EXPERIMENTAL INVESTIGATION OF CONCRETE COUPLED WALL SYSTEMS WITH POST-TENSIONED STEEL COUPLING BEAM

Post-tensioned coupled shear wall system is characterized by good seismic specifications like a self-centering capability and an ability to sustain large nonlinear lateral deformations with little damage and negligible residual deformation. In this system, the coupling beam is not embedded into the walls, and coupling of concrete walls is performed by posttensioning beam to the walls using unbonded post-tensioning (PT) steel strands. In this paper, the seismic behavior of hybrid coupled wall systems with post-tensioned steel coupling beam was investigated experimentally. In order to dissipate seismic energy and reduce displacements of system, two friction dampers were used in the beam-to-wall connection region. To study the behavior of the system, a friction damper was first tested at different frequencies; then, four 2/3-scale posttensioned hybrid coupled wall sub-assemblages equipped with friction dampers were tested subjected to reversed-cyclic lateral loading. Each sub-assemblage included a half-length steel coupling beam and the adjacent concrete wall region at a floor level. The test specimens consisted of one control specimen without friction damper and three specimens equipped with friction dampers with various damper normal forces and different initial beam post-tensioning (PT) steel stresses. The test results showed that the system had very good lateral stiffness, strength, and ductility with little damage up to 8% lateral drift. The nonlinear deformation in this system occurs because of the gap opening at the beam-to-wall interface. The friction damper uses these gap opening displacements to provide supplemental energy dissipation. Friction dampers provide considerable energy dissipation at the system, while the self-centering capability of the system remains. The restoring effect of the post-tensioning steel strands causes closing the gap upon unloading and provides a self-centering behavior and flag-shaped hysteresis loops for specimens equipped with friction dampers. Based on the test results, the system, even after a severe earthquake, suffers limited damage and requires little repair.