Change in response of bridges isolated with LRBs due to lead core heating

This study focuses on the response of seismic isolated bridges subjected to near-field ground motions with distinct pulse type behavior in terms of maximum isolator displacements (MIDs) and maximum isolator forces (MIFs) transferred to the substructure. The employed isolation systems are composed of lead rubber bearings (LRBs) with bi-linear force-deformation relations that consider cycle-to-cycle deterioration in the yield strength of the LRBs due to heating of the lead core. MIDs and MIFs with due consideration of cycle-to-cycle deterioration are compared with that of non-deteriorating ones. Bounding analyses are also performed for comparison purposes. Nonlinear response history analyses are conducted with two bins of ground motions recorded at different soil conditions to investigate the effect of ground motion characteristics. Results indicate that MIDs are overestimated by lower bound analyses when seismic isolated bridges are subjected to near-field motions with high velocity pulses especially for the bearings with higher Q/W ratios.