Fragility Assessment of RC Bridges Exposed to Seismic Loads and Corrosion over Time

A methodology to estimate the structural fragility of RC bridges, considering the effects of seismic loadings and corrosion over time, is presented. Two scenarios are considered: (a) The structure is exposed only to seismic loads, (b) Both the effect of corrosion and seismic loads are present in the system. The uncertainties related to material properties, structural geometry, seismic occurrences, corrosion initiation time, cracking and corrosion evolution are considered. Different time stages, such as 0, 50, 75, 100, and 125 years are selected to evaluate the effect of both seismic loads and seismic loads plus corrosion. The calculation of fragility curves implies a structural design, nonlinear modeling of structures with simulated properties, estimation of both corrosion times and seismic occurrences, and evaluation of structural demand over time considering the effect of seismic loads and corrosion. An illustrative example is provided on an RC continuous bridge with AASHTO beams, cap beams and circular columns located in Acapulco, Guerrero, Mexico. A performance level equal to 0.002 is chosen for the design of the structure. Results show that the probability of exceeding the design performance levels for both cases (seismic and seismic plus corrosion) are similar at the stage of time equal to zero (a newly built bridge). However, such probabilities, after 150 years, are equal to 0.61 and 0.85 due to the cumulative damage caused by seismic and seismic plus corrosion, respectively. The estimation of the probability of exceeding a certain performance level, considering the effect of corrosion together with seismic loads, highlights the importance of considering more than one type of solicitation for these kinds of structural systems. Lastly, recommendations about design are given.