Finite element modeling of time delay effect on behaviour of CFST columns under nonuniform fire

Most of the past studies about fire resistance of CFST column have dealt with the behavior of this column against uniform fires, while in truth interior columns of the building are actually placed within the walls; therefore, the columns subjected to non-uniform fire which causes the column surfaces exposed to fire with delay. It's important to investigate the effect of fire exposure's time delay on varied column surfaces. In this study, a numerical model was developed to investigate the effect of time delay on fire resistance, residual resistance, and heat distribution of CFST column's cross section. Results show that as the time delay has increased, the samples' fire resistance duration rises too. It also demonstrates that as the number of the sides, exposed to fire becomes more, the impact of time delay on fire resistance as well as the residual resistance of the column drops. Additionally, it has been observed that the ratio of fire resistance in the column, exposed to non-uniform fire with a time delay, to the column under a comprehensive fire is directly related to the reverse ratio of column sides, exposed to fire, to all column sides.