2-D Analysis Of The Performance Of Connections With Unprotected Steel Structural Members Exposed To Parametric Fire (2003)
AuthorsCHANG, JEREMYshow all
This report examines the performance of steel and composite steel beams, frames, and steel trusses subjected to realistic fires. High axial tensile forces at the beam connections are induced while cooling and could cause failure at the beam connections. Two-dimensional structural analysis and the thermal analysis were carried out using the SAFIR finite element program. An unprotected 610UB101 steel section was used for the steel beams; and the composite beams were formed by the unprotected steel beams acting compositely with the reinforced concrete slab and spanning between steel columns which were assumed to be fire protected. The results show that the induced tensile axial forces are larger in the frames without composite action. They also show that the maximum compressive force is larger when the connections have rotation fixation, but the maximum tensile force is independent of the connection type. The report also investigated the effect of changing the stiffness and strength of the columns. The results show that stronger columns induce larger tensile forces while cooling, and the resulting behaviour of the beam is very similar to the single span pinpin connected beam. When comparing fast fire growth and slow fire growth, the axial forces in the steel and composite beams were strongly dependent on the maximum steel temperature reached during the fire, and largely independent of the fire duration. The last section discusses the structural fire behaviour of steel trusses with the same dimensions as in the World Trade Center tower, with and without insulation. The results show excellent behaviour if the insulation remains in place, but rapid failure due to high axial forces if the insulation is removed.