Fragility curves for the seismic vulnerability of a stock of Italian highway bridges

The present study aims to analyze a stock of highway bridges of the Italian motorway network for the determination of analytical fragility curves, based on nonlinear modal pushover analyses. Fragility curves represent a valid and reliable tool for seismic risk evaluation and allow to correlate the probability of damage exceedance to the earthquake intensity, here represented through the peak ground acceleration. Fragility curves are fundamental in bridge management software to evaluate possible intervention scenarios and to schedule maintenance or retrofitting works by optimizing the economic resources. The obtained results showed a recurrent failure sequence: for increasing values of the peak ground acceleration, a shear failure of the pier is detected at first, followed by the bending failure of the base section of the pier and the unseating of the deck. Furthermore, the behavior in the transverse direction of the bridge results more critical, especially for long viaducts. The fragility curves were also compared with the ones presented in the scientific literature by other researchers for different bridge stocks. The curves result in agreement with the ones determined by other researchers with nonlinear static analyses, while they result conservative with respect to those determined with nonlinear time history analyses.