中文摘要：

本文指出现行钢岔管基于应力分类的安全评价方法中存在的问题：应力指标的弹性计算方法与安全评价的塑性原理不协调; 提出基于弹性模量缩减法的钢岔管安全评价方法,该法根据下限原理,在弹性迭代获得结构体系的一系列允许应力场过程中,对不同类型单元采用相应的广义屈服准则,利用单元承载比统一衡量所有单元的承载状态,使不同类型单元的弹性模量缩减可按同一表达式进行,能克服现行评价方法中存在的问题,并可将弹性模量调整法扩展至所有类型钢岔管的极限分析和安全评价中。对某月牙肋岔管安全评价表明：基于弹性模量缩减法的钢岔管安全评价方法有良好的计算精度和计算效率; 现行基于应力分类的安全评价方法不能充分考虑钢材的塑性性能,计算耗材量较大; 按规范设计的月牙肋岔管的整体膜应力和月牙肋应力的强度储备较高,局部应力是引起结构破坏的薄弱环节。

英文摘要：

This paper points out the problem of the traditional safety evaluation method based on the elastic stress categories, i.e. the method is inconsistent with the plastic theory, and develops a method for evaluation of steel pipe bifurcation by using the elastic modulus reduction method （EMRM）. By the new method, different generalized yield criteria are adopted for different types of elements in the elastic iteration of suitable stress fields and an element-bearing ratio is used to represent the loading state of all the elements, so that the same equation of EMRM can be solved for various types of elements. This makes EMRM possible to apply to safety evaluation of all the steel pipe bifurcations. A case study of a crescent-rib reinforced steel bifurcation shows a good accuracy and efficiency. By this study, the traditional method produces in a conservative evaluation due to its neglect of material plastic nature, and results in higher margins of the membrane stress and crescent-rib stress safety as the local stress is the weakness of this type of bifurcation.