Time-Dependent Response of Flush Endplate Connections to Fire Temperatures

This paper summarizes results of a comprehensive computational study on the time-dependent or creep behavior of flush endplate beam-column connections subjected to elevated temperatures due to fire. Using a connection prototype that was previously studied experimentally, creep connection tests were simulated in a finite-element software package to establish the response of flush endplate connections as a function of time. The effect of important design parameters such as shear-to-axial load ratio, endplate thickness, and bolt size on the time-dependent response of flush endplate connections was also investigated in creep connection simulations. Results of creep connection simulations were further used to develop a methodology to quantify the effect of thermal creep of structural steel on the behavior of flush endplate connections in fire. In this methodology, time effects on the strength and rotational capacity of flush endplate connections are explicitly presented in the form of isochronous force-rotation curves. Results from this study clearly indicate that the strength and deformation capacity of flush endplate connections are highly time dependent for temperatures, stresses, and time durations expected in building fires and that ignoring the effect of thermal creep of steel may lead to unsafe predictions of the response of steel connections exposed to fire temperatures.