Investigation of air-blast effects from spherical-and cylindrical-shaped charges

Although the distributions of peak incident overpressure and impulse generated from spherical charges and cylindrical charges of the same weight can differ greatly close to the point of detonation, spherical charges are assumed for nearly all explosive-effects computations per modern standards for blast-resistant design such as UFC-3-340-02 and the soon-to-be published ASCE Standard for the Blast Protection of Buildings. A blast-testing program was performed using a reinforced concrete slab as the target to investigate the reflected peak overpressure and impulse distributions as a function of charge shape, orientation, and scaled distance. The charge shapes were cylindrical and spherical, and the charge mass varied from 0.24 to 8.0 kg. Nine pressure transducers were installed on the surface of the slab to record the distribution of pressure histories over the face of the target. A finite element model of the explosive and the target was validated using the experimental data. The validated model was then used to undertake a parametric analysis to more broadly study the effects of detonation point, ratio of charge length to charge diameter, charge orientation and standoff distance on the distribution of reflected overpressure. Numerical results are compared with predictions of UFC-3-340-02. For cylindrical charges, the ratio of charge length (L) to diameter (D), the orientation of the longitudinal axis of the charge, and detonation point within the charge affected the distributions of reflected peak overpressure and impulse in the immediate vicinity of the explosive. The UFC-3-340-02 underpredicts substantially the reflected peak overpressure and impulse on a target aligned with the vertical axis of a cylindrical charge with an aspect ratio of 1.0.