The Effect of Plan Geometry on Progressive Collapse of Tall Buildings with Diagrid Structure Based on Nonlinear Static and Dynamic Analyses

So far, several studies have been conducted on progressive collapse of tall buildings, of which a few have been on the buildings with diagrid structures, however, in none of them the effect of the building’s plan geometry has been a concern. In this study the progressive collapse of a set of 50-story steel buildings with diagrid structures in three different plan geometries of square, rectangular, and octagonal was investigated by nonlinear static and dynamic analyses. First, the considered buildings were designed according to ASCE 7 and AISC design provisions, trying to be close as much as possible to the optimal design, based on the demand to capacity ratios. Then, five damage scenarios were considered including removal of columns and/or diagonal elements of the diagrid structure in the lowest, the 25th, and the top story of the building according to UFC provisions. Nonlinear static and dynamic analyses were conducted by Perform-3D software. Results show that robustness index, calculated by using the stiffness method would be smaller for the cases of member removal in upper stories, and that the lowest robustness index corresponds to removal of two corner columns, and bracing element connected to them, in the first and second stories. Results also show that removal of interior column in the first story leads to progressive collapse in all three plan shapes. However, yielding and ultimate load factors in building with octagonal plan are more than other two buildings, implying that this type of buildings have more resistance against progressive collapse.