基于MFBFE剪力墙单元研究及低周反复试验数值分析

Numerical analysis for low cyclic loading test of shear wall based on MFBFE shear wall element

基于力插值纤维单元是目前钢筋混凝土结构非线性分析最常用的单元,它忽略单元的截面剪切变形,采用平截面假定,但对于剪力墙构件,其截面高度比较大,仍采用平截面假定忽略截面剪切变形将会造成较大的误差。基于这一背景,文中提出考虑截面剪切变形的修正基于力插值纤维单元(MFBFE),其截面不再是平截面,而是曲面,用以模拟剪力墙的地震反应非线性分析。基于OpenSees进行MFBFE单元开发,并对一组9个剪力墙试件进行水平低周往复模拟。实例分析结果显示较好地预测了构件的初始刚度、屈服力、极限力、卸载刚度、残余位移、延性和能量耗散,表明MFBFE单元模拟剪力墙地震反应非线性分析有较高的精度。并且对MFBFE单元在不同轴压比、不同高宽比、不同混凝土强度、不同纵向配筋率、不同约束区长度、不同配箍率下进行趋势分析。数据显示,文中提出的分析模型的适用范围很广,对于上述不同的计算和构造条件下都满足精度要求。

Force-based fiber element, which ignores section shear deformation and assumes the section is plane, is the most commonly used element for the nonlinear analysis of reinforced concrete structures. However, for shear wall structures, the section is much wider than that of beam and column, thus plane-section hypothesis and section shear deformation ignorance will cause greater error. A Modified Force-based Fiber Element （MFBFE） considering the section shear deformation is proposed in this paper. In the modified force-based fiber element, the cross section is no longer plane section but curved surface. The MFBFE elements is first formulated and then implemented in the finite element program OpenSees. Numerical analysis for a group of nine shear wall specimens under low-cyclic loading is conducted using MFBFE element. Analysis results show that the entire hysteretic loops of shear walls, including the initial stiffness, yield strength, ultimate strength, unloading stiffness, residual displacement, ductility and energy dissipation, are well predicted. Trend analysis under variable axial compression ratio, variable aspect ratios and variable concrete strength, variable longitudinal reinforcement ratio, variable constraint zone length, variable stirrup ratio shows that the MFBFE element has broader applicability. The new element proposed in this paper can be used in shear wall structures design to resist earthquake actions.