Seismic fragility of non-ductile RC frames for pounding risk assessment

Building structures subjected to seismic excitation tend to vibrate with a unique set of dynamic characteristics, such as natural frequencies, fundamental mode shapes etc. In series-configured structural systems, a difference in such characteristics induces a phase difference between the structures' oscillations, leading to structural collisions or pounding. Pounding often becomes a cause of catastrophic failures, hence an accurate estimation of structural integrity with respect to pounding is of paramount importance. This study aims to examine different fragility curve development methodologies available in the literature to assess the seismic performance of adjacent Reinforced Concrete (RC) structures subjected to structural pounding. The study primarily focuses on displacement-based fragility curves for the highly critical floor-to-column interactions of an eight-storey non-ductile RC frame, non-eccentrically adjacent to a three-storey rigid RC frame having different storey heights. Nonlinear time-history analyses have been performed to simulate pounding, and fragility curves have been generated using five methodologies. The direct Monte-Carlo Simulation technique has been used to benchmark against the obtained results to identify the suitability of each fragility assessment technique. Results indicate that even though there is no effect of the choice of assessment methodology on the estimated risk at low performance levels and intensity measures, the disparity becomes clearly visible at higher levels. The study presents alternate ways of developing accurate fragility curves by keeping in mind the need for computational efficiency without compromising the accuracy of results. The High Dimensional Model Representation meta-model is found to efficiently represent target pounding fragilities while incurring minimal computational costs.