International Journal of Science, Engineering and TechnologyAuthors: Muhammad Awais, Engr. Danish Saeed, Engr. Zaheer Ahmed
Abstract: Progressive collapse is a disproportionate structural failure in which the localized loss of a critical load-carrying element can cause redistribution of forces, excessive deformation, and subsequent failure of adjacent structural members. An 11-storey regular reinforced-concrete commercial building was developed and analysed using SAP2000 under identical geometric, material, loading, and boundary conditions to ensure a consistent comparison. The Alternate Path Method (APM), following the GSA and UFC approaches adopted in the thesis, was employed by considering three sudden column-removal scenarios: corner-column removal, edge/mid-column removal, and interior-column removal. The structural response was evaluated in terms of vertical displacement, inter-storey drift, axial-force redistribution, bending and shear response, and overall structural stability. The results demonstrated a clear difference among the three structural systems. For the MRF, vertical displacement increased with storey height and reached approximately 0.16 in, with the second column-removal scenario producing the highest displacement response. In comparison, the Diagrid and Outrigger systems showed substantially lower displacement ranges, with their maximum responses occurring in Scenario 3. The MRF also exhibited the highest inter-storey drift, with the plotted response reaching approximately 8 in, whereas the Diagrid system showed a substantially lower drift response of approximately 2.5 in, and the Outrigger system exhibited the lowest drift response, reaching approximately 1.4 in. Axial-force redistribution increased from the upper storeys toward the lower storeys in all three systems. The MRF and Diagrid responses approached approximately 600 kip at the lower levels, whereas the Outrigger system showed a comparatively lower maximum axial-force response of approximately 400 kip. Among the removal cases, Scenario 3 generally produced the comparatively higher drift and axial-force response. Overall, the Diagrid System demonstrated the most favorable progressive-collapse performance, primarily because its triangulated perimeter configuration provides greater stiffness, redundancy, and efficient alternate load paths. The Outrigger System also demonstrated strong performance, particularly in controlling displacement and inter-storey drift through effective load transfer between the central core and perimeter columns. In contrast, the MRF exhibited the least favorable response, characterized by relatively higher deformation and drift.
