Collapse performances of steel frames against fire considering effect of infill walls

This study numerically investigates effect of infill walls on collapse performances of three-dimensional (3D) steel frames against fire using explicit nonlinear dynamic analysis. Two eight-story, five-span with three-bay composite steel frames were designed, one of which has no infill walls (bare frame) while the other one has infill walls (infilled frame). The fire resistance, load redistribution mechanisms of the structures subjected to single compartment fire are investigated. Frame analysis against traveling fires is also conducted. Moreover, the effect of parameters including load ratio, opening percentage and number of infill walls are also studied. Results indicate that the damaged compartment moves down in fire and drags the other part of the frame, causing overturning deformation in the frame in the short span and the twist of the entire structure. The infill walls decrease the buckling temperature of the heated columns, whereas significantly increase the collapse temperature of the steel frames. The strut action of infill walls drastically changes internal forces within adjacent columns, significantly altering load redistribution path of steel frames against fire. The collapse modes of the steel frames can be greatly altered by the presences of infill walls. The steel frames collapse at a lower temperature with increasing load ratio and opening percentage of infill walls, whereas collapse at a higher temperature with more infill walls. Finally, a preliminary analytical approach is proposed to predict collapse modes of steel frames against traveling fire.