Robustness by design - Simplified progressive collapse assessment of building structures

This paper provides an overview of recent developments in robustness design, focussing on the mitigation of progressive collapse in multi-storey buildings. It is argued that rational robustness design should be based on realistic local damage scenarios, structural properties that are within the control of the designer, and an assessment method that establishes the effects of local damage on the specified structure, balancing accuracy, simplicity and efficiency. In this context, sudden column loss is proposed as a realistic local damage scenario for building structures, offering a realistic upper bound for design purposes compared to column damage by extreme dynamic loading such as blast. Furthermore, it is advocated that economic structural design for robustness must rely on strength and ductility, thus stretching the design envelope from the conventional strength limit state to the ductility limit state. Of course, the success of this shift in design methodology for robustness requires the designer to have additional control over the specification of ductility for individual structural components. Finally, design-oriented approaches for progressive collapse assessment are reviewed, focussing on approaches which deal with sudden column loss and ductility issues. In particular, the simplified framework recently developed at Imperial College London is shown to offer a rational multi-level approach for progressive collapse assessment, combining simplicity with accuracy, and accounting for ductility, redundancy, energy absorption and dynamic effects all within a single measure of structural robustness.