Abstract: According to Standard (JTJ023-85)of road、bridge and culvert, the beams of the kind of B of partially pretressed concrete and the compression members with small eccentricity, this paper gives the general equations of calculating the value of ξ of a relative height in the com pression reign of the section.And it gives different formulas of the coefficient of these equations.This paper also offers three kinds of simplified approaches by which a cubic equation approximated by aquadratic equqation with acceptable accuracy is proposed.Through examples these simplified methods are analysed and compared.

Key words: neutral-axis, comparison, simplified

摘要： 根据公路桥涵设计规范JTJ023-85,推导了部分预应力砼梁B类构件在计算使用荷载下开裂截面应力时求中和轴位置的一般三次方程,及钢筋砼小偏心受压构件计算中,求受压区高度的一般三次方程.分析了3种解三次方程的简便计算方法,并根据例题进行了分析比较,可供工程技术人员参考.

关键词: 中性轴, 比较, 简化