深基坑组合型钢支撑梁稳定性分析

深基坑组合型钢支撑由多根H型钢通过高强螺栓连接而成，支撑梁被横梁和立柱组成的门架近似等间距支承，实践表明支撑梁承载力常被高估。根据支撑体系实际受力情况简化问题，假定横梁和立柱组成的门架为弹性支座，将均布在横梁上的多根型钢简化为作用横梁跨中的单根型钢，利用位移连续条件，先推导出单根横梁时支撑梁在竖向平面内稳定性计算长度取相邻横梁间距所要求的最小横梁刚度，而后分析横梁数量和结构初始缺陷对横梁刚度要求的影响，并指出将支撑梁简化为单根型钢偏于安全，还探讨将弹性分析结果应用到弹塑性结构的方法。结合某深基坑工程实例，按横梁强度计算的支撑梁承载力和支撑梁轴力监测结果都小于按支撑梁截面计算的承载力，说明所用横梁刚度低于最小刚度要求，支撑梁承载力由横梁刚度控制；现有立柱抗侧刚度不及横梁刚度1/10，支撑梁在水平面内稳定计算长度应取支撑梁全长。

STABILITY ANALYSIS OF ASSEMBLY STEEL STRUTS IN DEEP EXCAVATION

Assembly steel strut system was applied to retain soil in deep excavation and combined multiple H steels jointed by high-strength bolts. The strut was usually supported by beams and columns at nearly the same interval. Practices showed that the strut capacity was always overestimated if the beam displacement was ignored. To simplify the question according to the actual mechanical condition, the beam and column were assumed to be springs and the strut was assumed to be a steel. A formula of the minimum beam stiffness for a single beam was provided based on the displacement continuous condition so that the calculation length of the strut in the horizontal plane equaled the interval of columns. Furthermore, the influence of factors such as the initial imperfection of structure, number of beams, distribution style of steel in the beam and steel elastic-plasticity on strut stability was discussed. With a deep excavation example, it was shown that the strut capacity based on the minimum beam stiffness and the monitor result were less than those based on material parameters. The capacity of the struts in this project was determined by the beam stiffness. The calculation length of strut in the horizontal plane should be the entire length of strut because the column stiffness was less than one-tenth of the beam stiffness.