1. Post-Tensioned Precast Concrete Coupling Beams for RC Walls
Brad D. Weldon and Yahya C. Kurama, Ph.D., P.E.
NSF Grant No. NSF/CMS and PCI Daniel P. Jenny Fellowship
Project Start Date: August 1, 2004
Research Objectives:
Develop new system based on experimental and analytical studies
Develop seismic design/analysis guidelines and tools/recommendations for application
Coupled Wall System
beam
PT tendon
connection
region PT
anchor
angle
wall
confinement
Different from conventional systems that use monolithic cast-in-place reinforced concrete coupling beams and embedded steel coupling beams, the lateral resistance of unbonded post-tensioned precast concrete coupling beams develops through the formation of a diagonal compression strut along the span, upon the opening of gaps at the beam-to-wall interfaces.
Coupling System Advantages:
Simpler detailing for the beam and wall piers
Reduced damage to the structure
Self-centering capability
Precast Concrete Advantages:
Single trade construction
Simpler beam-to-wall joint regions
Better fire and environmental protection for the PT tendons
Simpler construction
concrete
wall
precast beam
contact
region
gap
opening
reference line Ca Ta Vb Cb hb ha z Cb Ta Vb Ca lb
Analytical Program
Analytical models of unbonded post-tensioned precast concrete coupling beam subassemblies were developed using the DRAIN-2DX program (Prakash et al. 1993) and the ABAQUS program (Hibbitt, Karlsson, and Sorensen, Inc. 2002). Nonlinear reversed cyclic lateral load analyses of four coupling beam subassemblies were conducted.
Subassembly Properties
DRAIN-2DX Fiber Beam-Column Model
ABAQUS Finite Element Model
Subassem.
Beam Depth, hb mm (in.)
Angle Size
PT Area, Abp
mm2 (in.2)
Varied Parameter 1
711 (28)
L8x8x3/4
1680 (2.60)
prototype beam 2
2240 (3.47)
PT area 3
L8x8x1
angle thickness 4
914 (36)
beam depth
Subassembly 1
Subassembly 2
Principal Tension Stresses Principal Compression Stresses
Beam Design
Subassembly 3
Subassembly 4
Tensile stresses away from the ends of unbonded post-tensioned precast coupling beams remain small as a result of the development of a diagonal compression strut. Transverse mild steel reinforcement is needed at the beam ends where localized critical tensile stresses develop. Longitudinal mild steel reinforcement is used to transfer the angle forces into the beam.
longitudinal
reinforcement
thru ducts for
angle connection
PT duct
transverse
reinf.
confined concrete
Experimental Program
Half-scale pseudo-static reversed cyclic experiments of six coupled wall floor subassemblies will be tested as part of this project. The properties of the first four specimens were determined based on the four subassemblies investigated analytically above. The test specimens are currently being produced by StresCore, Inc. in South Bend, Indiana. Testing is scheduled to begin in April-May 2005.
Conclusions
The results show that the coupling beams have stable behavior through large rotations, significant self-centering capability due to the post-tensioning force, and significant energy dissipation due to the yielding of the top and seat angles at the beam-to-wall connections.
As a result of gap opening, the tensile stresses in the beam and the wall piers remain relatively small even under large nonlinear displacements, thus, significantly reducing the amount of bonded mild steel reinforcement (e.g., transverse shear reinforcement) needed inside the beam.
Acknowledgements
NSF Grant No. NSF/CMS (Dr. P.N. Balaguru)
Precast/Prestressed Concrete Inst. Daniel P. Jenny Fellowship
StresCore, Inc., South Bend, Indiana
Cary Kopczynski of Cary Kopczynski and Company, Inc.
Dywidag Systems International, U.S.A., Inc.
Precision Post Tension, LP, Dallas, Texas
Department of Civil Engineering and Geological Sciences
UNIVERSITY OF NOTRE DAME