Collapse in sliding isolated MRFs considering different design methodologies

Seismic isolation protects both the structural and non-structural component at the expense of large horizontal displacement at the isolation level. Under some circumstances the excessive displacement may exceed the displacement capacity of sliding isolation bearing or cause the impact against the retaining wall, both of which may damage or even precipitate collapse of the superstructure. In this study a comprehensive numerical model, capable of capturing bearing uplift failure and nonlinear superstructure behavior, is used to investigate the effects of superstructure yielding on the collapse performance. Previous studies have not explicitly included bearing failure. Three base-isolated systems are designed; one designed to the ASCE 7 code, one with increased superstructure strength, and one with increased bearing displacement capacity. Fourteen pairs of near-fault pulse-like ground motions are used for the collapse risk assessment. Following the FEMA P695 methodology, the collapse margin ratio, system-level collapse mechanism and probability of collapse are quantified. Analysis results show that increasing bearing displacement capacity is more effective at minimizing collapse probability; however, this results in minimal margin between bearing rim impact and collapse. Additionally, the modes of collapse for each design are compared.