Air-Blast Effects on Structural Shapes of Finite Width

In blast engineering, many designs begin with simplified hand procedures with the loading parameters determined based upon a reflective surface of infinite size. Individual structural members such as columns have finite widths and should be considered as finite surfaces for blast loading calculations. A study was performed to investigate the effect of finite flange width on blast loadings on structural components. The diffraction of a blast wave around the leading edges of the cross section and the propagation of rarefaction waves from the leading edges to the column centerline leads to a more rapid reduction in reflected pressure than that of an infinite surface: a process that is widely known as clearing. A series of analyses were performed using the computational fluid dynamics code Air3d. Peak reflected pressures are not changed by the “finiteness” of the section, although the reflected impulse can be substantially reduced by clearing. For a given charge mass, held constant for a range of stand-off distances, $R$ , impulse is approximately proportional to $1/R$ when considering an infinite surface. If clearing is considered, the reflected impulse is still proportional to $1/R$ , but can be 50% lower than the value computed for an infinite surface, which has significant implications for blast resistant design of structural components.