“换铰法”定义及应用步骤刍议
Definition of “Rotation-Release Method” and Its Application Procedure

结构动力自由度是结构动力学教学环节中的重要概念之一，是指在任意时刻确定全部质量所在位置所需的独立几何参数数量。而“换铰法”是一种计算结构动力自由度的方法。根据换铰法现有定义，使换铰后的体系成为几何不变体系所需增加的最少链杆数，即为结构的动力自由度数。然而，该定义中关于“几何不变体系”的要求在某些情况下过于“严格”，超出结构动力学关于确定全部质量独立几何位置参数的要求。为此，本文提出关于“换铰法”的改进定义，并给出换铰法应用的建议步骤。本研究提出的“换铰法”及所建议的应用步骤简洁易懂，对学生结构力学基础要求较低，适合面向本科生的课程教学。
The degree of dynamic freedom is an important concept in the teaching of structural dynamics, which refers to the number of independent geometric parameters ascertaining the location of all masses at any time. The “rotation-release method” is one of the methods to ascertain the degree of dynamic freedom. According to the current definition of the rotation-release method, the value equals the least number of hinged rods required to transform the system after setting joints rotation-free to a geometrically stable system. However, this requirement concerning a “geometric stable system” may be overly strict under some circumstances, exceeding the requirement of ascertaining the independent location of all masses in structural dynamics. Given this, this study proposed an amended definition of “rotation-release method”, in companion with suggested application procedures. The amended definition of the “rotation-release method” and the suggested application procedure for analysis are easy to understand and have low requirements on students’ previous knowledge of structural mechanics, and are suitable for undergraduate teaching.