Coupled CFD–FEM Simulation Methodology for Fire-Exposed Bridges

Evaluating the fire performance of bridges is necessary for damage mitigation as more fire-related accidents occurred on bridge structures. Current solutions adopting temperature curves can result in significant inaccuracy by neglecting the inhomogeneous characteristic of the fire-induced thermal environment. This paper proposed a numerical methodology for analyzing the coupled thermomechanical response of various bridges exposed to fires. The computational fluid dynamics (CFD) approach was implemented to reproduce the fire condition more realistically by modeling the combustion process and fire-driven flow. Then, an interface was adopted to extract the thermal boundary from the fire model. At last, the thermomechanical finite-element method (FEM) was coupled with the CFD model for determining the fire-induced response of the global bridge, thermally and structurally. By incorporating the multiscale FEM, this methodology can be extended to various large-scale bridges subjected to localized fires. The proposed approach was validated through a real fire experimental study on a steel column. To demonstrate the application of this strategy, a complex case study was carried out. A long-span cable-stayed bridge was investigated considering its girder segment was exposed to an under-deck tanker fire. Numerical results showed that the proposed method was able to capture the surrounding temperature field with strong thermal gradients and can predict not only the localized thermomechanical response of exposed segments but also the global structural performance evolution for large-scale complex bridges. The under-deck fire can introduce a significant impact on the entire cable-stayed bridge. Thereby, the multiscale FEM modeling strategy is required for the long-span bridges exposed to localized fires.