Vector Form Intrinsic Finite Element analysis of nonlinear behavior of steel structures exposed to fire

This study adopted the Vector Form Intrinsic Finite Element (VFIFE) method to study the nonlinear fire response of steel structures. The numerical model is first verified by comparing the results with the published experimental and analytical results for steel structures. The nonlinear behavior of the fire response of the Williams toggle frame, and the steel frames subjected to earthquake load and fire load are then fully studied. The numerical results show that the bearing capacity of the Williams toggle frame rises markedly with the increase in temperature when the temperature is less than the critical value. However, when the temperature is more than the critical value, the bearing capacity of the Williams toggle frame decreases with the increase in temperature, but its bearing capacity at 1000 ∘C is still larger than the elastic buckling strength at room temperature. In addition, the shallow arch deflects upward before buckling with increasing temperature, and its deflection is much smaller than that of the beam structure with the same span. The structure deflects downward after buckling and shows catenary action when it is re-balanced. In the case of fire induced by an earthquake, the deformation of the structure is significantly affected by the aftershock, fire, and fracture of structural elements.