Nonlinear analysis on mechanical behaviour of high strength steel extended endplate connections and equivalent T-stubs in fire considering axial force

In fire, ignoring the axial force acting on the high strength steel (HSS) beam-column endplate connections when considering catenary action may lead to a safety risk for the whole steel structure. Hence, a nonlinear analysis is conducted to reveal the actual performance of HSS T-stubs and HSS extended endplate connections in fire using the software ABAQUS. The ultimate displacement, failure mode and bearing capacity of HSS T-stubs under tension-shear combined action are investigated. The failure modes and moment–rotation curves of HSS endplate connections obtained by the numerical study are verified with test results in fire. Furthermore, the effects of bolt diameter, endplate thickness, endplate strength, the combination of endplate thickness and endplate strength, as well as temperature on the mechanical behaviour of HSS endplate connections considering axial force are studied. The results of nonlinear analysis are verified against Eurocode 3 Part 1–8 in various situations. The results indicate that when the shear-to-tension ratio is 2.0, the tensile bearing capacity and ultimate displacement of HSS T-stubs at 600 °C decreased to 38% and 31% of the pure tension, respectively. The parametric analysis shows that when the temperature is 600 °C, the initial stiffness and ultimate flexural capacity of connections are only about 40% and 31% of that at 20 °C.