低速冲击下RC梁的冲切破坏判据

Criterion of punching shear failure for RC beams under low-velocity impact

已有诸多低速冲击试验表明按照现有规范静态受弯破坏设计的RC构件,在冲击作用下会向冲切破坏模式转变。为了明确低速冲击下典型RC梁的破坏模式转变机理及其冲切破坏判据,对6组RC梁落锤冲击试验中构件的弯曲和冲切破坏模式、冲击力、支座反力和跨中位移时程进行数值模拟复现,验证了采用的材料本构模型及参数和数值模拟方法的可靠性。采用已验证的数值模拟方法开展RC梁的冲切破坏机理分析,评估了落锤质量、截面尺寸、冲击速度、混凝土强度、配箍率、纵筋配筋率和剪跨比对冲切破坏模式的影响程度,发现除纵筋配筋率和剪跨比外,其余参数均能改变RC梁的局部速度响应或动态受剪承载力,进而显著影响RC梁的破坏模式。进一步,根据330个落锤冲击工况的数值模拟结果,提出了关键截面的动态剪切荷载V_(d,sd)和动态受剪承载力V_(d,sc)的经验公式,并给出了RC梁冲切破坏判据的显式表达式。通过与71组落锤冲击试验对比,得到该判据对RC梁冲切破坏预测准确率达到90%,可辅助于RC结构的抗冲击性能评估与设计。

A lot of previous low-velocity impact tests have shown that the failure mode of static flexural-dominant RC members designed by existing standards will transfer to punching shear failure under impact load.To make the mechanism and criterion of punching shear failure clear for RC beams under low-velocity impact,the reliability of the adopted constitutive models,parameters and numerical simulation method is verified by numerically recurring the flexural failure and shear failure modes,impact force-,reaction force-,and mid-span displacement-time histories in six drop hammer tests.The mechanism analysis of punching shear failure was conducted by the verified numerical simulation method to assess the influence on punching shear failure mode by drop hammer weight,sectional dimension,impact velocity,concrete strength,stirrup ratio,longitudinal reinforcement ratio,and shear span ratio.The result shows that the above parameters have a significant influence on the occurrence of punching shear failure for RC beams by changing the local velocity response or dynamic shear capacity of RC beams,except for longitudinal reinforcement ratio and shear span ratio.Further,based on the results of 330 numerical simulated scenarios,the empirical formulas of dynamic shear load V_(d,sd) and dynamic shear capacity V_(d,sc) in the key section were proposed,and the explicit criterion of punching shear failure for RC beams was established.The criterion was validated by 71 drop hammer tests(accuracy 90%),which can assist the impact-resistant assessment and design for RC structures.