Abstract: According to the theory of the basic mechanics. the mechanical mode of the concrete column with reinforced around the section was predigested. The force balance equation and torque-equilibrium equation were presented by derivation. The deviation of cenler axis in the crazing cross-section of the bridge pier in the course of earthquake was analyzed The conception of the additional moment of center axis was adopted , and the cause of the additional moment of center axis and its influence on the mechanics and the whole stiffness of column were discussed. The results show that , in a certain sense , the additional moment of center axis could offset the horizontal defoτmation of column with reinforced around the cross-section; and could restrain the cross-section to crack and defer the degradation of stiffness. And it is recommended that the additional moment of center axis should be considered in the seismic analysis of the stmcture.

Key words: bridge engineering, additional moment of center axis, whole stiffness, reinforced concrete pier and column

摘要： 以基本的力学理论为基础，简化了四周布筋混凝土桥墩的受力模式，推导出墩身截面的力学平衡方程及力矩平衡方程；分析了在受地震作用过程中桥墩墩身开裂截面形心轴的偏移情况；应用形心轴附加弯矩的概念，分析了形心轴附加弯矩产生的原因及其对墩柱受力和整体刚度的影响。研究表明：在一定程度上，形心轴附加弯矩能够抵消墩柱的部分侧向变形，能够抑制截面开裂、减缓刚度退化。建议在结构抗震分析中应考虑形心轴的附加弯矩。

关键词: 桥梁工程, 形心轴附加弯矩, 推导, 整体刚度, 钢筋混凝土墩柱