Design-Oriented Approaches for Progressive Collapse Assessment: Load-Factor vs. Ductility-Centred Methods

This paper provides a comparative evaluation of a recently proposed ductility-centred approach for progressive collapse assessment against more conventional design approaches based on nonlinear static analysis with adjusted load-factors. Several typical structural systems are considered for this purpose, incorporating characteristic elasto-plastic responses with/without tensile catenary and compressive arching actions. It is shown that the ductility-centred approach offers a more rational treatment of sudden column loss scenarios in progressive collapse assessment, particularly when reliance is placed on strength reserves such as due to catenary and arching actions. This approach requires additional knowledge of the ductility supply in connections, though it is contended that ductility parameters should indeed be part of the design specification for structural robustness, particularly given the significant variability in the ductility supply of components which might otherwise have similar strengths. While some recent load-factor approaches also attempt to incorporate ductility considerations, these approaches lack generality and can be unsafe depending on the nature of the underlying nonlinear static response. Importantly, it is shown that the explicit treatment of ductility issues can be undertaken within a practical design-oriented framework which is not overly complicated in comparison with load-factor approaches, thus offering a strong case for the adoption of the proposed ductility-centred approach in design practice.