The Influence of the Underpressure Phase on the Dynamic Response of Structures Subjected to Blast Loads

Abstract

The standard approach in protective design is to model blast loads with a triangular pulse shape which is characterized by the peak reflected overpressure and the reflected impulse. The US and European threat levels, GSA and ISO EXV, define pressure-impulse combinations for blast load characterization. However, this approach neglects the underpressure phase. The actual decay of a blast load is nonlinear and can be modeled more accurately with an exponential approach which takes into account the underpressure phase. When considering underpressure effects, however, special attention should be paid to the modeling of the different reflection effects for the over- and underpressure phase. The authors derive a new reflection coefficient for the maximum underpressure. Based on a single degree of freedom system, the authors then determine the influence of the reflected underpressure phase for different systems. Especially for flexible systems subjected to weak blast loads, the underpressure significantly dominates the structural response. In these cases, the standard triangular approach is not on the safe side. This paper presents new demarcation criteria to rapidly assess the influence of the underpressure phase.