基于纤维截面的弯剪耦联薄壁墩柱模拟模型

钢筋混凝土（RC）桥墩构件常采用空心截面，震害调查表明其失效模式多表现为弯剪耦联的非线性破坏．本文提出一种基于纤维截面、考虑弯剪耦联变形的混凝土墩柱模拟模型．首先将双轴材料本构引入纤维材料状态的计算，然后通过纤维截面积分，得到适用于Timoshenko梁柱单元的截面刚度矩阵，最终实现考虑弯剪耦联效应的梁柱单元．其中，双轴RC本构模型采用往复软化薄膜模型（CSMM），并对CSMM中单轴混凝土滞回模型进行修正．通过引入纤维间变形协调条件并采用Newton迭代法，确定截面和纤维状态．最后，通过一个缩尺薄壁桥墩构件拟静力试验的模拟分析进行对比验证，分析结果表明该模型精度较高，对弯剪耦联导致的强度和刚度退化以及捻缩效应模拟较好，且计算效率较实体模型高．

Fiber Section Based Flexure-Shear Coupling Analysis Model for RC Thin-Walled Piers

Hollow section piers are often used in reinforced concrete （RC）bridges. It has been proved by earthquake damage investigation that the piers may perform flexure-shear coupling behavior, and eventually lead to pier failure and/or collapse. A fiber-section based RC pier simulation model considering flexure-shear coupling effect was pre- sented in this paper. By introducing bi-axial material constitutive relationship into the determination of fiber deforma- tion status, the sectional stiffness for beam column element can be obtained through the integration of fiber responses. Then the flexure-shear coupling Timoshenko beam element was implemented. The cyclic soften membrane model （CSMM）constitutive relationship was adopted for plane bi-axial RC components in the calculation of the nonlinear characteristic of fibers. The concrete uniaxial material model in CSMM was improved. By assuming the compatibility condition between each fiber and making use of the Newton iteration algorithm, the fiber and section responses were determined. At last, a scaled hollow section pier with quasi-static test result was compared with the numerical model, and the results show good agreement. The strength and stiffness degradation and pinching effect caused by flexure-shear coupling effect are captured by this model. And the fiber model shows sufficient accuracy and computational efficiency.