External blast load on structures – Empirical approach

Modeling structures response to blast loads interests more and more people concerned about industrial accidents and/or terrorism. Today, two approaches are available: one can either use an ALE model (*ALE) with a lagrangian-eulerian coupling (*CONSTRAINED_LAGRANGE_IN_SOLID) or a pure lagrangian approach where an analytical loading of the structure replaces the computation of the propagation. The lagrangian approach allows the use of a much smaller model since only the structure is modeled. This kind of approach, based on the empirical model described in the TM5-855 US army handbook (CONWEP), is currently available in LS-DYNA (*LOAD_BLAST). However, it is limited to the treatment of the explosions of hemispherical charges on the ground or spherical charges in the air without ground interaction. In many cases, the interaction of the shockwave with the ground induces blast reinforcement. CRIL TECHNOLOGY, in order to get more precise blast load evaluation with a pure lagrangian approach, has developed a new user-loading model (evolution from *LOAD_BLAST) to take into account new abacuses for TNT and for reflecting coefficients, ground effects and Mach stem. Major evolutions are based on empirical models described in the TM5-1300 US army handbook. This new user-loading, in many cases leads to more precise and more conservative load while retaining a reasonable model size as the method is purely lagrangian.