Probabilistic Progressive Collapse Analysis of 3D Steel Moment Frame Using Fragility Curves and Double-column-damage Approach

In this research, a method of probabilistic analysis of progressive collapse has been introduced based on the concept of fragility curves. In order to develop the fragility curves, the stiffness of two columns is considered as the random variable and the displacement at top of the removed columns is considered as the Damage Index (DI). Based on these measures, the fragility curves of a 4-story steel structure with Intermediate Moment Frame (IMF) system were developed. Six scenarios of progressive collapse were investigated including removal of corner, perimeter, and middle double-columns. The simulations were performed using OpenSees software. The structural analyses were performed using nonlinear time history approach in a three dimensional framework. The results showed that the IDA capacity curve of the lower stories is weaker than the upper stories. According to the results, at each considered DI and assumed performance level, damage to the removed double-columns occurs at more stiffness in the upper stories compared to the lower ones. The results showed that considering the floor slab can reduce the probability of fragility of structures. The effect of the floor on the lower stories of the structure is more than on the upper stories. The increasing effect of floor on the structural fragility corresponding to the first to fourth stories are 13, 9, 6, and 2%, respectively. The probability of exceedance of the performance levels of IO, LS and CP is almost zero until the reduction of the double-column stiffness is 50, 70 and 75%, respectively.