Probabilistic seismic demand model for curved reinforced concrete bridges

This article examines the seismic behaviour of curved box-girder concrete highway overpass bridges commonly built in California. In particular, a probabilistic seismic demand model for curved 5-span reinforced concrete box-girder bridges with single circular column bents is developed. The principal parameter of the demand model is the bridge curve radius in the horizontal plane, varying from infinity (representing a straight bridge) to a sharp curve radius equal to the length of the bridge. Three bridge prototypes are analyzed: (1) a tall-column bridge with relatively low lateral stiffness; (2) a bridge commonly designed in California and (3) a short-column bridge with high lateral stiffness. A probabilistic seismic demand analysis, including a modal analysis and an evaluation of the nonlinear static and dynamic response, are performed for each bridge prototype and each radius value. The magnitude-distance bin approach is used to cover a range of plausible ground motion scenarios. The probabilistic demand models are cast in terms of one engineering demand parameter, the bridge drift ratio, and two intensity measures: the peak ground displacement or velocity, and the spectral displacement at the fundamental period of the bridge, S-d (T-1). The demand models show an increase in transverse-direction drift ratio demand for sharply curved bridges.