Comparison of Seismic Design Methods for Irregular RC Bridges

In this paper, the non-linear seismic response of an irregular 457m reinforced concrete (RC) box-girder bridge is examined in detail. The bridge was originally designed based on the current prevailing international design capacity philosophy, in which bridge strength and ductility capacities are designed to meet strength and ductility demands, as found from a response spectrum analysis. To determine the appropriateness of this design approach, a non-linear time-history analysis methodology is devised for the bridge. As part of this methodology, synthetic accelerograms are created, based on a site-specific response-spectrum, and used in non-linear time-history analyses of the bridge, in which ductile elements have been modelled using bi-linear hysteresis models. The results obtained from the linear and non-linear analyses are compared and significant deviations in load effects and ductility demands are found at key locations along the bridge. The significance of these deviations is discussed. Additionally, seismic performance enhancing bridge design alterations are also suggested.