The effect of fire conditions on behaviors of steel framed structure

In order to study fire response of steel framed structure and the effect of fire conditions on it, load capability and deformation of the structure were analyzed using elastic-plastic theory and fire behaviors of one-story steel framed structure were investigated by non-linear finite element method. The results acquired from numerical simulation are good correlative with ones of experiment. Based on this model, the effect of fire parameters on structure behaviors was discussed using natural fire BFD curve by parametric method. The curves of temperature and gradient, and deflection of the structure are obtained. The results show that temperature rise, fire resistant duration and fire behaviors of the structure are determined by process of fire rise and descent. At the same maximum temperature T_m of fire, if the time t_m at which T_m occurs is long, both rise and descent rates of fire temperature are small, fire duration long. The structure, which has high temperature and large deformation, is liable to failure. When the shape constant s_c of BFD curve is large, fire temperature rises rapidly but descends slowly. The structure is in high temperature for a long time and has large deformation even leads to catenary\´s action. The failure is fast and fire resistant duration short. Those are disadvantage to fire resistance. Compared to "long-cool" model, T_m of "short-hot" model is higher, both rise and descent rates of fire temperature are larger. The structure is in high temperature for a short time and has lower temperature and smaller deformation, which are beneficial to fire resistance. The fire resistant duration is longer, residual deformation is smaller after temperature descends.