Evaluation the effect of middle column removal on the occurrence potential of progressive collapse in reinforced concrete moment frames using sensitivity analysis

In this research, the progressive collapse of the reinforced concrete frames following the middle column removal has been investigated based on the sensitivity and robustness indexes. At first, the numerical model of the reinforced concrete frame was simulated and verified with Li et al. model in SeismoStruct software. After developing the numerical model, the performance levels and the number of plastic hinges in the frames were obtained. The frames were subjected to the column removal in the first story and their vulnerability to progressive collapse was investigated under nonlinear static push down analysis. In the present research, parametric study including change in the number of stories, span length, story height, concrete compressive strength, rebar yield strength, poisson's ratio and damping ratio of the structure in the progressive collapse of the frames was performed based on the sensitivity and robustness indexes. The results showed that increasing the number of stories from 5 to 20 story, reducing the span length from 5.5 to 3 m, reducing the story height from 4.45 to 3.20 m, increasing the concrete compressive strength from 21.3 to 51.3 MPa, increasing the rebar yield strength from 234 to 350 MPa, increasing the Poisson's ratio from 0.12% to 0.25% and increasing the damping ratio from 5% to 15% decreases and increases the sensitivity and robustness indexes, respectively. Thus, the condition of the frames in progressive collapse improves. Finally, the effect of simultaneous removal of several columns in the progressive collapse of the frames showed that the case 5 of the column removal has the lowest sensitivity index and the highest robustness index, thus having better conditions in progressive collapse.