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Abstract:
By changing the main influencing factors such as structural configuration and impact energy, the impact dynamic response and failure mode of reinforced concrete beams would change. Drop hammer impact tests of reinforced concrete beams with different configurations were conducted, and the parameters of impact force, support reaction, reinforcement and concrete strain, impact local deformation and overall structural deformation of the structure were obtained by comprehensive measurements. The influence law of different concrete strength, different longitudinal reinforcement/stirrup configuration, and different impact velocity on the dynamic response and failure mode of reinforced concrete beams was thoroughly analyzed. The result of the experiment proves that the peak displacement and residual displacement of reinforced concrete beams under low-velocity impact increase with the improvement of impact velocity. Moreover, the peak displacement and residual displacement are approximately linearly related to the ratio of impact kinetic energy to static ultimate load. The higher the concrete strength and the greater the longitudinal reinforcement ratio are, the larger the peak impact force on the beam is under the equal impact conditions, whereas the smaller the overall displacement response is. Changing the stirrup ratio has little effect on the local response and the overall response of the structure. When the structure is impacted, the shear effect occurs first, the bending effect occurs last, and the oblique crack appears before the vertical crack. 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 results, with the improvement of the impact velocity, the reinforced concrete beam changes from bending failure to bending shear failure, shear failure and punching failure under the same structural arrangement. By increasing the concrete strength and stirrup ratio or decreasing the longitudinal reinforcement ratio, the failure mode of the beam gradually changes from punching failure to bending failure under the same impact velocity. The impact failure mode and its transformation law can provide important reference for anti-collision design and protection of structures.
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