STATE-DEPENDENT VULNERABILITY OF CASE-STUDY REINFORCED CONCRETE FRAMES

This study investigates the effect of mainshock-aftershock sequences on numerical fragility and vulnerability relationships of European reinforced concrete (RC) moment-resisting frames (MRFs). A four-story, four-bay nonductile RC MRF is selected for illustrative purposes. This index building is representative of a typical vulnerability class in the Mediterranean region. The influence of the masonry infills on seismic performance is also investigated. An advanced numerical nonlinear model is developed for the case-study frame and then assessed through nonlinear dynamic analysis using both real and artificial mainshock-aftershock sequences, via a ‘sequential cloud’ approach. The obtained seismic demand estimates allow to generate fragility functions for the undamaged frame when subjected to mainshocks only. Moreover, statedependent fragility functions are derived for the mainshock-damaged frame when subsequently subjected to aftershocks. Damage-to-loss models, specifically calibrated on Italian post-earthquake data, are used to derive vulnerability functions for this case-study structure. Preliminary results from the study show that the frame experiences severe damages states and high losses for a range of ground-motion shaking intensities, with a clear damage increase due to aftershocks. An attempt to generate vector-valued mainshock-aftershock vulnerability relationships is finally presented. The proposed vulnerability surfaces can be more easily implemented into a time-dependent risk assessment framework.