Comparison between Alternative Load Path Method and a Direct Applying Blast Loading Method in Assessment of the Progressive Collapse

Extensive research has been focused on the progressive collapse analysis of buildings and most of them are based on the alternative path method (APM) with sudden removal of one or several columns. However, in this method the damage of adjacent elements of removed columns under blast conditions was ignored and this issue can lead to an incorrect prediction of progressive collapse. Therefore, in this study to evaluate the alternative load path method in predicting the progressive collapse due to blast loading, a 3-D finite element model of a 7 storey steel building simulated and the behavior of structure was studied using the direct applying of blast load method and alternative load path method. For simulating and applying the blast loading and assessment of their direct effects on structures, a blast load equivalent to 1 ton TNT was considered at a distance of 4 meters from the corner of the structure. The pressures of this blast in 4 loading cases are applied to the adjacent structural members and the structural response has been examined. Finally, the exciting forces in adjacent structural members of blast site in each case have been compared. The results show that in assessment of the potential of progressive collapse occurrence by considering the blast loading as the initial reason of failure, the structure response will be different compared with the alternate load method that in which the initial reason of progressive collapse was ignored.