考虑柱纵向钢筋屈曲特征的修正材料本构模型

纵筋屈曲会加速钢筋混凝土(RC)柱峰值后承载力退化,在钢筋的材料本构关系中合理地考虑屈曲效应是RC柱的有限元模型可信的基础之一。Gomes等提出的屈曲钢筋材料本构模型(G-A模型)力学概念清楚,但两个基本假定存在明显误差。在OpenSees平台上,采用基于纤维截面的集中塑性铰非线性梁柱单元对24个钢筋试件的屈曲受力性能循环加载试验进行模拟。基于有限元计算结果,对G-A模型采用的全截面塑性弯矩M_p、忽略杆件轴向变形的几何关系进行了误差分析。通过回归分析,建立了修正G-A模型。研究结果表明,屈曲钢筋试件关键截面的应力分布与G-A模型的全截面塑性基本假定差别较大,忽略轴向变形影响会导致屈曲钢筋跨中侧向位移计算结果存在误差。原始G-A模型的模拟效果较差,修正G-A模型对全截面塑性弯矩、几何关系均进行改进,其计算精度明显提高。

A MODIFIED CONSTITUTIVE MODEL CONSIDERING THE BUCKLING BEHAVIOR OF LONGITUDINAL REINFORCEMENT IN RC COLUMNS

The buckling of longitudinal steel bars always accelerates the deterioration of post-peak strength capacity of reinforced concrete (RC) columns. The reliability of the finite element model of RC columns depends on reasonably considering the effect of buckling in the constitutive relationship of bars. The constitutive model of buckled bars proposed by Gomes et al. (G-A model) has explicit physical meaning. However, obvious errors exist in the two basic assumptions. Finite element calculation of cyclic loading tests on the buckling behavior of 24 steel bar specimens was carried out on the OpenSees platform by using fiber section-based plastic hinge nonlinear beam-column elements. Based on the results of the finite element analysis, the errors of the two basic assumptions in the G-A model are analyzed, namely the plastic bending moment M_p and the geometric relationship of ignoring the axial deformation of the member. A modified G-A model is established on the basis of the regression analysis. The results show that the stress distribution on the critical section of a buckled bar is quite different from the plastic bending moment assumption adopted in the G-A model. The errors in calculating the mid-span lateral displacement of buckled bars were introduced by ignoring the axial deformation. The simulation results of the G-A model is less effective. The modified G-A model corrects the plastic bending moment and geometric relationship, and the calculation accuracy isobviously improved.