As part of the continuing effort undertaken at Imperial College London to develop a unified measure of robustness, the current study addresses several issues which were identified in the past as prospective enhancements to the ductility-centred framework.udAs robustness evaluates the structural performance against extreme local actions, it should consider within the assessment framework the duration of the accidental event and its repercussion on the structural response. In this context, incorporation of rate-sensitivity is a step forward to a more realistic structural assessment under blast/impact loading. Towards this end, the rate-sensitivity of steel is quantified with the aid of experimental coupon tests. Subsequent studies on rate-sensitivity at the structural level, which similarly include validation by component testing under moderate to high rates, address a knowledge gap on the dynamic over-strength and ductility supply associated with sudden column loss scenarios. Further developments are made to the framework in order to accommodate material rate-sensitivity, where a case study is undertaken which illustrates the diminishing rate effects at higher structural levels.udSince local damage resulting from extreme loading does not revolve around a single possible damage scenario, it is important to investigate other local damage scenarios besides the typically considered single column removal. In this context, the feasibility and practicality of scenarios involving the simultaneous loss of multiple columns are considered, with generalisation of the simplified dynamic assessment and development of simplified models based on dominant modes of deformation. As the study of different damage scenarios moves the discussion on robustness towards rational risk assessment, this work aims to demonstrate the adequacy of the ductility-centred framework to the quantification of the failure probability under column loss scenarios. With an illustrative application study, it is established that such risk assessment is not only feasible but may ultimately provide a valuable decision-making tool in the design process of robust structures.
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