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Blast and Impact Loading and Response of Structures
Full Session with Abstracts
Andrew Whittaker, PhD, P.E., S.E., F.ASCE, F.SEI, F.ACI
SUNY Distinguished Professor and MCEER Director
University at Buffalo, Department of Civil, Structural, and Environmental Engineering
Blast-wave clearing is routinely considered to calculate over-pressure loadings on structures and components thereof. When blast waves impinge on a reflecting surface, rarefaction waves are formed from the free edges of the surface, propagate toward the center of the front face, and reduce the reflected overpressures. The clearing time is the length of time required for the reflected overpressure to decrease to the stagnation pressure. Empirical relationships for clearing time are typically used for design calculations, and these were developed from experiments in shock tubes in the late 1940s and early 1950s. The assumption of a planar shock front with a long positive phase duration, produced in a shock tube, although appropriate for a far-field nuclear detonation, is inappropriate for near-field detonations because reflected overpressures on the front face of a target vary with arrival time, standoff distance and angle of incidence, and the positive phase duration is short. CFD simulations of near-field detonations indicate the codified methods for characterizing clearing are incorrect, and that for design, clearing should be ignored.