Evaluating post-fire mechanical performance of S355J2W weathering steel with different artificial cooling approaches

Compared with carbon steel, traces of Ni, Cr, Ti, and other corrosion-resistant alloying elements were added to the matrix of bridge weathering steel, which resulted in the steel surface forming a strong adhesion and dense patina that hindered the penetration of atmospheric oxygen elements into the steel and significantly delayed the development and spread of rust corrosion. Therefore, the weathering steel owes its uniqueness to the formation of a patina that protects the steel from further corrosion. The change in its chemical composition partially influences the phase-transformation temperature, which further affects its post-fire performance. As weathering steel without coating is increasingly adopted in bridge construction, investigating its mechanical properties after fire exposure using different cooling methods is important. Therefore, the mechanical properties of S355J2W bridge weathering steel under rising temperatures and subsequent cooling using three approaches such as cooling in air (CIA), foam (CIF), and water (CIW), were investigated experimentally. Tensile experiments on post-fire S355J2W steel specimens with three different artificial cooling methods were performed to obtain the stress-strain relationships. The tensile fracture morphology was studied using Scanning electron microscope (SEM). The effects of the rising temperature and cooling approach on the mechanical performance of S355J2W steel were analyzed. The results indicated the influence of rising temperature and artificial cooling approach is not significant on the elastic modulus of S355J2W steel, but had an effect on the ultimate strength, yield strength, and ductility. Finally, predictive equations were proposed concerning the post-fire performance of S355J2W steel, laying a foundation for assessing the behavior of bridge weathering steel after fire.