Keywords: hydro-code, simulation, concrete, explosive blast wave, dynamic response, protective structure, LS-Dyna, Dytran, Autodyn.

The conventional use of concrete as a structural material is mostly for static and quasi-static loading, such as in building, bridges, etc. The design methodology for such loads is well established. In recent years, however, the need to evaluate concrete behaviour under dynamic loading has become increasingly important due to terrorist activities involving explosive charges. The aim of this work is to study the dynamic response of a typical reinforced concrete structure to a nearby detonation of an explosive charge employing various hydro-codes.

An evaluation of three commercial hydro-codes capable of simulating the interaction of explosive blasts with reinforced concrete (RC) structures is presented. Firstly, a simple test case of a simply supported RC beam with a prescribed load was chosen. The results for this simple case were validated against analytical solutions for both elastic response and perfectly plastic, impulsive response. Then, a more complex structure consisting of an inverted U-shape was chosen for blast loading. This structure was reinforced symmetrically with respect to the expected loading, with a typical span of 3 m and a thickness of 200 mm. The choice of this shape was motivated by the simplicity of applying the appropriate boundary conditions to its feet. Two types of loading were employed: (a) a blast wave produced by detonating a 20 kg charge of TNT explosive, at a distance of 0.5 m above its centre, and (b) a contact detonation of 1 kg TNT charge. The response to these loadings was obtained using internal material models of the codes for representing the concrete and the reinforcing bars.

The numerical model employed a full fluid structure interaction between the blast wave and the structure. To this end the blast wave was represented in an Eulerian finite volume mesh, while the concrete was modelled by a Lagrangian solid finite element mesh, with discrete embedded rod elements for the reinforcing bars.

The resulting centre deflection of the structure is chosen for comparing the results of the three simulations. We also checked the sensitivity of the results to various parameters such as overall mesh size and concrete strength. This study enables one to avoid the pitfalls of such simulations by the correct choice of modelling parameters.

The codes produced acceptable results, but it is clear that in order to get a converged and reliable result, fine tuning of the model is necessary. This would involve running the problem with various cell sizes.

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