钢筋混凝土梁冲击动力响应和破坏模式转化试验研究

随着结构配置和冲击能量等主要影响因素的变化，钢筋混凝土梁的冲击动力响应和破坏模式会发生转化。开展不同配置的钢筋混凝土梁的落锤冲击试验，综合测量获得冲击力、支座反力、钢筋与混凝土应变、冲击局部与结构整体变形等参数，重点分析不同混凝土强度、不同纵筋/箍筋配置以及不同冲击速度对钢筋混凝土梁的动力响应以及破坏模式的影响规律。试验表明：低速撞击下钢筋混凝土梁的位移峰值、残余位移随冲击速度的提高而增大，均与冲击动能与极限静承载力之比存在近似线性关系；混凝土强度越高、纵筋配筋率越高，相同冲击条件下梁所受的撞击力峰值越大，但整体位移响应越小；配箍率的变化对结构的局部响应和整体响应的影响均较小；结构受到撞击时剪切效应在前，弯曲效应在后，斜裂缝先于垂直裂缝出现；依据结构的破坏极限状态，判断梁在冲击作用下存在的弯曲破坏、弯剪破坏、剪切破坏和冲切破坏等4种破坏模式，结果表明：相同结构配置条件下，随冲击速度的不断提高，钢筋混凝土梁由弯曲破坏向弯剪破坏、剪切破坏和冲切破坏转化；冲击速度相同时，提高混凝土强度、配箍率或降低纵向钢筋配筋率，梁的破坏模式逐步由冲切、剪切破坏向弯曲破坏模式转化。结构的冲击破坏模式及其转化规律能够为结构的抗撞设计与防护提供参考。

Experimental study on dynamic response and failure mode transformation of reinforced concrete beams under impact

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.