Experimental Evaluation of Unbonded Post-Tensioned Hybrid Coupled Wall Subassembalges

This thesis describes an experimental research program on the nonlinear behavior of coupling beam subassemblages in a new type of hybrid coupled wall system for seismic regions. Coupling of concrete walls is achieved by post-tensioning steel beams to the walls using unbonded post-tensioning strands. Different from conventional hybrid coupled wall systems, the coupling beams of the new system are not embedded into the walls. Tests of three half-scale coupled wall subassemblages were conducted under pseudo-static reversed-cyclic loading. Each subassemblage included a steel coupling beam and the adjacent concrete wall regions at a floor level. Top and seat angles were used at the beam-to-wall connections of one of the test specimens to yield and provide energy dissipation to the structure. The experimental results show that unbonded post-tensioned steel coupling beams can provide significant and stable levels of coupling without experiencing significant damage over large nonlinear cyclic deformations. The nonlinear deformations of a properly designed coupled wall subassemblage occur primarily as a result of the opening of gaps at the beam-to-wall interfaces. The post-tensioning force provides a restoring effect that closes the gaps and pulls the structure back towards its undisplaced position upon unloading from a large nonlinear deformation. This results in a large self-centering capability of the system. The behavior of unbonded post-tensioned steel coupling beams without top and seat angles at the ends is close to a nonlinear-elastic type of behavior with little energy dissipation. Yielding of the top and seat angles as a result of gap opening at the beam-to-wall interfaces provides a considerable amount of energy dissipation the structure. The angles are considered as sacrificial components that would need to be replaced after a large earthquake. It is concluded that unbonded post-tensioned steel beams offer an effective and feasible means to couple reinforced concrete walls in seismic regions.