Response spectra for explosion resistant design and assessment

This paper describes a project to examine the explosion test results obtained at Spadeadam in the 1990's from the point of view of structural response. At an early project phase, when reliable simulations may not be available, nominal explosion overpressures and durations or past experience from similar situations may be used as inputs to the Response Spectrum approach. The results, however, will only be as accurate as the estimated loading. Structural engineers are often presented with complex pressure traces and are expected to design efficient structures to resist these loads without any further guidance. Response surfaces, representing peak deflection against scaled natural period and structural resistances, have been calculated for a large number of experimental and simulated pressure traces. Biggs response curves are a special case corresponding to triangular loading time histories. The Response Spectra are obtained from these response surfaces by taking horizontal sections of these surfaces at allowable ductility values. The required static resistance for a structure with a given natural period and pre-determined allowable ductility may be read from these curves. The design or assessment may then proceed with this required static resistance which may be reinterpreted as an equivalent static load. The project team has had access to FLACS simulated pressure traces corresponding to the Spadeadarn tests. This has enabled a comparison to be made between experimental and simulated traces taking into account the target structures' characteristics. A description of the method has been included in reference [1], in the Commentary of the new API RP on Fire and Blast which will be made available during 2006, and in a forthcoming OTO (HSE) report.