Redesigning composite frames for progressive collapse

Explicit evaluation and improvement of a building's robustness require taking into account all the main resistance mechanisms, employing realistic failure criteria and obtaining quantitative results based on a suitable level of structural idealisation. The Imperial College London method has made significant progress towards establishing a soundly based analysis methodology for calculating and comparing the performance of different designs. Recent advances have facilitated the execution of extensive parametric studies that are quick to run and thus able to provide comprehensive results. These advanced tools are employed here to examine the robustness of a simplified version of the Cardington test frame and to compare its performance with that of a bare steel equivalent. Both arrangements fail to provide the necessary resistance, with the bare steel being inherently less robust. The paper introduces a step-by-step methodology to determine the most efficient and practically applicable changes, making it possible to redesign the composite frame in a way that it will be sufficiently robust to cope with any sudden column removal scenario. Comparison of the methodology with simply increasing tying capacity reveals that the latter does not have a direct and proportional effect on the frame's resistance. This leads on to consideration of how tying capacity might be used within a more informed context.