Residual Strength of Steel Structures After Fire Events Considering Material Damages

It is an essential task for engineers to evaluate the residual strength of a fire-damaged steel structure, especially when collapse does not occur during the fire event. First of all, the mechanical properties of structural steels after fire were investigated through the experimental data. The stress-strain relationship model considering fire events was established. Then, the remaining load bearing capacity of a simple steel frame was evaluated using both the fiber and shell element numerical models. Finally, case study about the post-fire residual strength of a complex steel truss bridge was carried out. The results show that mechanical properties of the structural steels decrease after cooling down from an elevated temperature higher than 500 degrees C. Compared with the shell element model, the fiber element model is not able to predict accurately the post-fire inelastic behavior of a thin-walled steel structure. In most cases, the fire-exposed steel bridge still retains its original strength. However, it is apparently affected by the positions where the fire breaks out. The worst-case scenario is that the fire event occurs at the joint near the bearing supports, in which the strength decreases dramatically.