单轴压缩条件下普通混凝土柱的峰后非线性尺寸效应

Size-dependent nonlinear post-peak stress-strain curve of normal concrete in uniaxial compression

将单轴压缩条件下遭受到剪切带(峰值应力之后呈现线性应变软化行为)形式的单一剪切破坏普通混凝土试样的峰后应力-应变曲线斜率的解析解推广为非线性情形.在峰值应力之前,采用Scott模型描述非线性的本构关系.剪切带的非线性应变软化本构关系由导出的最短普通混凝土试样峰后斜率反算.利用得到的峰后本构关系,对其他较长的普通混凝土试样的应力-应变曲线进行了预测.预测的峰后应力-应变曲线依赖于试样的高度,且与实验结果吻合.估算的剪切带内部平均塑性剪切应变远大于在单轴压缩条件下测得的轴向应变的极限值.若测得的峰后应力-应变曲线被视为本构关系,则普通混凝土柱的峰后延性将被极大地低估.

The analytical solution to the post-peak slope of the stress-strain curve of a uniaxially compressive concrete specimen subjected to single shear failure in the form of the shear band exhibiting linear strain-softening behavior beyond the peak stress was generalized as the nonlinear case. Prior to the peak stress, the Scott model was adopted to describe the nonlinear constitutive relation. The nonlinear strain-softening constitutive relation was back-calculated from the derived post-peak slope of the shortest normal con- crete specimen. Using the assessed post-peak constitutive relation, the stress-strain curves of other longer normal concrete specimens were predicted. The predicted post-peak stress-strain curves are size-dependent and agree with previous experiments. The assessed average plastic shear strain in the shear band is extraordinarily greater than the maximum axial strain measured in uniaxial compression. If the measured post-peak stress-axial strain curve is seen as a constitutive relation, then the post-peak ductility of concrete columns will be greatly underestimated.