Loading rate effects on the responses of simply supported RC beams subjected to the combination of impact and blast loads

Abstract

This paper investigates the residual capacities and damage states of simply supported RC beam subjected to the combination of a close-in explosion loading with varied-rate impact loadings using the finite element (FE) simulation through LS-DYNA. Two damage indices on the basis of the residual shear and flexural capacities of the RC beams are proposed. Different loading phases are investigated to assess the sensitivities of the RC beams to the impact loading rate when they are subjected to different combination modes. The combination modes vary in terms of two key loading-related parameters, i.e. the loading sequence and the time interval (i.e., the time lag) between the onsets of impact and explosion loadings. From the FE simulation results, the severity of spallation increases in the beams, when the impact loads are applied prior to the detonations and particularly when the impact loading rate is higher in the combined actions. However, the increase of impact velocity in the combined loadings where the explosion loads are applied prior to the impact loads will lead to direct shear failures near the beam supports. Moreover, the beam experiences more severe damages and greater residual displacements under combined loadings when the sequential detonation is initiated at the time of the peak mid-span displacement is reached. Besides, larger shear forces are produced under combined loadings where the explosion is initiated at the time of the initial peak of impact force. In addition, it is found that the shear and flexural mode based damage indices are more sensitive to the increase of the impact velocity for the combined loading scenarios, where the explosion loads are applied simultaneously with the initial peak of impact force or the peak mid-span displacement, respectively.