Tensile behavior of corroded high-strength steel components after fire under air and foam cooling

Abstract

In engineering practice, many steel structures in service are inevitably corroded, making them more susceptible to severe damage after exposure to fire. Therefore, assessing the post-fire tensile properties of corroded structural steel is crucial. This study conducted tensile tests on Q690 high-strength structural steel components, subjected to varying levels of corrosion, heating temperatures, and cooling methods (air cooling and foam fire extinguishing agent cooling), to examine their stress-strain behavior, reduction coefficient of mechanical properties, failure modes, and surface strain fields under these combined factors. A predictive model incorporating the combined effects of corrosion, exposure temperature, and cooling method was developed to describe the post-fire mechanical properties of the corroded Q690 steel. In addition, a 3D scanner was used to analyze the damaged surface morphology of the tensile components. The obtained corrosion morphology was then imported into the finite element model for numerical analysis using three-dimensional reverse reconstruction technology. According to this study, below 500 °C, corrosion was the main factor influencing the strength. Above 500 °C, temperature became the dominant factor, with strength decreasing rapidly as temperature increased. When the exposure temperature exceeded 700 °C, the influence of cooling methods on the mechanical properties of steel became pronounced. High temperatures also caused the corrosion-induced pits to expand. The damage depth generally followed a normal distribution, and as the pit depth increased, stress triaxiality increased while fracture equivalent plastic strain decreased.