Abstract
The assessment of structural response due to blast loading has become a point of research and interest for blast civil engineers for decades. The aim of this paper is to include the negative phase in the modelling of the blast load and to investigate the effects of underpressure (negative phase) resulting from impact loading of an explosion on structural response. This paper has targeted a typical structure with a high natural period, in other words, a flexible structure. An exponential approach has been used for modelling the pressure-time history of the blast load, where the pressure decays non-linearly. In order to determine the structural deformation, a numerical model of the single degree of freedom system (SDOF) was used. resulting from including the negative phase showed a noticeable reduction in the peak deflection in the case of the flexible structure response. In addition, the reduction factor of structural deformation has increased as the ratio of the ultimate structural resistance to the blast force (Ru/P) has increased. Therefore, the negative phase should be included in the blast load modelling even if it is considered conservative. New modified charts have been extracted, which engineers may use to predict the reduction value in structural deformation if underpressure is added. Reduction charts have been classified based on the structure member property and geometry at any explosion scenario.