Improving the resistance to progressive collapse of steel and composite frames

Several well publicised examples of progressive collapse have heightened concerns about the need to address robustness as a design requirement. Although research around the subject has been aimed at understanding the mechanics of progressive collapse, little work has been done on translating findings into better guidance on how to ensure adequate resistance without relying on the current prescriptive rules. Based on the Imperial College London method, which provides a soundly based analysis framework for calculating and comparing the performance of different designs, the work presented herein introduces a methodology for making realistic and effective design interventions, in order to allow designers to effectively enhance the robustness of their structure. This strategy is illustrated for both steel and composite frames and covers structures designed for both seismic and non seismic locations. Using the proposed step-by-step methodology, it is possible to redesign a simply designed composite frame in a way that it will be sufficiently robust to cope with any sudden column removal scenario. Comparison with simply increasing tying capacity reveals that the latter does not have a direct and proportional effect on the frame’s resistance and should be used within a more informed context. With the aim of performing a complementary study for moment resisting steel frames, three types of popular welded connections are modelled under progressive collapse loading conditions using the Component Method. Also, an analytical solution for the prediction of the response of irregular beam systems under sudden column loss is presented. Despite the excellent performance of most floor systems, moment frames are found vulnerable to certain column loss scenarios. Thus, these scenarios are further examined with the express purpose of identifying how the frame might best be configured so as to provide the necessary resistance. The findings show how design for seismic resistance and design to resist progressive collapse do not necessarily align and highlight which structural properties are the most important to consider in each frame type, therefore encouraging the use of the proposed redesigning methodology, which is capable of effectively remediating robustness by efficiently addressing localised weaknesses.Open Acces