Seismic Risk Assessment of Highway Bridges

In this paper a numerical procedure for the evaluation of seismic risk and vulnerability of highway bridges is described. First, the pushover curve of each structural subsystem (i.e. pier/abutment + bearing/isolation devices) is determined. The contributions of the subsystems are then properly assembled to provide the Capacity Curve of the entire bridge, both in the longitudinal and transverse direction. The Capacity Curve is then step-bystep converted into an equivalent SDOF Adaptive Capacity Curve and intersected with the Demand Curve, represented by an over-damped normalised response spectrum, to provide the PGAs associated to specified damage states for piers and bearing/isolation devices. Based on the PGA values thus obtained, fragility curves (seismic vulnerability) and annual probabilities of exceedance (seismic risk), for a bridge located in a given site, are obtained. The method also gives the possibility to consider possible modifications of strength and ductility, due to decay of materials and/or rehabilitation interventions and/or seismic retrofit interventions.