Blast wave propagation in confined spaces and its action on structures

Abstract

The safety of both military personnel and equipment in unstable regions has for a long time been a major issue and concern. Protective shelters with multiple configurations have been widely used to meet safety requirements. Since military compounds are subjected to di↵erent types of threats, such as explosive devices, it is of utmost importance a good understanding of the response of such shielding structures to blast waves. Accordingly, propagation of shock waves in partially- or fully-confined environments is a complex phenomenon due to the possibility of multiple reflections, di↵ractions and superposition of waves. Yet, being able to derive valid predictions of such phenomena is highly relevant, e.g. when it comes to the assessment of protection of personnel. This study looks at the propagation of blast waves in confined spaces and its action on structures, such as compound survival shelters. Whilst full-scale tests o↵er useful insights, the time and expenses associated with such experiments renders then unpracticable. Small-scale experimental models in combination with the Hopkinson- Cranz scaling laws, however, represent a viable alternative to the study of blast wave evolution. The experimental set-up was designed as a rigid structure and built to have a geometrical reduction factor across all dimensions. Experimental analyses were performed on a small-scale model of the actual configuration of the compound survival shelter subjected to the detonation of an explosive charge at di↵erent locations close to its entrance. Pressure-time signals were recorded on a number of locations in the model and a numerical model, based on the explicit finite element code LS-DYNA, was also developed to complement the experimental programme. The recorded experimental data were compared with the numerical predictions to validate the FE model. The proposed numerical model predicts and captures the relevant stages of the propagation of the shock wave. The study of blast wave propagation, which is di↵erent from the propagation of a shock wave in free-field scenarios, is not completely described in literature, especially when it comes to structural response. A numerical analysis of a single corrugated member was performed to evaluate the influence of several wave related parameters on its structural response, e.g. impulse, multiple positive and negative pressure profiles and signal simplifications. Results indicate that the negative impulse train in the pressure-time history plays a significant role in obtaining an accurate performance of the structure. It was also found that a complex pressure history profile can be reduced to a simplified pulse for structural analysis purposes. The consequence of blast events, namely terrorist attacks, warfare scenarios or accidental explosions, usually means severe damage of structures and loss of life. Pressure-impulse diagrams are widely used as a rapid and intuitive tool to investigate the blast response of structural elements under a number of di↵erent blast scenarios. In this study, a numerical model of a 20 ft steel ISO container was developed using LS-DYNA and the accuracy of its response to blast loading is verified against experimental full-scale test data available in the literature. The results show a good agreement between the experimental data and numerical results. Pressure-impulse diagrams were also derived to correlate the damage criteria under di↵erent blast loading scenarios.