Mitigation of Progressive Collapse in Multi-Storey Buildings

Abstract

This paper describes recent developments in performance-based design of multi-storey buildings against progressive collapse, where particular emphasis is given to practical implementation within the structural design process. The benefits of sudden column loss as an event-independent scenario are highlighted, and its computational merits as well as its correlation with actual extreme dynamic events are emphasised. It is proposed that the robustness limit state should be based on avoidance of failure in the upper floors above the damaged column, where it is proposed that the design envelope should be stretched from the conventional strength limit to the ductility limit so as to achieve economic design for robustness. In addressing the dynamic effects of sudden column loss, load factor approaches that have been recently proposed for use with some new usa design codes are shown to have serious shortcomings, potentially leading to unsafe estimation of dynamic amplification. These shortcomings are effectively addressed by the ductility-centred approach recently developed at imperial college london, which offers a practical multi-level assessment framework for progressive collapse under sudden column loss. Key lessons are drawn from the application of the ductility-centred approach to steel-concrete composite multi-storey buildings, where the inadequacy of prescriptive and load factor approaches is clearly demonstrated, and where the benefits of such factors as connection ductility, additional connection reinforcement, axial restraint, infill panels and rate-sensitivity are highlighted.