Clearing effects on plates subjected to blast loads

Empirical prediction methods are often used in the early stages of design to quantify the blast load acting on a structure. While these methods are reasonably accurate for geometrically simple scenarios, they may not be accurate for situations where the target does not form a reflecting surface of effectively infinite lateral extent. In this case, the blast wave will diffract around the target edge, leading to the propagation of a relief wave inwards from the edge of the structure, reducing the late-time development of pressure in a process known as ‘clearing'. This paper presents results from a study undertaken to determine the influence of clearing on the response of simple targets. Experiments were conducted in which deflection–time histories were recorded for target plates subjected to cleared and non-cleared blast loads. These were compared with predictions from explicit dynamic finite-element and single-degree-of-freedom models, in which the blast loading was derived by applying a simple correction to the empirical blast prediction method. The results presented show that neglecting clearing may result in highly conservative predictions of target response and that analyses using loading derived from simple corrections to the ConWep predictions match the experimentally observed results very closely.