Influence of fire scenarios on progressive collapse mechanisms of steel framed structures

OpenSees is an open-source object-oriented software framework developed at UC Berkeley. The OpenSees framework has been recently extended to deal with structural behaviour under fire conditions. This paper presents the results of a numerical study, using OpenSees, of the progressive collapse of steel frames exposed to fire. After validating the capability of OpenSees against available analytical and experimental results of fire tests on steel members, a parametric study is carried out to find the progressive collapse mechanism of steel frames exposed to fire and corresponding influencing factors. The factors include load levels, lateral restraint, beam strength and fire scenarios. The catenary action of beams is considered by using a temperature-dependent corotational beam/column element. The results show that different progressive collapse mechanisms can happen due to the sequence of the buckling of columns. High load levels lead to the downward collapse of the whole structure compared with the lateral collapse for low load levels. The existing of lateral restraint causes the premature buckling of bottom columns which triggers the whole frame collapse. As the beam section increases, the collapse mechanism of steel frames changes from beam failure mode to column failure mode. The fire scenarios have significant effect on the collapse mode of steel frames. The work presented in this paper is a preliminary study of the progressive collapse of steel frames. Further work is underway to combine the influence of the effect of concrete floors. A simple design method is then expected to be proposed to investigate the robustness of steel structures against progressive collapse due to fire.