Investigating the failure behaviors of RC beams without stirrups under impact loading

This study visualizes the evolution of crack patterns for simply-supported RC beams under static and impact loadings using the techniques of DIC and high-speed camera. At relatively low impact velocity, we observe multiple flexural cracks developing in a progressive sequence from mid-span to supports. At relatively high impact velocity, we observe a shear plug initiated at loading point during early time before impact response reaching supports. The critical velocity for transition from flexural- to shear-failure mode varies from 6.9 to 8.4 m/s. Comparative analysis suggests the impact resistance is related to failure modes: The maximum impact force is controlled by global resistance of structure at flexural-failure mode, while it is controlled by local failure of materials at shear-failure mode. Finally, this study compares absorbed energy with impact velocity at flexural- and shear-failure modes. By increasing impact velocity, the results show that absorbed energy increases at flexural-failure mode, and decreases at shear-failure mode. The decreasing absorbed energy capacity is possibly caused by less plastic deformation of steel reinforcements in a more concentrated zone of shear plug at shear-failure mode.