Experimental and numerical investigation on mechanical behavior of Q355 steel and connections in fire conditions br

Understanding the temperature-dependent mechanical behavior of steel materials is the basis for evaluating collapse resistance of a steel structure and assessing its after-fire safety. Tensile experiments are conducted on Q355 steel to study the influence of heating histories and stress triaxialities on mechanical behavior in the whole process of fire including heating, heating-cooling and after-fire stages. The true stress-strain curves are measured, and microscopic failure mechanism is investigated. A SMCS model is used to simulate fracture behavior of steel and the model parameters are calibrated based on experimental and numerical results. A parametric study is conducted to study mechanical performance of steel connections under and after fire. The experimental results show that Q355 steel exhibits ductile fracture behavior under and after fire. The higher the tensile and peak temperatures, the greater the fracture strain and the better the ductility. The stress triaxiality may affect the sensitivity of fracture behavior of steel to the temperature condition. The SMCS model is applicable to evaluating fracture performance of Q355 steel in fire, with errors less than 10%. The fracture model of steel materials has a great influence on the mechanical performance of connections in fire. The ductility coefficient of steel connec-tions in fire can be increased to 1.8 times the ambient-temperature value.