Numerical Studies on the Creep Behavior of Shear Endplate Connection Assemblies UNDER Transient Heating

Correct assessment of the steel connection performance under fire requires including the time-dependent response of steel material in the structural analysis. Failure to do so might impose critical threats on the stability and integrity of steel structures. To this aim, the objective of this study is to investigate the effect of thermal creep on the behavior of shear endplate beam-column connections subjected to transient-state fire temperatures. First, finite element models of shear endplate assemblies are developed using ABAQUS and validated against experimental work available in the literature. Parametric studies are then carried out to study the effect of key geometrical, thermal, and material parameters on the overall response of the frame assembly in fire while explicitly including creep. This includes heating and cooling rates, initial cooling temperature, column size and height, load ratio, plate thickness, and steel grade. The results show that including thermal creep causes a reduction in the induced compressive forces and an increase in the mid-span beam deflection, for about six times higher in some cases, thus earlier development of beam catenary action. It is also concluded that lower heating and cooling rates result in larger beam tying forces on the shear end plate connections, which can reach values around ten times larger than when creep is neglected. This study shows that the current practice of neglecting creep in fire analyses, especially in slow heating, may underestimate the forces that are exerted on the shear endplate connections during fire and thus leads to unsafe structural design.