USE OF HEADED REINFORCEMENT IN BEAM - COLUMN JOINTS

John W. Wallace, Ph.D., P.E.Associate Professor, UCLA

Scott W. McConnell, M.S., P.E.Structural Engineer, Schoor-DePalma, NJ

National Science Foundation

Headed Reinforcement Corporation

ERICO Incorporation

HEADEDREINFORCEMENT ?

Plate Anchor Rectangular/Round Threaded/Friction Weld Area = 5 to 10 Bar Area Beam-Column Joints Standard Hooks Ease of Fabrication & Placement

WHY HEADED REINFORCEMENT ?Congestion/Fabrication/Placement

AVAILABLE INFORMATIONAnchorage/Beam-Column Joints UCLA & Clarkson University

Wallace, McConnell, Gupta Reports/ACI Papers (1994, 1997, 1998)Also Yu (2001)

University of Texas, AustinJirsa, Devries, BashandyPh.D. Dissertations (1996), ACI Paper (1999)

University of KansasMcCabe, Wright, Wu (Reports, 1997)

PROJECT OVERVIEW

EXTERIOR ROOF& CORNER JOINTS

EXTERIOR INTER-STORY JOINTS

HYDRAULIC ACTUATOR

LOAD CELL

CLEVIS

52"

HEAVY LINK

SPECIMENLVDT FOR DISPL.CONTROL

RIGID REFERENCEFRAME

36"

TIE DOWN REACTION WALL

STRONG FLOOR

TEST SETUPExterior Roof Connections

SPECIMEN DETAILSExterior Roof Connections

#5 GR60 US REBAR(16 mm)

#3 STIRRUP(9.5 mm)

14.5"

9.5"0.75"

BEAM CROSS SECTION

11" x 16"280 mm x 406 mm

COLUMN CROSS SECTION

16" x 16"406 mm x 406 mm

#6 (20mm)

14.5"

14.5"0.75"

#3 HOOP & CROSSTIES

(368 mm)(241 mm)

DESIGN REQUIREMENTSExterior Roof Connections

Strong Column - Weak Beam (352-01)

Joint Confinement Reinforcement (352-01)

Joint Shear Stress Limits (352-91)

2 (1.1 Test).1 / beamcolumn MM

(test) 51.1/

f/f )1/(3.0

',,

y'c

dreqshprovidedsh

chgcsh

AA

AAshA

0.1 to 5.0 /

kips 140 to 75P ) 60)(25.1)( (

kips 140)"5.13)("16((psi) 4000 )12)(85.0(2

nu

beamsu

n

VV

ksiinAV

V

DESIGN REQUIREMENTSExterior Roof Connections

Anchorage Requirements– Tension (318 Eq. 21-5, 352-91)

– Compression (318 S12.3)

1.55 to 25.122)/14.23 to (18 /

23.14(psi) f/ 900 (0.75)

(psi) f/ 1200 (psi) f/f 02.0'c

'c

'cy

dprovided

bddbd

dbdb

ll

ddll

ddl

1.5 to 23.16.14/22) to 18( /

14.6 (psi) f/925 (psi) f 65/ f 'c

'c

bbdhprovided

bbbydh

ddll

dddl

LOAD HISTORYExterior Roof/Inter-Story Connections

0 200 400 600 800C o u n ter N u m b er

-6

-4

-2

0

2

4

6

Dri

ft L

evel

(%

)

BC EJ -1

Specimen DamageExterior Roof Connections

KJ16 - Top Bar Pull-out

REINFORCING DETAILSExterior Roof Connections

Top View Side View

Restraint Bars Restraint Bars

Moment-Rotation ResponseExterior Roof Connections

-0 .0 6 -0 .0 4 -0 .0 2 0 .0 0 0 .0 2 0 .0 4 0 .0 6

S p ec im en R o ta tio n

-2 5 0 0

-2 0 0 0

-1 5 0 0

-1 0 0 0

-5 0 0

0

5 0 0

1 0 0 0

1 5 0 0

2 0 0 0M

omen

t (in

-kip

s)

-2 5 0

-2 0 0

-1 5 0

-1 0 0

-5 0

0

5 0

1 0 0

1 5 0

2 0 0

Mom

ent (

kN-m

)

K n ee Jo in t # 1 7

4 .0 % 3 .0 %

2 .0 %

1 .5 %

1 .0 %

M n = 1 5 0 8 in -k ip s (P = 4 9 .5 k ip s)

C lo s in g

O p en in g

M n = 1 0 1 1 in -k ip s (P = -3 3 k ip s)

6 .0 %

0 .5 %

MEASURED REBAR STRAINSBeam Top Bars Within the Joint

-2000

0

2000

4000

6000

MIC

RO

ST

RA

IN TB1-FACE

TB1-MID

1.0% 2.0% 4.0%

1.0% 2.0% 4.0%

0 100 200 300 400 500DATA POINT

-2000

0

2000

4000

6000

MIC

RO

ST

RA

IN TB2-FACE

TB2-END

TEST SETUPExterior Inter-Story Connections

12.75 ft (3.89 m)

10 ft(3.05m)

SPECIMEN GEOMETRYExterior Inter-Story Connections

BEAM CROSS SECTION

18" x 24"457 mm x 610 mm

COLUMN CROSS SECTION

18" x 18"457 mm x 457 mm

DESIGN REQUIREMENTSExterior Inter-Story Connections

Strong Column - Weak Beam (352-01)

Joint Confinement Reinforcement (352-01)

Joint Shear Stress Limits (352-91)

2 (1.7 Test).1 / beamcolumn MM

(test) 17.1/

f/f )1/(3.0

',,

y'c

dreqshprovidedsh

chgcsh

AA

AAshA

80.0/

kips 207 ) 60)(25.1)( 79.04(

kips 260)"18)("18((psi) 4000 )15)(85.0(2

nu

columnu

n

VV

VksiinxV

V

DESIGN REQUIREMENTSExterior Inter-Story Connections

Anchorage Requirements– Tension (318 Eq. 21-5, 352-91)

– Compression (318 S12.3)

352)per (0.82 9.06.14/13 /

14.6 (psi) f/925 (psi) f 65/ f 'c

'c

bbdhprovided

bbbydh

ddll

dddl

0.9113/14.23 /

23.14(psi) f/ 900 (0.75)

(psi) f/ 1200 (psi) f/f 02.0'c

'c

'cy

dprovided

bddbd

dbdb

ll

ddll

ddl

Beam End RotationExterior Interstory Connections

BCEJ1 - Drift Level 6%

Potentiometer

Potentiometer

MOMENT-ROTATIONExterior Inter-Story Connections

-0.06 -0.04 -0.02 0.00 0.02 0.04 0.06JOINT ROTATION 24" FROM THE COLUMN FACE

-6000

-4000

-2000

0

2000

4000

6000

MO

ME

NT

(ki

p-i

n)

6 %

4 %

2 %

3 beam bars in tension

4 beam bars in tension

M n= 2860

M n= 3760

Specimen DamageExterior Interstory Connections

BCEJ1 - Drift Level 6% Bottom Bar Push-Out @ 6%

Compression Bar Push-OutExterior Inter-Story Connections

Beam Moment Capacity Compression Steel Slight Pushout Occurs Redistribution From Steel to Concrete Minor Reduction in Beam Moment Capacity Note - Compression ld Satisfied by Checking Tension ld

Summary ObservationsHeaded Bars in Beam-Column Joints

Required Embedment Length Kansas Study: ld = 0.60 ldh Texas Study: ld = (0.60 - 0.70) ldh UCLA/Clarkson Large-Scale Study: ld = 0.82 ldh Other Design Requirements Flexural Strength Ratio: Mcolumn /Mbeam > 1.2 Joint Shear Emdedded Bars Must Be Shoved To Back of Joint Practical Recommendation for Emdedment ld = 0.75 ldh

CONCLUSIONSBeam-Column Joint Tests

– Six Specimens (3 Exterior, 3 Roof)– Small Cover/Need for Transverse Steel– Push-Out of Compression Bars

ACI Committee 352 Draft Report– Modified to Allow Use of Headed Bars

Research Needs - Cyclic Loading– Cover/Transverse Reinforcement– Multiple Layers of Reinforcement