Numerical and simplified analytical investigation on RC frame behaviours under progressive collapse scenarios

Although progressive collapse research has been extensively carried out for more than two decades after from the tragic events of 9/11, not many actual dynamic experiments have been conducted due to the constraint in laboratory facilities and expense. Instead, numerical and simplified analytical studies were preferred to achieve a comprehensive understanding of the structural behaviour against these rare dynamic events. In this research, a numerical and analytical investigation programme is carried out to study the mobilisation of alternate-load-path mechanisms, such as compressive arch or catenary action, in RC beam-column substructures undergoing missing column scenarios. First, a physics-based finite element modelling is developed and validated with two published test series conducted under quasi-static and free-fall dynamic conditions. These tests concentrated on 2D reinforced concrete sub-frame structures, investigating two column-loss scenarios, i.e. internal and penultimate columns. After being validated, the model is then employed to further investigate important parameters which can significantly affect the behaviour of a 2D frame structure under both static and dynamic environments, such as concrete grade, release time, column pre-loaded force, etc. Thereafter, a simplified analysis using an equivalent SDOF system is developed to provide a convenient tool for assessing dynamic capacities of RC frame structures. The simplified method produces conservative predictions compared to actual tests and detailed numerical analyses, however it requires very little computing time.