An advanced finite element model was presented based on fiber beam-column element.In order to investigate the resistance mechanism of steel frame structure subjected to progressive collapse

non-linear static Pushdown analysis was carried out in two cases.The center column was removed in one case while the boundary column collapsed in the other.Analytical results show that the residual structure has different resistance mechanism in the two cases.In the case of middle column removal

bending resistance and catenary action resistance offer the anti-collapse capability of the residual frame structure

and catenary action effect is developed only in the first and second floor beams in the damaged bay

other beams do not form the catenary action.In the boundary column removed case

only bending resistance provides resistance capacity to the remaining beams

catenary action cannot form in any beams in damaged bay.