USE OF HEADED REINFORCEMENT IN BEAM - COLUMN JOINTS

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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

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HEADEDREINFORCEMENT ?

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

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WHY HEADED REINFORCEMENT ?Congestion/Fabrication/
Placement

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AVAILABLE INFORMATIONAnchorage/Beam-Column Joints

• UCLA Clarkson UniversityWallace, 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)

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PROJECT OVERVIEW

EXTERIOR ROOF CORNER JOINTSEXTERIOR
INTER-STORY JOINTS
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TEST SETUPExterior Roof Connections
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SPECIMEN DETAILSExterior Roof Connections
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DESIGN REQUIREMENTSExterior Roof Connections

• Strong Column - Weak Beam (352-01)
• Joint Confinement Reinforcement (352-01)
• Joint Shear Stress Limits (352-91)

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DESIGN REQUIREMENTSExterior Roof Connections

• Anchorage Requirements
• Tension (318 Eq. 21-5, 352-91)
• Compression (318 S12.3)

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LOAD HISTORYExterior Roof/Inter-Story Connections
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Specimen DamageExterior Roof Connections
KJ16 - Top Bar Pull-out
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REINFORCING DETAILSExterior Roof Connections
Restraint Bars
Restraint Bars
Top View
Side View
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Moment-Rotation ResponseExterior Roof Connections
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MEASURED REBAR STRAINSBeam Top Bars Within the
Joint
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TEST SETUPExterior Inter-Story Connections
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SPECIMEN GEOMETRYExterior Inter-Story Connections
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DESIGN REQUIREMENTSExterior Inter-Story
Connections

• Strong Column - Weak Beam (352-01)
• Joint Confinement Reinforcement (352-01)
• Joint Shear Stress Limits (352-91)

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DESIGN REQUIREMENTSExterior Inter-Story
Connections

• Anchorage Requirements
• Tension (318 Eq. 21-5, 352-91)
• Compression (318 S12.3)

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Beam End RotationExterior Interstory Connections
BCEJ1 - Drift Level 6
Potentiometer
Potentiometer
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MOMENT-ROTATIONExterior Inter-Story Connections
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Specimen DamageExterior Interstory Connections
Bottom Bar Push-Out _at_ 6
BCEJ1 - Drift Level 6
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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

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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 gt 1.2 Joint Shear
  Emdedded Bars Must Be Shoved To Back of Joint
• Practical Recommendation for Emdedment ld
  0.75 ldh

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CONCLUSIONS

• Beam-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