Seismic Risk Assessment of a 42-Story Reinforced Concrete Dual-System Building Considering Mainshock and Aftershock Hazard

Abstract

A seismic risk assessment of a 42-story reinforced concrete dual-system building considering mainshock and aftershock hazard is presented. Sequential nonlinear response history analyses are performed using as-recorded mainshock-aftershock sequences. Aftershock assessment describes the case where the mainshock has occurred, and the associated damaged state of the building is known. A Markov process model is used to integrate the increase in vulnerability of the mainshock-damaged building with the time-dependent aftershock hazard. Aftershock risk is quantified as the probability of exceeding the structural response demand limits used in performance-based seismic design of tall buildings at different instants in time following the mainshock. The same metric is used to quantify mainshock-aftershock risk; however, for this type of assessment, the uncertainty in the intensity and damage caused by both the mainshock and aftershock is considered. The results of mainshock-only, aftershock, and mainshock-aftershock assessment show that the coupling beam rotation demand limit generally has the highest probability of exceedance compared with the peak transient and residual story drift ratios, frame beam rotations, and compressive and tensile strain in boundary element concrete and steel, respectively. The implied 50-year exceedance probabilities of the demand limits currently used for the collapse prevention performance level were found to vary significantly across the various response parameters.