Nonlinear dynamic behaviour and seismic fragility analysis of irregular multi-span RC bridges

This paper investigates the nonlinear dynamic behaviour and failure probability of multi-span Reinforced Concrete (RC) bridges supported on piers of unequal heights. To this end, a three-dimensional nonlinear finite element model of RC bridges with substructure irregularity is developed. The model is verified against an available experimental data of a large-scale shake table test results of a benchmark irregular two-span RC bridge. Six hypothetical two-span irregular RC bridges with piers varied in height, and various superstructure mass-distribution conditions (equal and unequal) and a regular bridge layout (as a reference) are considered. Through Incremental Dynamic Analyses (IDAs), the seismic performance of selected bridge layouts is investigated at both local and global scales. Finally, the influence of bridge layout on seismic vulnerability of piers of varying heights is analysed. Results show that the unbalanced seismic displacement demand and failure probability of different bents of a multi-span irregular RC bridge significantly depend on the height of piers and their arrangement. Therefore, the typical presumption of shorter piers having a higher failure probability due to their higher seismic force absorption is not always the most possible failure mechanism.