Numerical modelling of reinforced concrete columns subjected to close-in explosions

Buildings in the public transport sector, such as railway stations or airport terminals, are potential targets for terrorist attacks. The structural consequences highly depend on the robustness and redundancy of the structure, where a progressive collapse is the doom scenario. Critical load effects may particularly occur when an explosive detonates nearby important structural members. In this study, the response of Reinforced Concrete (RC) columns in existing buildings subjected to a close-in explosion is investigated. One crucial step is to gain a proper understanding of the damage caused by a close-in explosion to RC columns. This is obtained through a combined experimental and numerical investigation. Experimental tests were performed where a high-explosive charge is placed above a simply supported RC square column. This test shows that the column is heavily damaged near the charge location while at both ends, the column is mostly intact. Numerical calculations were performed using LSDYNA, simulating the detonation and column response, where the RC column was modelled with Lagrangian elements and the surrounding fluids (detonation products and air) were modelled with Eulerian elements. Full coupling between the structure and fluid was employed. The test was used to validate the finite element modelling approach. Comparison of the damage in the column reveals a good resemblance with the experiment in terms of the location, size and shape of the damaged concrete zone. Subsequently, the validated numerical approach was applied for a realistic case of a column with surrounding structural elements. The model of this realistic case consisted of the attacked column, a protective jacket around the attacked column and substructure parts like floors and an underlying column including a capital. This example case revealed damage beyond the attacked column in the substructure. This example case demonstrates the need for complete system evaluation, rather than isolating a single element.