Dynamic Response of RC Elements Subjected to Combined Loading of Blast and Fragments

Abstract

Combined loading of blast and fragments involves various loading mechanisms on a structural element. It includes the momentum inflicted by the blast load and the penetration of the fragments, as well as the structural damage due to fragment penetrations. A model to account for the fragmentation loading in a realistic, yet simplified approach was suggested and validated in previous experimental and analytical studies. However, the dynamic response of a structural element subjected to combined loading considering a nonuniform fragmentation distribution has not been studied. A finite-difference model is presented in this paper to solve the dynamic response of a one-way reinforced concrete (RC) element. The simplified method to consider the strain-rate effects in the section (macro) level is proposed. It is based on static analyses of the section at different loading rates, thus making the dynamic solution relatively quick. The model is validated with analytical and experimental data that included blast loads. The finite-difference model is used to simulate the response of a RC element to combined loading. Three design approaches, one of which neglects the fragmentation on the one hand and on the other hand considers a higher magnitude of blast load, are studied. It was shown that for the presented case studies, the fragmentation must be considered for a more realistic prediction of the structural response. For short standoffs, a nonuniform fragmentation distribution should be considered to get more realistic predictions, whereas for larger standoffs, a uniform fragment distribution can be assumed. In both standoff ranges, a design approach that is commonly used, in which the fragmentation effect is neglected, leads to less conservative results.