Seismic Response of Simply Supported Base-Isolated Bridge with Different Isolators

The seismic response of simply supported base-isolated bridge with different isolators is presented. The isolated bridge deck is idealized using simplified model of a simply supported rigid deck with three degrees-of-freedom, two lateral translational, mutually orthogonal and one rotational. The rotational degree-of-freedom of the bridge deck may arise because of the dissimilarity in properties of different seismic isolation devices such as elastomeric and sliding systems supporting the bridge deck. The sources of dissimilarity in the isolators considered here are the isolation stiffness and the yield force. The flexibility of abutments and bridge deck is ignored and two horizontal components of earthquake ground motion are applied, considering bi-directional interaction of the seismic response. The governing equations of motion for the uncoupled and torsionally coupled bridge are derived and solved using Newmark’s method of integration to obtain the seismic response. The parametric studies are conducted for different system configurations, isolation systems and frequency ratios during torsionally coupled and uncoupled conditions. The seismic response of base-isolated bridge is seen to be considerably altered due to the dissimilarity in the isolator properties. The eccentricity arose due to the isolation stiffness affects more than that due to the isolator yield forces. The effectiveness of isolation reduces athigher eccentricities and the torsionally coupled response diminishes with the increase of uncoupled torsional to lateral frequency ratio.