Effects of a Precursor Shock Wave on Blast Loading of a Structure

摘要

A 6- by 6- by 20-ft structure located at a distance of 2000 ft from Ground Zero (GZ) was subjected to a precursor wave from the Priscilla shot, a 37-kt balloon shot detonated at an altitude of 700 ft. The wave struck a 6by 20-ft face of the structure with a peak incident overpressure of between 24 and 26 psi. Free-field measurements of overpressure, dynamic pressure, and force were made at the same radial distance about 25 ft from the end of the structure. Local asymmetries in the blast wave gave different incident conditions for points separated on a fixed radius by only 35 ft. Dust concentrations and dust momentum flux were higher close to the ground than at the 10-ft-high gauge station located near the structure and contributed significantly to the blast loading on the front of the structure. This dust was accelerated through a high-velocity flow that feeds downward to the lower layers. The unusual oscillation seen in records of overpressures on the structures in earlier tests was again observed. A relation between the incident overpressure and the ratio of the impulse on the structure to the incident impulse is suggested. Similar measurements were made on a 9 2/3- by 11- by 17-ft structure located at a distance of 1150 ft from GZ, where the peak overpressure was 87 psi. (Author)