An integral modelling approach for the loading and break-up of RC structures due to internal explosion of fragmenting shells

The Klotz Group (KG), an international group of experts on explosion safety, investigates the debris throw hazard associated with the accidental detonation of ammunition in reinforced concrete (RC) structures. Experiments are combined with engineering models but also with results of advanced computational modeling, which is the topic of this paper. EMI and TNO are establishing a sophisticated three step approach to analyze the explosion phenomena of single and multiple bare and cased charges in a RC ammunition magazine. In the first step the blast loading and gas pressure is modeled by a coupled fluid-structure interaction simulation. The cubicle magazine was modeled in 3D to capture the correct structural failure mode and venting process. The second step consists of fragment trajectory predictions, using fragmentation matrices based on arena test data together with empirical penetration relations to quantify the fragment jetting effects. The simulated blast and fragment loads are the input for the third step on the simulation of the dynamic response and break-up of the structure. In this step the structure was modeled in more detail than in step 1 in order to capture the local failure phenomena and final break-up as good as possible. The approach has been applied to a series of explosion tests with cased and uncased 155 mm charges [1]. Recently a second series of simulations was performed for shells with thin casings, but with the same amount of explosives as in the previous series. In the current paper the background and the results of the three-step approach will be presented and discussed. The loading and break-up process for thin walled 121 mm shells will be presented and analyzed. Special attention will be paid to the sequence, the temporal and spatial distribution of the blast and fragment loading and the consequence of these aspects for the break-up process.