Multi-Hazard Design to Resist Progressive Collapse

The prevention of progressive collapse through design requires attention to the abnormal state of loading that may produce a localized failure and the response of the structure in redistributing the loads to the undamaged elements. The design requirements for new structures, where the specification of continuous reinforcement and moment resisting connections are reasonable, are not necessarily the most appropriate for the retrofit of existing structures, for which the adaptation of these beneficial details may be a practical impossibility. Therefore, the design practices required to prevent a progressive collapse must be related, on a case by case basis, to the structural system that must be upgraded and the extent of protection that will be provided. A rational approach is presented for determining the appropriate protective design required to prevent a progressive collapse in both new and existing structures. The paper will also discuss the analytical methods that are needed to accurately assess a structure's response to abnormal loading and provide an assessment of different conditions where the Indirect, Specific Local Resistance and Alternate Path methods are most appropriate.