Assessment the behavior of seismic designed steel moment frames subjected to progressive collapse

Abstract

Recent investigations reveal that progressive collapse phenomenon is dominant behavior in the majority of steel structures. Although the design of buildings is based on the fact that they need to withstand all the loads exerted on the structure, failure occurs as a result of inadequate design and modeling techniques, particularly for abnormal and extreme loading conditions. Once one or more load bearing member is eliminated from the structure, progressive collapse, mainly in columns, will commence. By the time a column is eliminated from the structure as a result of a sudden motor vehicle strike or earthquake or fire or any other internal or external factor that could take one column out of the system, the weight of the building (gravity load) will be distributed among other columns within the structure. Failure commences in the part of the structure that has lost a column unless other columns are designed appropriately against gravity loads and are capable of redistribution of additional loads imposed on them. Failure of vertical load bearing elements will continue until the stabilization of extra loading. Hence, this could lead to serious damage and collapse of the building which will lead to higher damage to the building than the primary damage. This research is based on the regulations conforming to the specifications of UFC guidelines and the structures have been modeled using SAP2000 (2012). In order to study the effects of the progressive collapse on the seismic design of special steel moment frames, SMRF, two 5-story and 15-storystructures are modeled in SAP2000 (2012). In order to have a better understanding of progressive collapse and obtain reliable results, Linear Static (LS), Nonlinear Static (NLS) and Nonlinear Dynamic analyses (NLD) procedure for single and 2 adjacent columns removal have been implemented in this study. Having a good perception of the possibility of progressive collapse involves incorporation of demand capacity ratio, plastic hinges formation and vertical displacements of removed column's location plus axial force in columns adjacent to the removed column. Other factors such as number of stories and the amount of local damage resulted from the removal of 2 adjacent columns could also lead to a better understanding of the structural behavior.