Numerical investigation of a steel tied arch bridge under fire loading

Bridges are strategic infrastructures designed to withstand operating and accidental load conditions. However, among accidental actions, the current structural standards of bridges do not explicitly consider fire actions. However, the fire risk is not negligible, as highlighted by the scientific literature. In fact, despite the probability of occurrence of a fire impacting a bridge is certainly lower than for building, the consequences can be high. Indeed, high vulnerability to the fire of bridges can have a significant impact on the functionality of the infrastructural network. Too high deformations can cause the loss of functionality of the structure with severe repercussions on vehicular traffic and services often incorporated into the structure. The present work fits into this context by analysing the fire vulnerability of a steel tied arch bridge. In most cases, the restraints at the end of the bridge are considered free or fixed‐end conditions. However, the presence of the thermal joints induces restraint conditions that are in between the two limit cases. The modelling of the thermal expansion joints of the bridge was considered. Different plausible fire scenarios were taken into account and were modelled according to natural fire curves. A series of thermomechanical analyses were then developed to identify the failure modes and times of collapse, as well as the deformation behaviour that can cause the loss of functionality.