Lifetime seismic performance of concrete bridges exposed to corrosion

This paper presents a probabilistic approach to predict the lifetime seismic performance of concrete bridges exposed to aggressive environments. The time-variant behaviour of critical cross-sections, such as those at the base of the bridge piers, is evaluated in terms of bending moment versus curvature relationships, accounting for the degradation of both concrete and steel. The randomness involved in the diffusion process of the aggressive agents, as well as the material and geometrical uncertainties related to the structural system, is taken into account in probabilistic terms. The assessment of the lifetime seismic bridge performance is therefore obtained by means of probabilistic time-variant nonlinear static analyses of the structural system. The proposed procedure is applied to a four-span continuous bridge with box cross-section piers exposed to corrosion. The results highlight that both strength and ductility of the structural members vary over time, affecting the seismic capacity of the bridge system and eventually causing a shift to an undesirable mechanism of collapse. The results are validated by means of time-history nonlinear dynamic analyses, which confirm the importance of a proper combination of seismic and environmental hazards in the evaluation of the lifetime seismic performance of bridge structures.