This thesis proposes enhancements to the rational robustness assessment frameworks recently developed at Imperial College London, namely the performance-based ductility-centred framework for disproportionate collapse assessment under ‘notional member removal’, and the novel horizontal tying force method to replace current ‘prescriptive tying force’ requirements.
Within the option provided by the ductility-centred framework to assess building structures under sudden column loss by simply providing the nonlinear static response of a planar beam sub-system, the first part of the research involves the development of a practical numerical modelling approach for reinforced concrete planar beam sub-systems. Compared to modelling approaches available in literature, the proposed approach benefits from representing, at a relatively low computational cost, the bond-slip between the concrete and the reinforcement throughout the structural member. The proposed modelling approach is demonstrated to predict, with reasonable accuracy, the development of cracks and the ductility limit of reinforced concrete beam sub-systems.
The second part of the research addresses some of the current limitations of the recently developed novel horizontal tying force method, including i) the proposal of a simplified analytical approach to predict the planar restraint stiffness of floor systems under column loss, including the influence of compressive ring action in the affected floor slab; and ii) the adaptation of the horizontal tying force method to floor systems under corner column loss.
The conservatism of the current tying method is successfully reduced with the analytical approach considering the influence of the compressive ring. Furthermore, the method developed for corner floor systems demonstrates a more significant mobilisation of tensile membrane action than anticipated in current flexure-based assessment methods, offering a novel view on the research and design of corner floor systems against disproportionate collapse.