Air-Blast Effects on Structural Shapes

Keywords: Air blast loads.  Structural shapes.  Numerical analyses.  Computational fluid dynamics.  Peak reflected overpressure.  Peak reflected impulses.  Infinite widths.  Wave propagation.  Blast waves.  Empirical data.  Net pressure loadings.  Standoff distances.

Abstract: This report investigates the effect of short-duration blast loadings on structural shapes of finite width. A series of numerical analyses on W-shapes are performed using a computational fluid dynamics code. Results such as peak reflected overpressure and reflected impulse are compared to values computed using empirical data reported in the literature for reflecting surfaces of infinite width. Significant reductions in loading are observed. The finiteness of the width dimension allows a low pressure wave to propagate inwards on the front surface of the section, lowering the pressure more quickly than if the section had infinite width. As the blast wave engulfs the section over its width and depth, there is a component of positive pressure on the rear face of the section that opposes the positive pressure on the front surface, which can substantially reduce the net pressure loading below that computed using empirical data. The percentage reduction varies as a function of the size of charge and standoff distance, with the largest reductions observed for small charges and large standoff distances.