Failure Mechanisms of Multiple External Column Removals in RC Flat Plate Structures

In a reinforced concrete (RC) flat slab structure, the external columns including corner and edge columns on the building perimeter are likely to be more susceptible to abnormal and accidental loads (such as vehicle impact, explosion, fire, etc.) than the interior ones, causing localised damage and a potential progressive collapse of the overall structure. Current research has mostly focused on the case of a single column removal, but due to the uncertainty of the accidental events, the likelihood of multiple columns being simultaneously destroyed is also high. This study will develop a 3D high-fidelity finite element model using the LS-DYNA program, to investigate and analyse the failure behaviour of three 2 × 2 bay RC flat plate substructures with single, two, and multiple column removals: (i) removal of a corner column only (Model C), the accuracy of which will be validated with our previous test results, (ii) removal of a corner column and an adjacent edge column (Model C_1e), and (iii) removal of a corner column and two adjacent edge columns (Model C_2e). The flexural failure, punching shear failure, and post-punching mechanisms of the models will be discussed based on their crack patterns, deformed shapes, and load-deflection responses.