Effect of Initial Local Failure Type on Steel Braced Frame Buildings against Progressive Collapse

In many studies, the alternative load path method (APM) has been used for progressive collapse analysis. In this method, one or several columns of the building are removed and the building response is investigated. This method ignores the initial local failure cause of building and this can affect the structural response. Investigation of ignoring the initial local failure cause of steel braced frames is the main purpose of this research. The variables include the type of progressive collapse investigation (ignoring the initial cause of failure or APM, considering blast loading and the heat caused by the fire as the initial causes of failure) and the location of the initial local failure in plan (outer and inner frame) and in floors (1st, 2nd and 3rd). 4-story braced steel buildings were simulated using ABAQUS software and the responses were compared using different methods. The most important results showed that the axial forces are very noticeable in the columns around the damaged site if the initial local failure caused by explosive loading; while these forces are ignored when APM is used. Therefore, due to this significant difference, if the design of a steel building is to be considered against progressive collapse, it is recommended to consider the initial local failure in order to make the appropriate design in accordance with it. Therefore, the initial loading type has a very significant effect on the structure response, and ignoring the initial local failure can lead to incorrect predictions of the structure response.