Unbonded Post-Tensioned Precast Concrete Coupling Beams:An Experimental Evaluation

摘要

This paper describes the observed nonlinear reversed cyclic behavior of a half-scale precast concrete coupling beam subassembly for seismic regions. In this new system, coupling of concrete walls is achieved using unbonded post-tensioning. The test specimen includes a coupling beam and the adjacent concrete wall regions at a floor level. Under lateral loads, the nonlinear deformations of the coupling beam occur primarily due to the opening of gaps at the beam-to-wall interfaces. Steel top and seat angles are used at the beam ends to yield and provide energy dissipation. Prior to the testing of the specimen, the concrete at one end of the beam had to be patched due to poor consolidation during casting. The beam was able to sustain three cycles of displacement at 6.4% chord rotation and failed during the second cycle to 8% rotation due to the low cycle fatigue fracture of one of the top and seat angles. Most of the damage in the beam was concentrated in the angles (which can be replaced after an earthquake) and the patched concrete. The unpatched end of the beam received almost no damage other than a small amount of cover concrete crushing at the corners. The mild steel reinforcement in the beam performed well throughout the entire displacement history; however, premature fractures of post-tensioning strand wires occurred inside the anchors.