Simplified Prediction of the Thermal and Mechanical Behavior of a Cold-Formed Steel Composite Floor at Room and Elevated Temperatures

Abstract

This paper presents a simplified method to predict the thermal and mechanical behavior of a new cold-formed steel floor system at room and elevated temperatures. A four-point bending test of such a floor assembly was performed at room temperature, and an efficient method to estimate the elastic rigidity and strength of the floor system was verified. The temperature progression of the floor section in a fire situation was well predicted based on the implicit finite difference method, taking into account the effects of ceiling materials falling off. A thermal-mechanical model was then developed by simplifying the floor system to a laterally restrained joist subject to constant vertical load and a non-uniform temperature distribution. The time-dependent vertical deflection of the floor joist was well predicted, whereas the response in the final stage of fire exposure was overestimated, probably due to the severe joist degradation and the neglected contribution of the autoclaved lightweight concrete subfloor. In addition, the fire-resistance time estimated by the simplified formula was found to compare well with the previous experimental results.