Experimental Study on Response and Failure of Short Reinforced Concrete Beams under Impact Load by Drop Hammer

Reinforced concrete (RC) short beam is the key load-bearing component of buildings. In order to study its dynamic response and failure mechanism under impact load, drop hammer impact tests with different impact mass, impact velocity and impact energy were carried out by combining strain gauge sensor, high-speed photography and digital image technology (DIC). The results show that, the failure forms of the short RC beams under impact loads are arch collapse cracks and overall bending deformation, which are obviously different from those of shallow beams. The axial strain in the mid span of a short RC beam changes from tensile strain to compressive strain. With the increase of impact energy (18 061 J≤E≤49 831 J), the axial peak tensile strain and residual compressive strain in the mid span increase first and then decrease. The short RC beam is in the stage of elastic flexural deformation, elastic-plastic flexural deformation and punching shear failure mode in turn. The crack initiation and propagation process of the short RC beam under impact load is not unidirectional. And the fracture zone is formed by the multidirectional fracture propagation with multiple times, and then the plastic hinge is formed, resulting in the overall short beam failure. The deformation degree of the beam mainly depends on the impact speed rather than the impact energy. Specifically, the peak deflection and residual deflection in the middle span of the beam (26.81 mm≤w_p≤29.85 mm;17.12 mm≤w_r≤21.66 mm) increase with the increase of the impact speed (5.53 m/s≤v≤7.13 m/s) under the same impact energy (30 000 J).