Lateral displacement and collapse of single-story steel frames in uncontrolled fires

Abstract

In industrial and commercial single-story steel-framed buildings, the collapse mode and lateral displacement of unprotected frames in large uncontrolled fires affect in part the integrity of firewalls. In this study, the complete deformation sequence of frames, from initial thermal expansion, followed by either column buckling or formation of plastic hinges in the beams, to collapse was used to determine the safe clearance required between the frame and the firewall to allow the frame to expand laterally without contacting and damaging the wall. An experimentally validated nonlinear finite element model, using ABAQUS, was developed to simulate the heat transfer to the frame and its subsequent thermal expansion and collapse. Both geometric and temperature-dependent material nonlinearities and creep were included in the analysis. The collapse mode of single-story bare steel frames depends on the fire scenario and could be toward the firewall when fire is localized close to the wall or in the more desired mode away from the wall. Lateral displacement of frames increases with the increase of spatial extent of fire. The greater the roof weight, the sooner the failure will occur and the smaller is the minimum clearance between frames and firewalls. The importance of including creep in analysis increases with higher roof loads and taller columns. Uncertainties in the steel mechanical properties at high temperatures affect the predicted performance of frames and hence the safety of firewalls.