A methodology for the risk-based design of bridges in Italy

Seismic design codes used worldwide are mainly based on a force-based seismic design approach, employing Uniform-Hazard Spectra (UHS) to select the seismic action and behaviour factors to account for the inelastic behaviour of structures. Lately, following the increasing interest in performance-based earthquake engineering, many studies investigated the reliability of this design approach by assessing the level of structural safety against earthquake actions implicitly achievable following design codes. It emerged that current code provisions do not ensure a uniform level of structural safety. For the abovementioned reasons, the present contribution assesses the seismic structural safety of newly-designed bridges in Italy. In particular, the study proposes a methodology for the risk-targeted design of reinforced concrete piers in multi-span bridges. Such an approach consists in computing the probability of failure of the structure by solving a direct reliability problem, associated with the exceedance of tolerable thresholds of loss. The methodology is applied in various locations across Italy to illustrate the variations in the optimal risk-based design properties of bridges across regions with varying seismic hazard.