Nowadays, the analysis on internal force of structure is based on the hypothesis of plane system, but it can not solve the problem of stereoscopy.

现阶段在工程结构内力分析中，主要是基于平面体系的假设，并不能完全解决结构的空间性问题。

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This paper discusses the problem of the reduction of inertial force system of rigid body in plane motion .

讨论了平面运动刚体上惯性力系的简化问题；

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