Progressive collapse in steel moment frame structures: multi-parameter study

Progressive collapse due to unexpected accidents usually begins with the collapse of one of the main members of the structures, such as a column or a load-bearing wall. The collapse expands the entire structure by creating additional loads on the members and connections attached to the collapsed member. In this research, various scenarios of single-column-removal (5 cases) and double -column-removal (6 cases) in 4, 8 and 12-story structures with steel moment frames were investigated in OpenSees software. The simulation was done in a 3D macro-modeling manner. The nonlinear behavior of materials and geometry were taken into account. Moreover, the vertical effects of the composite floors were considered as double-line springs at the beam to column joints. The results showed that the structures are vulnerable to progressive collapse. According to the results, as the number of stories of the structure decreases the damage caused to the structure is increases. In this regard, the displacements occurred in the corner single-column-removal (Scenario 1) were 70, 56 and 51 mm for 4, 8 and 12 story structures, respectively. The double-column-removal compared to single-column removal greatly increases the structural damage. So that in an 8-story structure, the ratio of maximum displacement of the corner double-column-removal (Scenario 11) compared to the corner single-column-removal (Scenario 1) is equal to 3.7. Furthermore, the impact of the composite floor in the single- and double-column-removal scenarios can reduce the vertical displacements by 40% and 60%, respectively. Finally, the joist beams direction in the composite floor can be effective in reducing the vertical displacements.