Numerical Determination of Equivalent Reflected Blast Parameters Acting on Circular Cross Sections

A number of experimenters observed that the blast shockwave loads experienced by circular cross sections were lower than the predicted loads. These observations revealed a gap in the understanding of the interaction between blasts and structures. The question of quantifying these reduced loads for purposes of analysis and design presented itself for investigation. This paper presents the numerical investigation of the blast reflection reduction due to diffraction around a circular cross section using the commercial software ANSYS Autodyn. The investigation focused on the effects of the cross section's diameter and the explosion's scaled distance on the reflected blast pressure and impulse. Nine numerical gauge points recorded pressure-time and impulse-time histories at regular radial intervals around the front quarter of the circular section. The model's results agreed with incident and reflected pressure and impulse design values. The results indicated that as the diameter of the section increased the peak reflected pressure and impulse at the point of incidence rapidly approached the design values. The results also indicated that both the pressure and the impulse varied sinusoidally between a maximum at the point of incidence and a minimum, approximately equal to the incident pressure and impulse, at the side of the section. Using a sinusoidal curve fit to obtain equivalent reflected pressure and impulse values showed that the actual pressure and impulse acting on a circular cross section were approximately half the recommended design values. The results supported the obvious advantages of designing circular members to resist blast loading. Simplified equations are proposed for calculating the equivalent pressure and impulse acting on circular sections from the standard design values.