top Plate to Ridge

Height (ft)

Roof Diaphragm Width (ft) 2

Roof Diaphragm Length (ft) 3

Roof diaphragm width dimension measured parallel to direction of framing span.

14090

10


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Table 3.16B Floor Diaphragm Limits for Wind 1

Min Max Min Max Min Max Min Max Min Max Min Max Min Max Min Max Min Max Min Max Min Max Min Max Min Max Min Max

12 4 36 4 36 4 36 4 36 4 36 4 36 4 36 4 36 4 36 4 35 5 31 5 27 6 24 7 2116 6 48 6 48 6 48 6 48 6 48 6 48 6 48 6 48 6 48 6 47 6 42 7 37 7 33 9 2820 7 60 7 60 7 60 7 60 7 60 7 60 7 60 7 60 7 60 7 59 7 52 8 46 9 41 11 3524 8 72 8 72 8 72 8 72 8 72 8 72 8 72 8 72 8 72 8 71 9 63 10 55 11 49 13 4228 10 80 10 80 10 80 10 80 10 80 10 80 10 80 10 80 10 80 10 80 10 73 11 65 13 58 15 4932 11 80 11 80 11 80 11 80 11 80 11 80 11 80 11 80 11 80 11 80 11 80 13 74 14 66 17 5636 12 80 12 80 12 80 12 80 12 80 12 80 12 80 12 80 12 80 12 80 13 80 14 80 16 74 19 6312 4 36 4 36 4 36 4 36 4 36 4 36 4 36 4 36 4 33 5 29 6 25 6 22 7 20 8 1716 6 48 6 48 6 48 6 48 6 48 6 48 6 48 6 48 6 45 6 39 7 34 8 30 9 27 11 2320 7 60 7 60 7 60 7 60 7 60 7 60 7 60 7 60 7 56 8 49 9 43 10 38 11 34 13 2924 8 72 8 72 8 72 8 72 8 72 8 72 8 72 8 72 8 67 9 58 11 51 12 45 13 40 15 3428 10 80 10 80 10 80 10 80 10 80 10 80 10 80 10 80 10 78 11 68 12 60 14 53 15 47 18 4032 11 80 11 80 11 80 11 80 11 80 11 80 11 80 11 80 11 80 12 78 14 68 16 61 17 54 20 4636 12 80 12 80 12 80 12 80 12 80 12 80 12 80 12 80 12 80 14 80 16 77 18 68 20 61 23 52

1

2

3

8

180 195160 170

Floor Diaphragm Length (ft) 3

Floor diaphragm width dimension measured parallel to direction of framing span.

Wind Speed 3-second gust (mph)

(See Figure 1.1)

Floor sheathing applied with long dimension perpendicular to floor framing and staggered.

95 100 105

10

Wall Height (ft)

Floor Diaphragm Width (ft) 2

90

Floor diaphragm length dimension measured perpendicular to direction of framing span.

115 120 130 140 150110

Exposure B


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Table 3.16C1 Diaphragm Limits for Seismic (Dead Load Assumptions: Roof/ceiling = 15 psf, Floor = 12 psf, Partition = 8 psf, Wall = 110 plf;

Ground Snow Load = 30 psf; Lateral force resisting system: Wood structural panel shear walls)

GSL = 30

ft ft ft12 0.07 36 0.14 36 0.22 3616 0.08 48 0.16 48 0.25 4820 0.10 60 0.19 60 0.28 6024 0.11 72 0.21 72 0.32 7228 0.11 80 0.22 80 0.34 8032 0.11 80 0.21 80 0.32 8036 0.11 80 0.21 80 0.31 8012 0.07 36 0.14 36 0.22 3616 0.09 48 0.17 48 0.25 4820 0.10 60 0.19 60 0.29 6024 0.11 72 0.21 72 0.32 7228 0.12 80 0.23 80 0.34 8032 0.11 80 0.22 80 0.33 8036 0.11 80 0.21 80 0.32 80

ft ft ft

12 0.29 36 0.36 36 0.51 36

16 0.33 48 0.41 48 0.58 48

20 0.38 60 0.47 60 0.66 60

24 0.43 72 0.53 72 0.74 72

28 0.45 80 0.56 80 0.78 80

32 0.43 80 0.54 80 0.76 80

36 0.42 80 0.52 80 0.73 80

12 0.29 36 0.36 36 0.51 36

16 0.34 48 0.42 48 0.59 48

20 0.39 60 0.48 60 0.67 60

24 0.43 72 0.54 72 0.76 72

28 0.46 80 0.57 80 0.80 80

32 0.44 80 0.55 80 0.77 80

36 0.43 80 0.53 80 0.75 80

See footnotes 1‐4.

Floor

Diaphragm

Load Ratio3

Maximum Diaphragm Dimension,

L1,2,4

Diaphragm

Load Ratio3


L1,2,4

Minimum Diaphragm

Dimension, W (ft)

SDC D0

Diaphragm

Load Ratio3

Roof/Ceiling

Diaphragm

SDC D1 SDC D2


L1,2,4

Floor


L1,2,4

SDC B

Diaphragm Diaphragm

Load Ratio3


L1,2,4

Diaphragm

Load Ratio3Diaphragm

Load Ratio3

Roof/Ceiling

Minimum Diaphragm

Dimension, W (ft)

SDC A


L1,2,4

SDC C


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PRESCRIPTIVE DESIGN


Table 3.16A1 Roof Diaphragm Limits for Wind (Applicable to All Roof Slopes with and without Roof Irregularities)

Description: Minimum and maximum roof diaphragm lengths for given roof diaphragm widths and wind speeds based on roof diaphragm limitations.

Procedure: Using the procedures from Chapter 2 for calculating wind loads, determine the minimum and maximum roof diaphragm lengths permitted based on roof dia-phragm capacity. To account for possible irregularities in roof shape caused by roof features such as dormers or complex roof framing layouts, wind loads are cal-culated assuming conservative pressure coefficients regardless of the actual roof pitch associated with the top plate-to-ridge height and roof diaphragm width dimen-sions.

Background: Capacities for horizontal diaphragm as-semblies (roof and floor) are based on sheathing thickness, nail size, panel edge nailing, and supported panel edges.

Example: Given – 150 mph, Exposure B, 1 story slab-on-grade, 10' maximum top plate to ridge height, 24' roof diaphragm width.

RoofDiaphragmLength

RoofDiaphragm

Direc�on ofRoof Framing

Roof Sheathing Applied withLong DimensionPerpendicular to Roof Framing10 � Top Plate

to Ridge Height

24 �Roof Diaphragm

Width

The minimum diaphragm aspect ratio limit is equal to 0.33 (1:3) and the maximum diaphragm aspect ratio limit is equal to 3.0 (3:1).

Calculation of Minimum Roof Diaphragm Length

Calculate minimum roof diaphragm length, LMin, based on the maximum value obtained from the following two calculations: a) Calculate the roof diaphragm length required based on wind load acting parallel to the ridge (Note: pressure coefficients for wind acting parallel to ridge are constant and do not vary with roof pitch):

Roof diaphragm load for a top plate to ridge height of 10 feet (i.e. 10:12 roof pitch for a roof diaphragm width of 24 feet): WRD = 155 plf (Table 2.5B)

Calculate load into shear wall:

From roof diaphragm: V = [155 plf (24 ft)] / 2

= 1,860 lbs

Using 2015 SDPWS Table 4.2C Nominal Unit Shear Ca-pacities for Wood-Frame Diaphragms and applying the (1/2.0) ASD reduction factor per SDPWS Section 4.2.3:

vRD = 450 plf / (2.0) (3/8 nominal panel thickness, 2" nominal width framing, and Case 3)

vRD = 225 plf

Minimum roof diaphragm length: LMin = 1,860 lbs / 225 plf

= 9 ft (rounded up from 8.3 ft)

b) Calculate the minimum roof diaphragm length needed based on aspect ratio limits:

LMin = 24 ft / 3

= 8 ft

The minimum roof diaphragm length is:

LMin = 9 ft (WFCM Table 3.16A1)


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COMMENTARY TO THE WOOD FRAME CONSTRUCTION MANUAL


Calculation of Maximum Roof Diaphragm Length

Calculate the maximum roof diaphragm length , LMax, based on the minimum value obtained from the following three calculations: a) Calculate roof diaphragm length needed based on the wind load acting perpendicular to the ridge:

Roof diaphragm load for a top plate to ridge height of 10 feet utilizing conservative pressure coefficients associated with a 12:12 roof pitch are calculated as follows:

The lateral load on the roof diaphragm will take load from half the wall below and load directly applied to the diaphragm.

Calculate wind forces in the roof diaphragm:

p = q(GCpf - GCpi)where:

p = pressure on the roof/walls

q = 21.15 psf (See Table C1.1)

Calculated the average pressure on the wall for a 12:12 roof pitch:

Interior Zone End ZoneWindward Leeward Windward Leeward

GCpf 0.56 -0.37 0.69 -0.48GCpi 0.18 0.18 0.18 0.18p (psf) 8.0 -11.6 10.8 -14.0

pwall = [19.6(L-X) + 24.8(X)] / L

= [19.6 psf (18 ft) + 24.8 psf (6 ft)] / 24

= 20.9 psfwhere: L = Building Length (parallel to ridge)

X = End Zone Length

Calculate the average pressure on the roof for a 12:12 roof pitch:

Interior Zone End ZoneWindward Leeward Windward Leeward

GCpf 0.21 -0.43 0.27 0.53GCpi 0.18 0.18 0.18 0.18p (psf) 0.6 -12.9 1.9 -15.0

proof = [13.5(L-X) + 16.9(X)] / L

= [13.5(18 ft) + 16.9(6 ft)] / 24

= 14.4 psf

Calculate the lateral load on the roof diaphragm:

The roof diaphragm will take load from half the wall below and load directly applied to the diaphragm.

WRD = 20.9(5 ft) + 14.4(10 ft)

= 249 plf

Calculate load into the shear wall:


vRD = 600 plf / 2.0 (3/8 nominal panel thickness, 2" nominal width framing, and Case 1)

vRD = 300 plf

Maximum sidewall length:

LMax = [300 (24 ft)] / [249 plf / 2]

= 57 ft (rounded down from 57.8 ft)

b) Maximum roof diaphragm length shall not exceed 80' (WFCM limitation):

LMax = 80 ft

c) Calculate maximum roof diaphragm length based on aspect ratio limits:

LMax = 24(3)

= 72 ft

The maximum roof diaphragm length is:

LMax = 57 ft (WFCM Table 3.16A1)


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PRESCRIPTIVE DESIGN


Table 3.16B Floor Diaphragm Limits for Wind

Description: Minimum and maximum floor diaphragm lengths for given floor diaphragm widths and wind speeds based on floor diaphragm limitations.

Procedure: Using the procedures from Chapter 2 for calculating wind loads, determine the minimum and maximum floor dia-phragm lengths permitted based on floor diaphragm capacity.

Background: Capacities for horizontal unblocked diaphragm assemblies are tabulated based on a nominal panel thickness of 15/32", 8d common nails, 6" nail spacing at dia-phragm boundaries, and supported panel edges.

Example: Given – 150 mph, Exposure B, 11' tributary wall height (2(10'/2) stud wall height + 1' floor joist depth), and 36' floor diaphragm width.

Floor Diaphragm

36 �Floor Diaphragm

Width

FloorDiaphragmLength

The minimum diaphragm aspect ratio limit is equal to 0.33 (1:3) and the maximum diaphragm aspect ratio limit is equal to 3.0 (3:1).

Calculation of Minimum Floor Diaphragm Length

Calculate minimum floor diaphragm length, LMin, based on maximum value obtained from the following two calculations:

a) Calculate the floor diaphragm length required based on wind load acting parallel to the ridge:

Floor diaphragm load: WFD = 171 plf (Table 2.5B)Calculate load into shear wall:

From floor diaphragm:

V = [171 plf (36 ft)] / 2

= 3,078 lbs

Using 2015 SDPWS Table 4.2C Nominal Unit Shear Ca-pacities for Wood-Frame Diaphragms (unblocked) and applying the (1/2.0) ASD reduction factor per SDPWS Section 4.2.3 and specific gravity adjustment factor [1 – (0.5 – G)] for G = 0.42 (Footnote 2 Table 4.2C): vFD = 505 plf [1 – (0.5 – 0.42)] / 2.0 (Case 3)

vFD = 232 plf

Minimum floor diaphragm length: LMin = 3,078 lbs / 232 plf

= 14 ft (rounded up from 13.3 ft)

b) Calculate the minimum floor diaphragm length needed based on aspect ratio limits: LMin = 36 ft / 3

= 12 ft

The minimum floor diaphragm length is: LMin = 14 ft (WFCM Table 3.16B)


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Calculation of Maximum Floor Diaphragm Length

Calculate the maximum floor diaphragm length, LMax, based on the minimum value obtained from the following three calculations:

a) Calculate floor diaphragm length based on the wind load acting perpendicular to the ridge:

Floor diaphragm load: WFD = 251 plf (Table 2.5A)

Calculate load into shear wall:

Using 2015 SDPWS Table 4.2C Nominal Unit Shear Ca-pacities for Wood-Frame Diaphragms (unblocked) and applying the (1/2.0) ASD reduction factor per SDPWS Section 4.2.3 and specific gravity adjustment factor [1 – (0.5 – G)] for G = 0.42 (Footnote 2 Table 4.2C): vFD = 670 plf [1 - (0.5 - 0.42)] / 2.0 (Case 1)

vFD = 308 plf

Maximum sidewall length:

LMax = [308 (36 ft)] / [251 plf / 2]

= 88.4 ft

b) Maximum floor diaphragm length shall not exceed 80 ft (WFCM limitation): LMax = 80 ft

c) Calculate maximum floor diaphragm length based on aspect ratio limits: LMax = 36 (3)

= 108 ft

The maximum roof diaphragm length is: LMax = 80 ft (WFCM Table 3.16B)


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Tables 3.16C1-C3 Diaphragm Limits for Seismic

Description: Maximum diaphragm dimension, L, for seismic.

Procedure: Using shear loads at each level, calcu-lated in accordance with Table 2.6 and Commentary to Table 2.6, determine the maximum diaphragm dimension, L, for seismic such that the allowable unit shear capacity of the reference diaphragm con-struction is not exceeded.

Background: Tabulated requirements for maximum diaphragm dimension, L, are provided for the reference unblocked diaphragm construction in the WFCM. The aspect ratio of the diaphragm is limited to 3:1 and a maximum dimension, L, not to exceed 80 ft.

Dead Load Assumptions: Roof/Ceiling = 15 psf, Floor = 12 psf, Partition = 8 psf, Wall = 110 plf; Ground Snow Load = 30 psf; Lateral force resisting system: wood structural panel shear walls.

Example: Given – Two-story building above grade plane with rectangular dimensions of 36' x 80' and Seismic Design Category C.

Roof/Ceiling

For roof diaphragm construction of 3/8" wood structural panel sheathing (unblocked), 8d common nails ‐ 6" edge spacing:

Using 2015 SDPWS Table 4.2C Nominal Unit Shear Ca-pacities for Wood-Frame Diaphragms (unblocked) and applying the (1/2.0) ASD reduction factor per SDPWS Section 4.2.3:

vRD = 430 plf / 2.0 (Case 1)

vRD = 215 plf

The effective seismic weight resisted by the roof/ceil-ing diaphragm assuming loading perpendicular to the L dimension:

WRD = Wroof + W(wall L)/2 + Wpartition/2 + Wgable

= 75,120 lbs

where:

Wroof = weight of the roof which includes consideration of 2′ overhangs

= 15 psf [(36 ft + 4 ft) x (80 ft + 4 ft)]

= 50,400 lbs

W(wall L) = weight of exterior walls in the L dimension

110 plf (80 ft + 80 ft) = 17,600 lbs

Wpartition = weight of partition walls

= 8 psf (36 ft) (80 ft) = 23,040 lbs

Wgable = weight of the gable end wall

= 110 plf (2) (1/2) (80 ft) / 2 = 4,400 lbs

V = (75,120 lbs) (1.1) (SDS/R) (0.7) = 4,450 lbs

v = 4,450lbs / (2W) = 62 plf

Factor for 2 story: 62/0.92 = 67 plf

67 plf < 215 plf OK

Maximum diaphragm dimension, L, tabulated = 80 ft (WFCM Table 3.16C1)

Diaphragm load ratio = 67/215 = 0.31 (WFCM Table 3.16C1)

Floor

For floor diaphragm construction of 15/32" wood structural panel sheathing (unblocked), G = 0.42 framing, 8d com-mon nails ‐ 6" edge spacing:

Using 2015 SDPWS Table 4.2C Nominal Unit Shear Ca-pacities for Wood-Frame Diaphragms (unblocked) and applying the (1/2.0) ASD reduction factor per SDPWS Section 4.2.3:

vFD = 480 plf / 2.0 (Case 1)

vFD = 240 plf

Specific Gravity Adjustment Factor = [1 - (0.5 - G)] = 0.92 (SDPWS Table 4.2C Footnote 2)

vFD = 240 plf x 0.92 = 221 plf


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The effective seismic weight resisted by the floor diaphragm assuming loading perpendicular to the L di-mension:

WFD = Wfloor + +W(wall W)/2 + W(wall L) + Wpartition

= 79,160 lbswhere:

Wfloor = weight of the roof which includes consideration of 2′ overhangs

= 12 psf (36 ft) (80 ft) = 34,560 lbs

W(wall W) = weight of exterior walls in W dimension

= 110 plf (36 ft + 36 ft) = 7,920 lbs

W(wall L) = weight of exterior walls in L dimension

110 plf (80 ft + 80 ft) = 17,600 lbs

Wpartition = weight of partition walls

= 8 psf (36 ft) (80 ft) = 23,040 lbs

V = (79,160 lbs ) (1.1) (SDS/R) (0.7) = 4,689 lbs

v = 4,689 lbs / (2W) = 65 plf

Factor for 2-story: 65/0.92 = 71 plf

71 plf < 221 plf OK

Maximum diaphragm dimension, L, tabulated = 80 ft

(WFCM Table 3.16C1)

Diaphragm load ratio = 71/221 = 0.32

(WFCM Table 3.16C1)

Footnote 1The tabulated requirements are based on reference con-struction of roof and floor diaphragms with long dimension of panels perpendicular to framing members and joints staggered (i.e. Case 1, unblocked diaphragm per SDPWS).

Footnote 2Tabulated maximum length requirements can be adjusted to determine the maximum length for other cases. The ref-erence case is for 3-story construction, floor weights = 12 psf, roof/ceiling = 15 psf, partition = 8 psf, and wall=110 plf. The maximum aspect ratio of unblocked diaphragms is limited to 3:1 and L is limited to 80 ft.

Footnote 3The diaphragm load ratio is used to account for other than reference conditions associated with the tabulated load ratio.

The number of stories factor accounts for vertical distribu-tion factors associated with 1, 2, and 3 story buildings in accordance with ASCE 7-16. The reference case for Table 3.16C is a three-story building, hence, the adjustment for three-story is 1.0. Reduced shears are associated with two-story and one-story buildings. The two-story factor of 0.92 results from the ratio of 1.1/1.2 and the one-story factor of 0.83 results from the ratio of 1.0/1.2 (see WFCM Commentary to Table 2.6).

Tabulated requirements are based on use of the reference vertical system which is wood frame walls sheathed with wood structural panels. Where other sheathing materials are used, increased seismic loads are applicable in propor-tion to the ratio of the applicable seismic R values (See Commentary to Table 3.3).

The diaphragm shear adjustment factor allows for adjust-ment of unit shear loads for other common load cases that may involve larger roof weight, floor weight, or wall weight than used for the reference conditions used in the tabulated requirements. Adjustment of tabulated values for other than the reference condition weights (denoted by the column of factors equal to 1.0) is by use of factors that account for the increase in forces for different weight materials. The largest applicable increase factor for a given building dimension W is tabulated rather than providing adjustment factors that vary by building aspect ratio.

Assuming all weights remained unchanged in the prior example except that roof weight is increased from 15 psf to 25 psf, an increase in shear load would result and could be calculated directly as follows:

WRD = Wroof + W(wall L)/2 + Wpartition/2 + Wgable

= 108,720 lbswhere:

Wroof = weight of the roof which includes consideration of 2′ overhangs

= 25 psf [(36 ft + 4 ft) (80 ft + 4 ft)]

= 84,000 lbs

V = (108,720) (1.1) (SDS/R) (0.7) = 6,440 lbs

v = 6,440 lbs / (2W) = 90 plf

Factor for 2-story: 90/0.92 = 98 plf

98 plf < 215 plf OK


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PRESCRIPTIVE DESIGN


Ratio: V(25 psf roof)/V(15 psf roof

= 98 plf / 67 plf

= 1.46 (WFCM Table 3.3 Footnote 3)

Footnote 4Requirements are tabulated for ground snow load con-ditions of 30 psf, 50 psf, and 70 psf. Effective seismic weight includes 20% of ground snow load where ground snow load exceeds 30 psf. For 50 psf and 70 psf tables, effective seismic weight at the roof is increased by 10 psf and 14 psf to account for snow.

Values of SDS are associated with the upper boundaries of SDC A, B, C, D0, D1, and D2 used to tabulate requirements.


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Figure W4.1 Roof and Ceiling Framing - Finished Attic Details

Cross Section (East Section)

Roof Framing Plan (East Section)

Ceiling Framing Plan (East Section)

FINISHED ATTIC


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Figure W4.2 Roof and Ceiling Framing – Raised Ceiling Details

Cross Section (West Section)

Roof Framing Plan (West Section)

Ceiling Framing Plan (West Section)


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Ceiling Framing – Finished Attic

Floor Joists (WFCM 3.3.1.1) For habitable attics, use residential sleeping area with 30psf live load, choose floor joists from Table

3.18A: Live Load: ................................................................................................... 30 psf Dead Load: .................................................................................................. 10 psf Joist Vertical Displacement L/Δ: ............................................................... 360 Required Span: ............................................................................................ 16 ft Table W4.3 Selection of Specie, Grade, Size, and Spacing for Floor Joists: (Table 3.18A)

Specie Douglas Fir-Larch Hem-Fir Southern Pine Spruce-Pine-Fir

Spacing 16" 16" 16" 16"

Grade #2 #2 #2 #2

Size 2x10 2x10 2x12 2x10

Maximum Span 17'-5" Ok 16'-10" Ok 18'-6" Ok 17'-2" Ok Floor Sheathing (WFCM 3.3.4.1) Choose floor sheathing from Table 3.14: Floor Joist Spacing:..................................................................................... 16 in. Sheathing Type (Wood Structural Panel or Board Sheathing): .................. WSP Single Floor Span Rating or Grade: ................................................................................ 16 o.c. Tabulated Minimum Panel Thickness: ....................................................... 19/32 in. Ok Floor Diaphragm Bracing (WFCM 3.1.3.3g, 3.3.5, and Figure 3.7b) WFCM 3.3.5 prescribes floor diaphragm bracing in the first two bays at four feet on center for

wind speeds greater than 130 mph. Nailing requirements are per Table 3.1.

Blocking to Joist (toe-nailed): 2-8d Common


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Roof and Ceiling Sheathing

Sheathing (WFCM 3.5.4.1) Choose Roof Sheathing from Tables 3.12A and 3.12B: Ground Snow Load .............................................................................. 30 psf Live Load .......................................................................................... 20 psf Dead Load .......................................................................................... 10 psf Three second gust wind speed (700 yr) and exposure category: .......... 160 mph Exp. B Rafter/Truss Spacing: ........................................................................... 16 in. Sheathing Type: .................................................................................... WSP Sheathing Grade/OSB Tabulated Minimum Panel Thickness: From Table 3.12A (wind): .......................................................... 24/0 (3/8) in. Ok From Table 3.12B (live and snow): ........................................... 24/0 (3/8) in. Ok

Roof Diaphragm Bracing – Finished Attic (WFCM 3.1.3.3g and 3.5.5) WFCM 3.5.5 prescribes roof diaphragm bracing in the first two bays at four feet on center. However, the Exception in WFCM 3.5.5 permits roof diaphragm blocking to be omitted if the attic floor is used to brace the gable end wall which is what was prescribed in WFCM 3.3.5 (see p. 18).


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3.3.4.2 Sheathing Edge Support Edges of floor sheathing shall have approved

tongue-and-groove joints or shall be supported with block-ing, unless ¼ inch minimum thickness underlayment or 1½ inches of approved cellular or lightweight concrete is installed, or unless the finish floor is of ¾ inch wood strip.

3.3.5 Floor Diaphragm Bracing

For 3-second gust wind speeds greater than 130 mph (See Figure 1.1), blocking and connections shall be provid-ed at panel edges perpendicular to floor framing members in the first two bays of framing and shall be spaced at a maximum of 4 feet on center. Nailing requirements are given in Table 3.1 (see Figure 3.7b).

3.4 Wall Systems

3.4.1 Exterior Walls

3.4.1.1 Wood Studs Wall studs shall be in accordance with the maximum

spans for common species and grades of wall studs speci-fied in Tables 3.20A-B and spaced in accordance with Table 3.20C. Exterior loadbearing studs shall be limited to a height of 10 feet or less between horizontal supports as specified in Table 3.20C. Exterior non-loadbearing studs shall be limited to a height of 14 feet or less for 2x4 studs and 20 feet or less for 2x6 and 2x8 studs in accordance with Table 3.20C.

3.4.1.1.1 Notching and Boring Notches in either edge of studs shall not be located in the middle one-third of the stud length. Notches in the outer thirds of the stud length shall not exceed 25% of the actual stud depth. Bored holes shall not exceed 40% of the actual stud depth and the edge of the hole shall not be closer than 5/8 inch to the edge of the stud (see Figure 3.3b). Notches and holes shall not occur in the same cross-section.

EXCEPTION: Bored holes shall not exceed 60% of the actual stud depth when studs are doubled.

3.4.1.1.2 Stud Continuity Studs shall be continuous between horizontal supports, including but not limited to: girders, floor diaphragm assemblies, ceiling diaphragm assemblies, and roof diaphragm assemblies. When attic floor diaphragm or ceiling diaphragm assemblies are used to brace gable endwalls, the sheathing and fasteners shall be as specified in Table 3.15. The framing and connections shall be capable of transferring the loads into the ceiling or attic floor diaphragm (see Figures 3.7a-b).

3.4.1.1.3 Corners A minimum of three studs shall be provided at each corner of an exterior wall (see Figures 3.8a-b).

EXCEPTION: Reduced stud requirements shall be permitted provided shear walls are not con-tinuous to corners. Framing must be capable of

transferring axial tension and compression loads from above and providing adequate backing for the attachment of sheathing and cladding materi-als.

3.4.1.2 Top Plates Double top plates shall be provided at the top of all

exterior stud walls. The double plates shall overlap at corners and at intersections with other exterior or interior loadbearing walls (see Figure 3.8d). Double top plates shall be lap spliced with end joints offset in accordance with the minimum requirements given in Table 3.21.

3.4.1.3 Bottom Plates Bottom plates shall not be less than 2 inch nominal

thickness and not less than the width of the wall studs. Studs shall have full bearing on the bottom plate.

3.4.1.4 Wall Openings Headers shall be provided over all exterior wall open-

ings. Headers shall be supported by wall studs, jack studs, hangers, or framing anchors (see Figures 3.9a-b).

3.4.1.4.1 Headers Maximum spans for common species of lumber headers and structural glued laminated timber beams used in exterior loadbearing walls shall not exceed the lesser of the applicable spans given in Tables 3.22A-E and Table 3.23A. Maximum spans for common species of lumber headers used in exterior non-loadbearing walls shall not exceed spans given in Table 3.23B.

3.4.1.4.2 Full Height Studs Full height studs shall meet the same requirements as exterior wall studs selected in 3.4.1.1 (see Figures 3.9a-b). The minimum number of full height studs at each end of the header shall not be less than half the number of studs replaced by the opening, in accordance with Table 3.23C.

EXCEPTION: The minimum number of full height studs at each end of the header shall be permitted to be reduced in accordance with Table 3.23D. The capacity of the connection of the top


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EXCEPTION: Where ceiling joists are attached directly to rafters, the combined bearing thick-ness of the ceiling joist and rafter shall be used to determine the depth to thickness ratio.

3.5.1.4 Ridge Beams Ridge beams shall be installed at roof peaks. Ridge

beams shall be in accordance with the maximum spans for common species of lumber beams and structural glued laminated timber beams specified in Table 3.29. Rafters shall bear directly on the ridge beam or be supported by hangers or framing anchors (see Figure 3.10a). Ceiling joists or rafter ties shall not be required where a ridge beam is provided.

EXCEPTION: A ridge board shall be permit-ted to be substituted for a ridge beam when roof slopes equal or exceed 3 in 12. The ridge board shall be at least 1 inch nominal in thickness and not less than the depth of the cut end of the rafter. The rafters shall be placed directly opposite each other. Ceiling joists or rafter ties shall be used to provide a continuous tie between exterior walls. Ceiling joist/rafter tie to rafter connections shall be in accordance with Tables 3.9. Prescriptive solu-tions for ceiling joist/rafter tie to rafter connections are provided in Table 3.9A (see Figures 3.10b-c).

3.5.1.5 Hip and Valley Beams Hip and valley beams shall be in accordance with

the maximum spans (horizontal projection) for common species of lumber hip and valley beams specified in Table 3.28, respectively (see Figures 3.12a-c).

3.5.1.6 Ceiling Joists Ceiling joists shall be in accordance with the maxi-

mum spans for common species of solid sawn ceiling joists specified in Tables 3.25A-B, and shall be braced in accordance with 3.3.1.4.

3.5.1.7 Open Ceilings When ceiling joists and roof ties are omitted and the

rafters are used to create an open (cathedral) ceiling, rafter ends shall be supported on bearing walls, headers, or ridge beams. Rafters shall be attached to the support at each end in accordance with 3.2.

3.5.1.8 Roof Openings Trimmers and headers shall be doubled when the

header span exceeds 4 feet. Headers more than 6 feet in length shall be supported at the ends by rafter hangers or framing anchors unless they bear on a partition, beam, or

wall. Tail rafters which exceed 12 feet in length shall be supported on framing anchors (see Figures 3.11a-c). Nail-ing requirements are given in Table 3.1.

3.5.2 Wood I‑Joist Roof Systems

Wood I-joist rafter systems shall meet the requirements of 2.5.2.

3.5.3 Wood Roof Truss Systems

Wood roof truss systems shall meet the requirements of 2.5.3. See Table 3.27 for representative metal plate connected wood roof truss span tables. Actual design spans will vary by truss manufacturer as a result of specific design conditions.

3.5.4 Roof Sheathing

3.5.4.1 Sheathing Roof sheathing shall be in accordance with the

minimum requirements of Tables 3.12A and 3.12B.

3.5.4.2 Sheathing Edge SupportEdges of all 3/8-inch wood structural panel roof

sheathing, or 7/16-inch wood structural panel roof sheath-ing supported at 24 inches on center, shall be supported with blocking or edge clips.

3.5.5 Roof Diaphragm Bracing

For 3-second gust wind speeds greater than 130 mph (See Figure 1.1) blocking and connections shall be provid-ed, at panel edges perpendicular to roof framing members in the first two bays of framing, and shall be spaced at a maximum of 4 feet on center. Nailing requirements are given in Table 3.1 (see Figure 3.7b).

EXCEPTION: When an attic floor or ceiling diaphragm is used to brace the gable endwall or when a hip roof system is used, additional roof diaphragm blocking is not required.


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Roof Diaphragm Bracing – Raised Ceiling (WFCM 3.5.5 and 3.4.1.1.2) Blocking at 4 ft o.c. in first two rafter bays with full height studs on second floor end wall

framing is possible with balloon framing. The stud length of 12.1 ft to the raised ceiling plus

maximum gable height of 6.2 ft at the ridge gives 18.3 ft which is less than the 20 ft

maximum non-loadbearing stud height (3.1.3.3a). Balloon framed studs would have to be

designed for wind loads.

OR Bracing Gable Endwall with Attic Floor/Ceiling Sheathing Length from Table 3.15 with Gable

Brace Figure 3.7a. Three second gust wind speed (700 yr) and exposure category: ................. 160 mph Exp. B Roof Pitch: ................................................................................................... 7:12 Roof (diaphragm) Span (see raised ceiling calculations): ........................... 21.3 ft Diaphragm Length Available: ..................................................................... 14.5 ft Sheathing Type (wood structural panels or gypsum): ................................. WSP GYP Tabulated Min. Length of Attic Floor/Ceiling Diaphragm (interpolated): .. 7.1 ft 18.5 ft Bracing One Gable End Adjustment (Footnote 1): ..................................... 0.84 0.84 Wall Height Adjustment (Footnote 2): (13.1'/10') .................................... 1.31 1.31 Ceiling Framing Spacing Adjustment (Footnote 4): ................................... 1.0 0.78 Required Minimum Length of Attic Floor/Ceiling Diaphragm: Tabulated Minimum Length x Applicable Adjustment Factors: .......... 7.8 ft Ok 15.9 ft NG

WSP sheathing is required for the ceiling diaphragm since 15.9' required length of gypsum diaphragm is greater than the 14.5' length of the raised ceiling.

RAFTERSS

Endwall Blocking Detail (Floor or Roof) – floor blocking shown


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PRESCRIPTIVE DESIGN

Table 3.15 Minimum Attic Floor/Ceiling Length When Bracing Gable Endwall for Wind Loads

90 95 100 105 110 115 120 130 140 150 160 170 180 195

Roof Span (ft)

12 4 4 4 4 4 4 4 4 4 4 4 4 4 424 8 8 8 8 8 8 8 8 8 8 8 8 8 836 12 12 12 12 12 12 12 12 12 12 12 12 12 1312 4 4 4 4 4 4 4 4 4 4 4 4 4 424 8 8 8 8 8 8 8 8 8 8 8 8 8 936 12 12 12 12 12 12 12 12 12 12 12 12 12 1412 4 4 4 4 4 4 4 4 4 4 4 4 4 524 8 8 8 8 8 8 8 8 8 8 8 8 8 936 12 12 12 12 12 12 12 12 12 12 12 12 12 1412 4 4 4 4 4 4 4 4 4 4 4 4 4 524 8 8 8 8 8 8 8 8 8 8 8 8 8 936 12 12 12 12 12 12 12 12 12 12 12 12 13 1512 4 4 4 4 4 4 4 4 4 4 4 4 4 524 8 8 8 8 8 8 8 8 8 8 8 8 8 1036 12 12 12 12 12 12 12 12 12 12 12 12 14 1612 4 4 4 4 4 4 4 4 4 4 4 4 4 524 8 8 8 8 8 8 8 8 8 8 8 8 9 1036 12 12 12 12 12 12 12 12 12 12 12 13 14 1712 4 4 4 4 4 4 4 4 4 4 4 4 4 524 8 8 8 8 8 8 8 8 8 8 8 8 9 1036 12 12 12 12 12 12 12 12 12 12 12 13 15 1712 4 4 4 4 4 4 4 4 4 4 4 4 4 524 8 8 8 8 8 8 8 8 8 8 8 8 9 1136 12 12 12 12 12 12 12 12 12 12 12 14 15 1812 4 4 4 4 4 4 4 4 4 4 4 4 4 524 8 8 8 8 8 8 8 8 8 8 8 8 9 1136 12 12 12 12 12 12 12 12 12 12 13 14 16 1912 4 4 4 4 4 4 4 4 4 4 4 4 4 524 8 8 8 8 8 8 8 8 8 8 8 9 10 1136 12 12 12 12 12 12 12 12 12 12 13 15 17 2012 4 4 4 4 5 5 5 6 7 8 9 10 11 1324 8 8 8 8 9 9 10 12 14 16 18 20 23 2636 12 12 12 12 13 15 16 19 22 25 28 32 35 4112 4 4 4 4 5 5 5 6 7 8 9 10 12 1424 8 8 8 8 9 10 11 12 14 16 19 21 23 2736 12 12 12 13 14 16 17 20 23 26 30 33 37 4412 4 4 4 4 5 5 6 6 7 8 10 11 12 1424 8 8 8 9 9 10 11 13 15 17 19 22 24 2936 12 12 13 14 15 16 18 21 24 28 31 35 40 4612 4 4 4 4 5 5 6 7 8 9 10 11 12 1424 8 8 8 9 10 11 12 13 16 18 20 23 25 3036 12 12 13 15 16 17 19 22 25 29 33 37 42 4912 4 4 4 5 5 5 6 7 8 9 10 11 12 1424 8 8 8 9 10 11 12 14 16 18 21 24 26 3136 12 13 14 15 17 18 20 23 27 31 35 39 44 5112 4 4 4 5 5 5 6 7 8 9 10 11 13 1524 8 8 9 10 11 11 12 14 17 19 22 24 27 3236 12 13 15 16 17 19 21 24 28 32 36 41 46 5412 4 4 4 5 5 6 6 7 8 9 10 12 13 1524 8 8 9 10 11 12 13 15 17 20 22 25 28 3336 12 14 15 17 18 20 22 25 29 34 38 43 48 5612 4 4 4 5 5 6 6 7 8 9 11 12 13 1524 8 9 9 10 11 12 13 15 18 20 23 26 29 3436 13 14 16 17 19 21 23 26 31 35 40 45 50 5912 4 4 4 5 5 6 6 7 8 9 11 12 13 1624 8 9 10 11 12 13 14 16 18 21 24 27 30 3536 13 15 16 18 20 22 24 28 32 36 41 47 52 6112 4 4 5 5 5 6 6 7 8 10 11 12 14 1624 8 9 10 11 12 13 14 16 19 22 25 28 31 3636 14 16 17 19 21 23 24 29 33 38 43 49 54 64

See footnotes 1-4.

Length of Ceiling Diaphragm (ft)1,2,3

(measured perpendicular to gable endwall)

12:12

1.5:12-3:12

4:12

5:12

1.5:12 -3:12

9:12

10:12

8:12

7:12

11:12


(See Figure 1.1)

Roof Pitch

5:12

6:12

Assemblies

4:12

Sheathing Grade: Sheathing and Single-Floor

Attic Floor or Ceiling Diaphragm Bracing Gable Endwall(Wind Parallel to Ridge)

12:12

GypsumCeiling Diaphragm

Bracing Gable Endwall(Wind Parallel to Ridge)4

7:12

8:12

9:12

10:12

6:12

11:12


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1

2

3

4 Tabulated gypsum ceiling requirements shall be permitted to be multiplied by 0.78 when ceiling framing is spaced at 16 inches o.c. or less.

Attic floor or ceiling diaphragms are not required for hip roof systems.

Tabulated attic floor or ceiling length requirements assume sheathing continuous from gable‐end to gable‐end. For an attic floor or ceiling bracing only one gable‐end, the tabulated length requirement shall be permitted to be multiplied by 0.84. In no case shall the length requirement be less than one‐third of the distance between bracing walls for gypsum ceilings or one‐third of the distance for attic floors or ceilings sheathed with structural sheathing.

Tabulated length requirements are based on 10 foot wall heights. For other wall heights, H, the tabulated length requirements shall be multiplied by (H+1)/10.

Footnotes to Table 3.15


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Table 3.15 Minimum Attic Floor/Ceiling Length when Bracing Gable Endwall for Wind Loads

Description: Minimum length of sheathing required from gable end on attic floor or ceiling.

Procedure: Using loads calculated from Chapter 2, determine the minimum sheathing length required to brace the gable end wall against those loads.

Background: Capacities for horizontal unblocked dia-phragm assemblies are tabulated based on sheathing thickness, nail size, and panel edge nailing.

Example:Given - 150 mph, Exposure B, 6:12 roof pitch, 24' roof span, G = 0.42, Unblocked diaphragm.

Determine the length of sheathing required using wood structural panels:

Lateral diaphragm load from wind parallel to ridge:

From WFCM Table 2.5C: w = 101 plf

Calculate load into the floor / ceiling diaphragm: V = 101 plf (24 ft)

= 2,424 lbs


Capacity of structural sheathing: v = 505/(2.0) (15/32 nominal panel thickness,

2" nominal width framing, and Cases 2, 3, 4, 5, 6)

= 252.5 plf

Adjusting for specific gravity of framing per 2015 SDPWS Table 4.2C Footnote 2: v = 252.5 plf [1 - (0.5 - G)]

= 252.5 [0.92] plf

= 232 plf

Required structural sheathing attic floor or ceiling dia-phragm length: L = [2,424 lbs / 2] / 232 plf

= 5.2 ft

Given a maximum diaphragm aspect ratio of 3:1 for un-blocked diaphragms per SDPWS Table 4.2.4, for a building end wall width (roof span) equal to 24', the minimum length of attic floor/ceiling diaphragm is 8'.

(WFCM Table 3.15)

Determine the required attic floor/ceiling diaphragm length using Gypsum Wallboard:

From WFCM Supplement Table S-3:

ASD Unit Shear Capacity of gypsum wallboard: v = 70 plf

Required attic floor/ceiling diaphragm length using gyp-sum wallboard: L = [2,424 lbs / 2] / 70 plf

= 18 ft (rounded up from 17.3 ft) (WFCM Table 3.15)

Footnote 1:See Commentary for Table 2.5C Footnote 3 for calcula-tions.

Footnote 4:From Supplement Table S-3 Footnote 1:

For ceiling framing at 16" o.c. or less, the tabulated capac-ity for gypsum wallboard is 90 plf.

Dividing the tabulated capacity by the increased capacity: = 70 plf / 90 plf

= 0.78 (WFCM Table 3.15)


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ENG

INEER

ED

DES

IGN


2

Table 2.5C Lateral Diaphragm Loads from Wind - Parallel to Ridge (For Attic Floor or Ceiling Diaphragm When Bracing Gable Endwall)

w

A�c Floor / Ce i lingDiaphrag m

a�c floor / ceiling

Tribut ary Area of Ce i ling Diaphrag m

W IND

See footnotes 1 - 8.

90 95 100 105 110 115 120 130 140 150 160 170 180 195

Roof Span (ft)24 58 58 58 58 58 58 58 67 78 89 102 115 129 15136 61 61 61 61 61 61 61 71 82 94 107 121 135 15948 65 65 65 65 65 65 65 75 87 100 113 128 144 16860 69 69 69 69 69 69 69 79 92 105 120 135 152 17824 60 60 60 60 60 60 60 70 81 93 106 120 134 15736 65 65 65 65 65 65 65 75 87 100 113 128 144 16848 70 70 70 70 70 70 70 81 94 107 122 138 155 18160 75 75 75 75 75 75 75 86 100 115 131 148 166 19424 63 63 63 63 63 63 63 73 84 97 110 125 140 16436 69 69 69 69 69 69 69 79 92 105 120 135 152 17848 75 75 75 75 75 75 75 86 100 115 131 148 166 19460 81 81 81 81 81 81 81 94 109 125 142 160 179 21124 65 65 65 65 65 65 65 76 88 101 115 130 145 17036 73 73 73 73 73 73 73 84 97 111 126 143 160 18848 80 80 80 80 80 80 80 92 107 123 140 158 177 20760 88 88 88 88 88 88 88 101 117 134 153 172 193 22724 68 68 68 68 68 68 68 79 91 105 119 135 151 17736 76 76 76 76 76 76 76 88 102 117 133 150 168 19848 85 85 85 85 85 85 85 98 114 130 148 167 188 22060 94 94 94 94 94 94 94 108 125 144 164 185 207 24324 70 70 70 70 70 70 70 82 95 109 124 140 156 18436 80 80 80 80 80 80 80 92 107 123 140 158 177 20748 90 90 90 90 90 90 90 104 120 138 157 177 199 23360 100 100 100 100 100 100 100 115 134 153 174 197 221 25924 73 73 73 73 73 73 73 85 98 113 128 145 162 19036 84 84 84 84 84 84 84 96 112 128 146 165 185 21748 95 95 95 95 95 95 95 109 127 146 166 187 210 24660 106 106 106 106 106 106 106 122 142 163 185 209 235 27524 75 75 75 75 75 75 75 87 101 116 132 150 168 19736 88 88 88 88 88 88 88 101 117 134 153 172 193 22748 100 100 100 100 100 100 100 115 134 153 174 197 221 25960 113 113 113 113 113 113 113 130 150 173 196 222 248 29224 78 78 78 78 78 78 78 90 105 120 137 154 173 20336 91 91 91 91 91 91 91 105 122 140 159 180 201 23648 105 105 105 105 105 105 105 121 140 161 183 207 232 27260 119 119 119 119 119 119 119 137 159 182 207 234 262 30824 80 80 80 80 80 80 80 93 108 124 141 159 179 21036 95 95 95 95 95 95 95 109 127 146 166 187 210 24648 110 110 110 110 110 110 110 127 147 169 192 217 243 28560 125 125 125 125 125 125 125 144 167 192 218 246 276 324

*


(See Figure 1.1)

Roof Pitch

1.5:12 - 3:12

8:12

4:12

Unit Lateral Loads for Attic Floor/Ceiling Diaphragm, wattic floor/ceiling(plf)1,2,3,4,5,6,7,8

See Footnotes 1 -8.

7:12

12:12

5:12

9:12

6:12

10:12

11:12


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Workbook gypsum example: 119plf (21.3') / 2 / 70plf = 18'


ENGINEERED DESIGN

Footnotes to Table 2.5C

Footnotes to Tables 2.5C

1 The total shear load equals the tabulated unit lateral load multiplied by the endwall length. 2 Tabulated unit lateral loads are based on 10 foot wall heights. 3 Tabulated unit lateral loads assume the attic floor/ceiling diaphragm is continuous between endwalls. When

the diaphragm only resists loads from one endwall, the tabulated unit lateral load shall be multiplied by 0.84. 4 Tabulated unit lateral loads are based on MWFRS wind loads and assume a building located in Exposure B

with a mean roof height of 33 feet. For buildings located in Exposures B with mean roof heights less than 33 feet, or in Exposures C and D, tabulated values shall be adjusted in accordance with Section 2.1.3.1.

5 Attic floor or ceiling diaphragms shall not be used to brace gable endwalls used with cathedral ceilings. 6 Attic floor or ceiling diaphragms are not required for hip roof systems. 7 When a ceiling diaphragm is used to brace the gable endwalls, the unit lateral loads on the roof diaphragm,

when the wind is parallel to the ridge, need not exceed the tabulated roof lateral load (from Table 2.5B) minus the ceiling lateral load (from Table 2.5C).

8 Shear capacity requirements for attic floor or ceiling diaphragms shall be calculated as follows:

Calculating

Total Shear Capacity Requirements

Vroof, Vattic floor/ceiling

(lbs)

Calculating Diaphragm

Unit Shear Capacity Requirements

vroof, vattic floor/ceiling

(plf)

/ / ( )attic floor ceiling attic floor ceilingV w B=

ceilingflooratticBfromTableroofroof VVV /)5.2||( −=

)(2/

/ LV

v ceilingflooratticceilingfloorattic =

)(2 LV

v roofroof =


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SU

PPLE

MENT


S

Table S-2 Maximum Spans and Allowable Total Uniform Loads (Deflection) for Roof Sheathing for Roof Live and Snow Loads1 (Cont.)

Panels 24 inches or Wider Continuous Over 2 or More Spans with Long Dimension Perpendicular to Supports

Rafter/Truss Spacing (in.) 12 16 19.2 24

Sheathing Type Span Rating or Grade

Minimum Panel Performance Category

Maximum Rafter/ Truss Spacing (in.)

Allowable Total Uniform Loads (psf) 24/0 3/8 24 2 402 157 91 49 24/16 7/16 24 519 201 115 61 32/16 15/32 24 760 292 164 85 40/20 19/32 24 1,478 562 312 156

Wood Structural Panels (Sheathing Grades, C‐C, C‐D, OSB)1

48/24 23/32 24 2,620 992 547 270 16 o.c. 19/32 24 989 378 211 108 20 o.c. 19/32 24 1,380 526 292 147 24 o.c. 23/32 24 1,968 746 413 205 32 o.c. 7/8 24 4,252 1,606 883 433

Wood Structural Panels (Single Floor Grades,

Underlayment C‐C Plugged, OSB)1

48 o.c. 1‐3/32 24 7,515 2,833 1,555 758

1 Tabulated values are based on deflection criteria of L/240 under live loads and L/180 under total loads (assumed 10 psf for dead loads). 2 Edge supports (tongue‐and groove edges, panel edge clips at midway between supports, lumber blocking, or other) are required. Otherwise,

the maximum spacing is limited to 19.2 inches.

Table S-3 ASD Unit Shear Capacity for Horizontal Diaphragm Assemblies Sheathed with Gypsum Wallboard

Nail Spacing (in.) Sheathing Material

MaterialThickness

(in.) Nail Size

Diaphragm Construction Panel Edges

Intermediate Supports

Recommended ASD Unit Shear Capacity

(plf)

Gypsum Wallboard

1/2 5d Cooler Nails or 1‐1/4 Drywall

Screws Unblocked 7 10 70 1

1 Tabulated shear capacity can be increased to 90 plf when ceiling framing members are spaced not

more than 16 inches on center.

Table S-3 ASD Unit Shear Capacity for Horizontal Diaphragm Assemblies Sheathed with Gypsum Wallboard

Table S-2B Maximum Spans and Allowable Total Uniform Loads (Deflection) for Roof Sheathing for Normal Duration Loads


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AM

ERIC

AN

WO

OD

CO

UNC

IL

LATERAL FORCE-RESISTING SYSTEMS 4

SPECIAL DESIG

N PR

OVISION

S FOR

WIN

D AN

D SEISM

IC

Table 4.2C Nominal Unit Shear Capacities for Wood-Frame Diaphragms

Unblocked Wood Structural Panel Diaphragms1,2,3,4,5

1. Nominal unit shear capacities shall be adjusted in accordance with 4.2.3 to de-termine ASD allowable unit shear capacity and LRFD factored unit resistance. For general construction requirements see 4.2.6. For specific requirements, see 4.2.7.1 for wood structural panel diaphragms. See Appendix A for common nail dimensions.

2. For species and grades of framing other than Douglas-Fir-Larch or Southern Pine, reduced nominal unit shear capacities shall be determined by multiplying the tabulated nominal unit shear capacity by the Specific Gravity Adjustment Factor = [1-(0.5-G)], where G = Specific Gravity of the framing lumber from the NDS (Table 12.3.3A). The Specific Gravity Adjustment Factor shall not be greater than 1.

3. Apparent shear stiffness values, Ga, are based on nail slip in framing with moisture content less than or equal to 19% at time of fabrication and panel stiffness values for diaphragms constructed with either OSB or 3-ply plywood panels. When 4-ply or 5-ply plywood panels or composite panels are used, Ga values shall be permitted to be multiplied by 1.2.

4. Where moisture content of the framing is greater than 19% at time of fabrica-tion, Ga values shall be multiplied by 0.5.

5. Diaphragm resistance depends on the direction of continuous panel joints with respect to the loading direction and direction of framing members, and is independent of the panel orientation.

A

B

Sheathing Grade Common Nail Size

Minimum Fastener

Penetration in Framing

(in.)

Minimum Nominal Panel

Thickness (in.)

Minimum Nominal Width

of Nailed Face at Supported Edges and Boundaries

(in.)

SEISMIC WIND

6 in. Nail Spacing at diaphragm boundaries

and supported panel edges

6 in. Nail Spacing at diaphragm boundaries and

supported panel edges Case 1 Cases 2,3,4,5,6 Case 1 Cases

2,3,4,5,6 vs Ga vs Ga vw vw (plf) (kips/in.) (plf) (kips/in.) (plf) (plf) OSB PLY OSB PLY

Structural I

6d 1-1/4 5/16 2 330 9.0 7.0 250 6.0 4.5 460 350 3 370 7.0 6.0 280 4.5 4.0 520 390

8d 1-3/8 3/8 2 480 8.5 7.0 360 6.0 4.5 670 505 3 530 7.5 6.0 400 5.0 4.0 740 560

10d 1-1/2 15/32 2 570 14 10 430 9.5 7.0 800 600 3 640 12 9.0 480 8.0 6.0 895 670

Sheathing and Single-Floor

6d 1-1/4 5/16 2 300 9.0 6.5 220 6.0 4.0 420 310

3 340 7.0 5.5 250 5.0 3.5 475 350 3/8 2 330 7.5 5.5 250 5.0 4.0 460 350

3 370 6.0 4.5 280 4.0 3.0 520 390

8d 1-3/8

3/8 2 430 9.0 6.5 320 6.0 4.5 600 450 3 480 7.5 5.5 360 5.0 3.5 670 505

7/16 2 460 8.5 6.0 340 5.5 4.0 645 475 3 510 7.0 5.5 380 4.5 3.5 715 530

15/32 2 480 7.5 5.5 360 5.0 4.0 670 505 3 530 6.5 5.0 400 4.0 3.5 740 560

10d

1-1/2

15/32 2 510 15 9.0 380 10 6.0 715 530 3 580 12 8.0 430 8.0 5.5 810 600

19/32 2 570 13 8.5 430 8.5 5.5 800 600 3 640 10 7.5 480 7.0 5.0 895 670

Cases 1&3:Continuous Panel Joints Perpendicular to Framing

Cases 2&4: Continuous Panel Joints Parallel to Framing

Cases 5&6: Continuous Panel Joints Perpen-dicular and Parallel to Framing

Long Panel Direction Perpendicular to Supports

Long Panel Direction Parallel to Supportsa

(a) Panel span rating for out-of-plane loads may be lower than the span rating with the long panel direction perpendicular to supports (See Section 3.2.2 and Section 3.2.3)

Copyright ©

American W

ood Council. D

ownloaded/printed pursuant to License Agreem

ent. No reproduction or transfer authorized.


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2015 SDPWS

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POLLING QUESTION

3. Maximum roof & floor diaphragm lengths in WFCM Tables 3.16A & B are based on?a) Diaphragm capacityb) Maximum prescriptive building dimensionc) Aspect ratio limitsd) All of the abovee) Answers b) and c)




OUTLINE



• Prescriptive Diaphragm Example• Diaphragm Deflection

Equation• Diaphragm Deflection Example• High Load Diaphragms• FAQ• Resources


3-TERM DIAPHRAGM DEFLECTION EQUATION

• Applies to flat and folded (roof) diaphragms.• SDPWS provides tables for a variety of sheathing

material• SDPWS extends to unblocked diaphragms

SDPWS Chapter 4 - Wood Diaphragms



SDPWS Commentary Chapter 4 - Wood Diaphragm



COMPARISON: 3-TERM VS. 4-TERM



SDPWS Commentary Chapter 4 - Wood Diaphragm



COMPARISON: 3-TERM VS. 4-TERM

Shear panel deformation and nail slip4-term 3-term



COMPARISON: 3-TERM VS. 4-TERMApparent Shear Stiffness


4-TERM DEFLECTION



4-TERM DEFLECTION


4-TERM DEFLECTION

Use to calculate en



3-TERM DEFLECTION


3-TERM DEFLECTION



POLLING QUESTION

4. SDPWS has tabulated shear stiffness for which of the following products?a) WSP with screwsb) WSP with nailsc) Lumberd) Gypsum boarde) All of the above except a)


OUTLINE



• Prescriptive Diaphragm Example• Diaphragm Deflection Equation• Diaphragm Deflection

Example• High Load Diaphragms• FAQ• Resources



WOOD DIAPHRAGM DEFLECTION EXAMPLE2015 SDPWS CommentaryEXAMPLE C4.2.2-3 Calculate

Mid-Span Diaphragm Deflection

L=48’16’ 16’

Diaphragm chord joint

W=

24’

Case 1 blocked diaphragm, 7/16” OSB sheathing, 8d common nails at 6”o.c. at all panel edges

A B

Allowable stress design load, =255 plf


WOOD DIAPHRAGM DEFLECTION EXAMPLE2015 SDPWS CommentaryCalculate mid-span deflection for the blocked wood structural panel diaphragm shown in Figure C4.2.2-2. The diaphragm chord splice is sized using allowable stress design loads from seismic while deflection due to seismic is based on strength design loads in accordance with ASCE 7.

Diaphragm apparent shear stiffness, Ga:Ga = 14 kips/in. (SDPWS Table 4.2A)

Diaphragm allowable unit shear capacity for seismic, ns (ASD):ns (ASD) = 255 plf (SDPWS Table 4.2A)

Diaphragm chord: (2) 2x6 No. 2 Douglas Fir-Larch, E = 1,600,000 psi, and G = 0.50



DIAPHRAGM CAPACITY

SDPWS Table 4.2A

Ga = 14 kips/inNominal/2.0 (ASD)vs = 510 plf/2 vs = 255 plf (ASD)


WOOD DIAPHRAGM DEFLECTION EXAMPLE2015 SDPWS CommentaryEXAMPLE C4.2.2-3 Calculate

Mid-Span Diaphragm Deflection

L=48’16’ 16’


W=

24’


A B


vmax=255 plf

Vx= (L/2-x)

x’M = 65,280 ft-lb

Mmax = 73,440 ft-lbM = 65,280 ft-lb

Mx= x(L-x)/2



CHORD SPLICEPart 1Calculate number of 16d common nails in the chord spliceDiaphragm chord:

Two 2x6 No. 2 DFLE = 1,600,000 psiG = 0.50

Z’ASD (NDS Table 12N)= 141 lb. x 1.6 = 226 lb.

16' 16'

Upper plate designed as continuous chord

Splice plates

Joint A Joint B

48'

Wide face of upper top plate. Twelve nails on each side of each joint.


CHORD SPLICEPart 1Calculate number of 16d common nails in the chord spliceThe axial force (T or C) at each joint:

The number of 16d common nails, n, is:



CHORD SPLICEPart 1Calculate number of 16d common nails in the chord spliceMight need to consider Mmax if joint location unknown:

x’M = 65,280 ft-lb

Mmax = 73,440 ft-lbM = 65,280 ft-lb

Mx= x(L-x)/2


MID-SPAN DEFLECTIONPart 2 – Calculate mid-span deflection

Use 3-term equation

4.2-1



MID-SPAN DEFLECTION

Term 1. Deflection due to bending and chord deformation (excluding chord splice slip):

L=48’16’ 16’


W=

24’


A B


𝛿 ,5𝑣𝐿

8𝐸𝐴𝑊

= .

, , . .

0.078𝑖𝑛.

Strength level design loads

ASCE 7 requires that seismic story drift be determined using strength level design loads


MID-SPAN DEFLECTION


L=48’16’ 16’


W=

24’


A B


𝛿 ,5𝑣𝐿

8𝐸𝐴𝑊

= .

, , . .

0.078𝑖𝑛.



MID-SPAN DEFLECTION


L=48’16’ 16’


W=

24’


A B


𝛿 ,5𝑣𝐿

8𝐸𝐴𝑊

= .

, , . .

0.078𝑖𝑛.

Single chord assumption

One top plate designed to resist induced axial force – second as splice plate. Engineering judgment. Doubling area yields 0.04”.


MID-SPAN DEFLECTIONTerm 2. Deflection due to shear, panel shear, and nail slip

Ga = 14 kips/in., apparent shear stiffness (SDPWS Table 4.2A)

𝛿0.25𝑣𝐿1000𝐺

0.25 1.4𝑥255𝑝𝑙𝑓 48𝑓𝑡

100014𝑘𝑖𝑝𝑠

𝑖𝑛 .

0.306𝑖𝑛.



MID-SPAN DEFLECTIONTerm 3. Deflection due to bending chord splice slip

x = 16 ft, distance from the joint to the nearest support. Each joint is located 16 ft from the nearest support



Δc = Joint deformation (in.) due to chord splice slip in each joint.






• 180,000 D1.5 load/slip modulus for dowel type connections per NDS 10.3.6

• Diameter for 16d common NDS Table L4• 180,000 (0.162)1.5 = 11,737 lb/in./nail




Constant of 2 used in numerator to account for slip in nailed splices on each side of joint

𝛥2 𝑇 𝑜𝑟 𝐶

𝛾𝑛2 3,808 𝑙𝑏𝑓

11,737 𝑙𝑏𝑓/𝑖𝑛./𝑛𝑎𝑖𝑙 12 𝑛𝑎𝑖𝑙𝑠

0.054𝑖𝑛



Tension chord slip calculation

0.036 𝑖𝑛.

𝛿 ∑ 16 𝑓𝑡 0.054 𝑖𝑛. 16 𝑓𝑡 0.054 𝑖𝑛.

2 24 𝑓𝑡



MID-SPAN DEFLECTIONTerm 3. Deflection due to bending and chord splice slip

Assume compression chord butt joints have a gap that exceeds the splice slip, so tension chord slip also used for compression chord

Compression chord and total slip calculation

Total deflection due to chord splice slip is:

𝛿 0.036 𝑖𝑛.

𝛿 0.036 𝑖𝑛. 0.036 𝑖𝑛. 0.072 𝑖𝑛.


MID-SPAN DEFLECTION

Total mid-span deflection:

𝛿 0.78𝑖𝑛. 0.306 𝑖𝑛. 0.072 𝑖𝑛. 0.456 𝑖𝑛.



OUTLINE



GE WarehouseOntario, CA


2‐3 people 4‐5 minutes to assemble

Pre‐assemble large sections on the ground

Lift into position with high lift capacity forklifts


Fasten into place


HIGH LOAD DIAPHRAGMS



IBC SPECIAL INSPECTION

1705.5 Wood Construction

1705.5.1 High-load diaphragms

IBC 1705.11 Special Inspection for wind resistance

• 1705.11.1 Structural wood

IBC 1705.12 Special Inspection for seismic resistance

• 1705.12.2 Structural wood


1705.5 WOOD CONSTRUCTION

1705.5.1 High-load Diaphragms• Wood structural panel

• Framing members at adjoining panel edges

• Nails (or staples)



1705.5 WOOD CONSTRUCTIONWood Structural Panels

• Grade and Thickness

Source: APA – The Engineered Wood Association Source: PFS TECO


1705.5 WOOD CONSTRUCTIONWood Structural Panels

Source: APA – The Engineered Wood Association



1705.5 WOOD CONSTRUCTIONNominal size of framing members at adjoining panel edges


NAILS

A few 10d nails…

There are even more!

1705.5 Wood Construction



1705.5 WOOD CONSTRUCTION1705.5.1 High-load Diaphragms

Nail or staple

• Pennyweight

• Diameter (head & shank)

• Length

Ex: 10d common (0.312” head dia. 0.148” shank dia. X 3” shank length)

• Number of fastener lines

• Spacing between fasteners in each line and at edge margins


1705.5 WOOD CONSTRUCTION

Source: AWC – SDPWS & NDS (Table L4)



FASTENER PATTERN – HIGH-LOAD DIAPHRAGMS

Note: Space panel end and edge joint 1/8”. Reduce spacing between lines as necessary to maintain minimum 3/8” fastener edge margin. 3/8” is minimum distance between rows.

Source: AWC – SDPWS Figure 4BTypical Boundary Fastening



Source: AWC – SDPWS Figure 4B




Source: AWC – SDPWS Figure 4B


POLLING QUESTION

5. Inspections on high‐load diaphragms include verifying:

a) Nail diameter, length, and spacing

b) Nominal size of framing members at panel edges

c) Wood structural panel width and depth

d) a and b



OUTLINE




D e m y s t i f y i n g D i a p h r a g m D e s i g n1 0 0

FREQUENTLY ASKED QUESTIONS

Q: How do pneumatic nails affect diaphragm capacity?

A: International Staple, Nail, and Tool Association (ISANTA)

• ICC ES ESR-1539 - Power-Driven Staples and Nails for Use in All Types of Building Construction

• www.isanta.org• https://www.icc-es.org/wp-

content/uploads/report-directory/ESR-1539.pdf




Q: What deflection limits are shown in the code for walls?

A: It depends on the sheathing material•Plaster or Stucco Finishes – L/360 – IBC Table 1604.3•Brittle Finishes – L/240 – IBC Table 1604.3•Flexible Finishes – L/120 – IBC Table 1604.3•Glass –1/175 of glass edge length or 3/4" - IBC Table 2403.3


Flexible vs. Rigid DiaphragmQ: What diaphragm deflection limits are shown in the code?


A: ASCE 7-10

DIAPHRAGM 2 x SHEARWALLS



Flexible vs. Rigid DiaphragmFREQUENTLY ASKED QUESTIONS


ASCE 7-10 Sec. 12.12 DRIFT AND DEFORMATION




ASCE 7-10 Sec. 12.12 DRIFT AND DEFORMATION


Etc…..



Q: Is diaphragm deflection cumulative with shear wall deflection?

A: Yes. Shear walls supporting a horizontal diaphragm would also be evaluated for deflection. Cumulative deflection would then be calculated to determine the maximum anticipated movement to compare with allowables.




Q: Are there provisions to calculate the deflection for a diaphragm that is only partially blocked (i.e. at ends only) or is it proper to base the deflection on the entire diaphragm being unblocked?

A: There are no provisions for a partially blocked diaphragm. Suggest calculating for both a blocked and unblocked diaphragm to determine magnitude of difference and use engineering judgment.



Q: When the nailing pattern in a horizontal diaphragm varies instead of being uniform, how is deflection calculated?A: One approach is to modify the nail-slip constant in the 4-term equation in proportion to the average load on each nail with non-uniform nailing compared to the average load with uniform nailing. APA’s Diaphragm and Shear Wall Design and Construction Guide (L350) provides an example: www.apawood.org.




Q: Is there any benefit if wood structural panels are glued to the assembly?

A: We are not aware of any added benefit with respect to diaphragm deflection.



Q: Is there a multiplier to use for a long-term consideration due to possible enlargement of nail holes or is that all included in the nail slip deflection calculations?

A: Testing done to verify diaphragm deflection calculations is based on full reverse cyclic loads, so the effects of nail hole enlargement has been addressed.




Q: For large diaphragm, what adjustments to deflection equations need to be made to obtain inelastic diaphragm deflection?

A: ASCE 7 Minimum Design Loads for Buildings and Other Structures, Section 12.8.6 includes an amplification factor Cd which is used for story drift and seismic gaps.



Q: What resources are available for designing NLT Diaphragms?

A: Thinkwood Nail-Laminated Timber Design & Construction Guide (U.S. & Canada versions) https://www.thinkwood.com/products-and-systems/mass-timber/nail-laminated-timber




Q: What resources are available for designing CLT Diaphragms?

A: Structurlam Cross Laminated Timber Horizontal Diaphragm Design Example (U.S. & Canada versions) https://www.structurlam.com/resources/manufacturing-standards/


OUTLINE






RESOURCES

www.apawood.org

Publication no. L350


RESOURCES

http://www.amazon.com/Design-Wood-Structures-ASD-LRFD-ebook/dp/B00386MRG8



RESOURCES

http://www.amazon.com/Analysis-Irregular-Shaped-Structures-Diaphragms/dp/007176383X#_

R. Terry Malone, PE, SE –Senior Technical Director WoodWorks

Slides: https://www.woodworks.org/wp-content/uploads/2017-April-Webinar-diaphragms-with-openings.pdf

Recorded Webinar: https://vimeo.com/woodproductscouncil/review/212986898/17ca94ef6f


RESOURCE

American Wood CouncilDavid P. Tyree, P.E., C.B.O. James B. Smith, P.E.Michelle Kam-Biron P.E, S.E., SECB

Structure Magazine

Special Inspection for Wood ConstructionPart 1 – Jan. 2016Part 2 – Feb. 2016

www.structuremag.org



RESOURCE

2015 SEAOC Proceedings

American Wood CouncilDavid P. Tyree, P.E., C.B.O. James B. Smith, P.E.Michelle Kam-Biron P.E, S.E., SECB

www.seaoc.org

Ta l l Wo o d S t r u c t u r e s1 2 0

RESOURCES

www.awc.org• Print versions

• PDF versions



RESOURCES

https://awc.org/pdf/codes-standards/publications/sdpws/StructureMag-SDPWS2015-Changes-1507.pdf

T h i s p r e s e n t a t i o n i s p r o t e c t e d b y U S a n d I n t e r n a t i o n a l C o p y r i g h t l a w s . R e p r o d u c t i o n , d i s t r i b u t i o n , d i s p l a y a n d u s e o f t h e p r e s e n t a t i o n w i t h o u t w r i t t e n p e r m i s s i o n o f A m e r i c a n W o o d C o u n c i l ( A W C ) i s

p r o h i b i t e d . © A m e r i c a n W o o d C o u n c i l 2 0 1 9

in [email protected] | www.awc.org

des431 - demystifying diaphragm design · education systems (aia/ces), provider # 50111237....

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