Uncertainties in Blast Loads on Structures

The first step in protecting the occupants of a building from the effects of the detonation of an explosive device by a terrorist is to determine the maximum charge weight that the terrorist could reasonably be expected to use. The next step is to determine a set of possible detonation locations that could cause critical design loads on the structure. For each charge weight and location selected, the design engineer typically uses design-manual-, engineering-code- or hydrocode-calculations to predict a deterministic set of pressure-time histories at various locations on the building. The load prediction method used depends primarily on the complexity of the explosive structure geometry. For simple geometries (an explosive charge placed on the ground at a reasonable standoff distance in front of a flat-faced building), the design manual or engineering code approaches are appropriate. For more complicated structures, or for structures very close to other structures, hydrocode calculations may be needed to accurately predict the loads because of shock wave reflection of other structures. Once the loads are predicted, a deterministic dynamic analysis is then performed to predict the response of the building.