Probabilistic seismic performance assessment of seismically isolated buildings designed by the procedures of ASCE/SEI 7 and other enhanced criteria

Recent studies have shown that seismically isolated buildings designed by the minimum criteria of ASCE/SEI 7 may have unacceptable probabilities of collapse in the MCE_R. Acceptable probabilities of collapse in the MCE_R are achieved when the isolation system displacement capacity and the strength of the superstructure are increased. The same studies have shown that conventional buildings designed by the minimum criteria of ASCE/SEI 7 have acceptable probabilities of collapse in the MCE_R, and that the collapse probabilities may be much lower than those of minimally designed seismically isolated buildings and may even be lower than those of seismically isolated buildings designed by enhanced collapse performance criteria. This paper investigates what isolated buildings offer in terms of performance criteria other than collapse performance. Based on a probabilistic approach, mean annual frequencies of exceedance of story drift, residual story drift and floor acceleration are computed for a number of isolated and non-isolated buildings that meet the minimum criteria of ASCE/SEI 7 and other enhanced criteria. Based on the mean annual frequencies, probabilities of exceeding response limits that relate to damage are computed for a lifetime of 50 years. It is shown that seismically isolated buildings designed by the minimum or enhanced criteria generally have lower probabilities to develop damage or to be in need of demolishing in 50 years of lifetime than any minimally designed non-isolated building.