Safety assessment of bridge decks under exceptional traffic loads

Exceptional traffic loads, or overweight loads, represent a critical issue for many of the existing reinforced concrete bridges on the Italian motor-way network, as these bridges were designed for different loading conditions to those imposed by today’s overweight convoys. Furthermore, as these structures were mainly built during the twenty-year period between the 1950s and 1970s, deterioration due to chloride-induced corrosion caused by the use of deicing salts is often observed on both piers and deck members. This phenomenon has a significant impact on the structural integrity and load-bearing capacity of the structural elements. Consequently, in-depth structural assessments are required. In Italy, the current standards on these issues are the Italian Design Code (NTC 2018) and the Existing bridges Guidelines 2022 (LG22). In this paper, the structural performance of existing bridge decks under exceptional traffic loads is assessed by applying the principles outlined in NTC 2018 and LG 2022. The results of this assessment are also compared with those obtained from another advanced methodology based on nonlinear static (push-down) analysis, which considers the nonlinear behavior of materials. By using the push-down analysis, the structural behavior under incrementally applied loading steps can be monitored, the activation of inelastic hinges can be detected, and, from the obtained force-displacement capacity curves, the failure load (or failure load factor) can be determined as well. The results obtained using the commonly adopted linear analysis are compared and discussed with those coming from the push-down procedure. This is achieved by applying the two different approaches to various deck configurations.