Experimental and numerical simulation study on failure mode transformation law of reinforced concrete beam under impact load

Abstract

Changes in the primary influencing factors, such as structural configuration and impact energy, have an influence on the impact dynamic response and failure modes of reinforced concrete beams. In this paper, drop hammer impact tests with different reinforced concrete beam configurations and various impact conditions were conducted. Additionally, parameters of impact force, support force, reinforcement strain, concrete strain, impact local deformation and overall structural deformation were obtained by comprehensive measurements. On the dynamic response and failure modes of reinforced concrete beams, the effects of various concrete strengths, longitudinal/stirrup configurations, hammerhead shapes, and impact velocities were examined. LS-DYNA was applied to perform numerical simulations of reinforced concrete beams with various impact velocities, tensile longitudinal reinforcement ratios, and stirrup ratios. The result of the experiment proved that the peak displacement and residual displacement of reinforced concrete beams under low velocity impact increased with the improvement of impact velocity. Besides, the peak displacement and residual displacement were approximately linearly related to the ratio of impact kinetic energy to ultimate static bearing capacity. The higher the concrete strength and the greater the longitudinal reinforcement ratio were, the larger the peak impact force on the beam was under the equal impact conditions, whereas the smaller the overall displacement response was. The support force, midspan deflection, and residual deflection were less impacted by the form of the hammer head. However, the peak impact force was significantly influenced. Four failure modes of a beam under impact are assessed in accordance with the failure limit state of the structure: bending failure, bending-shear failure, shear failure, and punching failure. According to the test findings, with the improvement of impact velocity, the reinforced concrete beam went from bending failure to bending shear failure, shear failure, and punching failure under the same structural arrangement. By raising the concrete strength and stirrup ratio or lowering the longitudinal reinforcement ratio, the failure mode of the beam progressively changed from punching failure to bending failure while the impact velocity was the same. Through numerical simulation, it was found that the impact velocity of the falling hammer had the greatest influence on the failure mode of the reinforced concrete beam, followed by the ratio of the tensile longitudinal reinforcement, and the smallest was the stirrup ratio.