On the influence of charge shape, orientation and point of detonation on air-blast loadings

Charts in the UFC-3-340-2 design manual are used to compute peak incident overpressures and impulse generated by a detonation of an explosive as a function of scaled distance and angle of incidence. These charts assume either a spherical or hemi-spherical charge and do not account for the variation in charge shape, charge orientation and the point of detonation within the charge. A numerical study was performed using AUTODYN to study the influence of charge shape, charge orientation and point of detonation within the charge on the free-field overpressure distributions and the response of an A992 Grade 50 W14 × 257 column. A set of analyses was performed with cylindrical charges with different aspect ratios. Results were compared with those involving a baseline analysis of a spherical charge. The resulting peak incident overpressure and impulses, and the pressure contours were compared in the near-, mid- and far- fields. In the near-field, the overpressure distributions are influenced significantly by charge shape and the point of detonation in the charge. The influence of these variables diminishes with distance. The loading and subsequent response of the W14 × 257 column to a near-field detonation showed significant dependence on the charge shape and charge orientation and clearly demonstrated that SDOF assumptions are inappropriate for blast-resistant design against detonations of improvised explosive devices at small standoff distances.