Effect of base isolation on the seismic response of multi-column bridges

A nonlinear model for time-step analysis of bridges subjected to two orthog onal horizontal components of earthquake motions was developed. The focus o f the study was on elastomeric isolators with or without lead cores. The hy steretic behavior of the isolators, the columns, abutments, and shear keys was taken into account. The nonlinear analysis showed that, contrary to lin ear theory prediction, the use of isolators does not necessarily increase t he displacement of the superstructure. Furthermore, it was shown that prope rly designed isolators can reduce the ductility demand in RC bridge columns substantially.