内支撑平面杆系有限元计算是基坑支护结构设计不可或缺的一环,其中边界条件的选择尤为重要。为解决目前基坑内支撑平面杆系有限元计算中边界设置不合理的现状,引入仅受压法向弹簧与切向弹簧形成组合弹性边界,采用有限元方法对基坑内支撑平面计算进行分析,探讨了弹簧刚度系数对内支撑受力和变形的影响。研究结果表明:仅受压法向弹簧与切向弹簧很好地消除了传统约束对内支撑受力与变形的影响,不仅可得到准确的内支撑水平等效刚度,而且可精确计算各杆件内力;内支撑受力与仅受压法向弹簧和切向弹簧刚度系数无关;相比仅受压法向弹簧来说,切向弹簧对内支撑位移起控制作用。该组合弹性边界物理意义明确,弹簧刚度系数取值容易,可在基坑支护设计中推广应用。

Finite element calculation of plane bar support system is an indispensable part of the design of foundation pit support, and the selection of boundary condition is especially important. To address the issue of unreasonable boundary setting in the finite element calculation of plane bar support system in foundation pit, a combined elastic boundary involving normal spring only subjected to compression and tangential spring is proposed in this article to investigate the influence of spring stiffness coefficient on the inner support force and deformation of foundation pit in finite element analysis. Results showed that by eliminating the influence of traditional constraints on the inner support force and deformation, the combined elastic boundary could result in a more accurate horizontal equivalent stiffness of inner support, and more precise internal forces. The inner support force has no concern with the stiffness coefficient of the normal spring only subjected to compression and the tangential spring. In addition, the displacement of inner support is controlled by the tangential spring rather than by the normal spring only subjected to compression. The proposed combined elastic boundary has clear physical meaning, and the value of spring stiffness coefficient is easy to obtain, hence could be applied to the design of foundation pit support.