Effect of load details of the successive explosions on the blast behaviors of reinforced concrete beams

The objective of this study was to study the effect of load details of successive explosions on the blast behaviors of reinforced concrete (RC) beams. First, the effect of the successive loading of two identical explosions was discussed by considering the influences of standoff distance, charge mass on the failure states, and structural responses (displacement and support reaction force). And keeping the total TNT charge mass of 1 kg unchanged, the effect of loading numbers was investigated by loading two 0.5 kg TNT successively and a single 1 kg TNT on RC beams, respectively. Besides, the successive loading of two different explosions was also considered by investigating the effects of loading sequences and the first explosion induced pre-damage on the ultimate accumulated damage of RC beams. At last, based on the reaction force and displacement responses, a nonlinear relationship between the dynamic residual load-carrying capacity and the accumulated residual displacement was obtained to assess the damage states of the tested beams. The results show that the local failure range along the beam span direction (length of peeling-off and length of spallation) caused by the first blast load did not apparently increase when the damaged beams were subjected to another blast load. With the increase in explosion numbers, depth of compressive crushing increases gradually. At the same stand-off distance (from 0.25 to 0.45 m), due to the damage accumulation effect, successive loading of two 0.5 kg TNT can trigger more severe local failure but smaller accumulated residual deflection to beams than the single loading of a 1 kg TNT. Besides, when two different blast loads are loaded on tested beams, the loading sequence of the larger one first and then the smaller one (1 kg TNT/0.5 kg TNT at h = 0.45 m) can trigger larger damage to beams than the opposite loading sequence (0.5 kg TNT/1 kg TNT at h = 0.45 m). And for the beams subjected to a smaller blast load first and then a larger one, a stiffer behavior may be triggered by the second blast load on the beam after the first loading of the smaller blast load due to the residual strain in longitudinal reinforcement. Furthermore, based on the nonlinear relationship between residual load-carrying capacity and residual displacement, the accumulated damage of RC beams was divided into mainly four phases.