Global system considerations for progressive collapse with extensions to other natural and man-made hazards

One of the most frequently used approaches for minimizing the potential for progressive collapse in buildings is the alternate path method. The appeal of this method is primarily due to its relative simplicity and threat independent specification. Applications of the alternate path method typically employ a component design strategy in which the adequacy of the system is based on individual structural components successfully satisfying the acceptance criteria. This design philosophy is also used in evaluating other extreme loading conditions such as seismic loads and direct blast loads. However, the adequacy of the global structural system is not usually investigated during this component design process. This paper details the importance of investigating global effects when evaluating the potential for progressive collapse in buildings. There are two types of frames that will be evaluated: moment-resisting (sway) frames and nonsway frames that include lateral-force resisting elements, such as shear walls. The necessity for considering the global response of a damaged structure becomes apparent following the evaluation of the overall stability of these systems. In addition, the conclusions concerning progressive collapse investigations will be generalized for application to seismic and direct blast hazards. A simple design and analysis method will be introduced, along with the associated acceptance criteria.