Seismic Performance of Multi-Span RC Railway Bridges

Presently, there is no clear method for determining the optimal railway bridge design for a particular ground type and expected seismic intensity. Four main types of RC bridge dominate the current multi-span railway bridge design trends – the Simply Supported Beam, Continuous Box-Girder (CBG), CBG with Lead Rubber Bearing (LRB) supports and the laterally fixed continuous deck (CRB) with LRBs. In this paper, the seismic performance of these four types is examined for varying ground types and seismic intensities. For the purposes of comparison, all of the bridges have five spans with identical span lengths and topography. Initially, typical bridge deck, pier and bearing configurations are chosen and analyzed through a series of nonlinear time-history analyses using synthetic accelerograms, in which plastic hinge formation is permitted. Next, an optimization of the bridge configurations is undertaken to increase the performance and reduce the overall bridge cost. Finally, an evaluation of the lifetime bridge costs are made assuming current prices, including costs relating to the damage associated with the expected seismic events. This is accomplished through the use of approximated damage states and fragility curves in relation to PGA. The cost comparisons clearly show that particular bridge types perform better than others economically for specific ground types and expected seismic intensities, even though in some cases they may be expected to suffer larger damages during their lifetime.