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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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
-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