Seismic performance of concrete coupling beams subjected to prior nonlinear wind demands

The ability to assess the role of pre-existing damage on the residual (reserve) capacity and reparability of buildings following a damaging event or events is essential to achieving the goal of functional recovery. If performance-based wind design is applied, where limited nonlinear deformations in some elements are allowed under extreme wind events, or if a design earthquake occurs, there are likely to be a significant number of buildings with modest damage (in addition to some with more severe damage, that obviously need to be evaluated and repaired). For tall concrete buildings that utilize structural coupled (core) walls as the primary lateral force -resisting system, coupling beams are the main fuses that limit force demands on other elements and actions and provide a reliable mechanism for energy dissipation during extreme events, and thus, are most likely to impact building performance in future events and to require repair. Therefore, tests were conducted on eight coupling beams, seven reinforced concrete (RC) beams and one W-shaped steel-reinforced concrete (SRC) beam, subjected to simulated windstorm loading protocols that introduced modest nonlinear deformations followed by a standard seismic loading protocol to large inelastic deformations. The test variables included aspect ratio, presence of an RC floor slab, type of wind loading protocol, level of detailing, and type of concrete coupling beam (RC vs SRC). The findings indicated that the limited damage due to the prior wind demands did not impact strength, axial growth, rotation capacity, and failure mode of the beams under the seismic loading protocol; however, a significant reduction in the initial stiffness of all beams and a minor reduction in energy dissipation capacity of the conventionally reinforced beams were observed.