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Current building regulations for design against progressive collapse normally use prescriptive rules and riskbased qualitative scales which are insufficient to cover current needs in design. Structural robustness of concrete flat slab structures is examined using different theoretical models to capture the dynamic behavior under accidental events. In such extreme events, the large dynamic reactions at the connections could potentially lead to punching and progressive collapse. Punching formulae based on load-deformation response relationships such as the Critical Shear Crack Theory (CSCT) are particularly useful in dynamic situations. The Ductility-Centred Robustness Assessment developed at Imperial College London is also used in this paper to derive simple design formulae to assess punching of adjacent columns in the sudden column removal scenario which is commonly adopted in practice. The approach can be extended to assess flat slab systems upon considering membrane action in the slab and post-punching behavior in the connections. Analytical models for tensile membrane are used in combination with the CSCT to demonstrate that the tying forces required in codes of practice cannot be achieved without prior punching of the connections. It is also shown that numerical modelling of post-punching is a promising tool to review detailing provisions for integrity reinforcement.

Previous studies have demonstrated that reinforced concrete flat slab structures could be vulnerable to progressive collapse. Although such events are highly dynamic, simplified static analyses using the sudden column loss scenario are often used to gain an indication into the robustness of the structure. In this study, finite element analysis is used to replicate column loss scenarios on a range of RC flat slab floor models. The model was firstly validated against the results of scaled slab experiments and then used to investigate the influence of different geometric and material variables, within standard design ranges, on the response of the structure. The results demonstrate that slab elements are able to effectively redistribute loading after a column loss event, and therefore prevent a progressive collapse. However, the shear forces to remaining columns were 159% of their fully supported condition and increased to 300% when a dynamic amplification factor of 2.0 was applied. It is shown that this can potentially lead to a punching shear failure in some of the slab elements.