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 04-09114 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 04-09114 (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 www.nd.edu/~concrete