Understanding of the performance of critical bridges, such as cable-supported bridges, during accidental fire is necessary for developing mitigation strategies against potential fire damage. In this research, the structure-fire interaction of long-span cable-supported bridges, in particular, anchored suspension bridges, self-anchored suspension bridges, and cable-stayed bridges, was investigated through nonlinear finite-element analysis. To investigate the stability of these bridges during fire, a typical steel orthotropic box girder was exposed to different fire scenarios representing fires during ship and truck accidents. The stability of the three bridges during two fire scenarios was investigated in terms of fire intensity and duration and axial compressive force in the deck. Simulation results indicate that the existing axial force in the deck negatively affected the structural performance by causing buckling failure under fire loads. Generally, anchored suspension bridges had the largest safety factor among the three bridges because of nearly zero axial force in the deck. On the other hand, self-anchored suspension bridges had a significantly higher amount of existing axial compressive force in the deck and were the most vulnerable during both the truck and the ship fire scenarios. The axial forces in cable-stayed bridge decks varied longitudinally. Hence, their vulnerability during fires depends on the location of fire, the magnitude of existing axial force, and the design capacity of the deck.

According to Federal Highway Administration, impact by moving trucks is the 3rd leading cause of bridge failure or collapse in the country. Although current AASHTO LRFD Guide Specifications prescribe designing bridge piers by applying a 400 kips static load at a height of 4ft to improve their impact resistance, recent studies have shown that the dynamic forces because of truck impacts may be significantly higher than that recommended by the AASHTO Guide Specifications. In this paper, we present an extensive investigation on the impact of a three-span steel girder bridge with reinforced concrete piers by trucks running at different speeds through models of bridge and the truck in LS-DYNA, including a correlation between seismic and impact resistance of bridge piers. Results also present a comparison between static load prescribed by AASHTO Guide Specifications and dynamic impacts loads observed during numerical simulations. A performance based approach is proposed to design bridge piers against truck impacts.