一种基坑钢支撑预应力施加数值模拟方法研究

Numerical Simulation of Prestress Application to Steel Support of Foundation Pit

在FLAC3D中,采用梁单元模拟基坑钢支撑时,现有的预应力施加模拟方法是在梁单元设置以后,通过对梁单元两端的节点施加一对相反的作用力来代表要施加的预应力,导致支撑预应力变为围护体系的外力这一与实际不符的情况发生。为此,本文根据钢支撑与围护结构相互作用的机理,提出一种改进的钢支撑预应力施加模拟方法—虚拟位移法,即先固定梁单元一端节点,另一端节点施加节点虚拟位移,虚拟位移再施加于梁单元上,使梁单元压缩形成预应力。以深圳地铁5号线前海湾站基坑工程为背景,进行了常规方法和虚拟位移法的比较:在对支撑结构的影响上,常规方法引起各道支撑的轴力变化与实际存在明显的差别,而虚拟位移法则与实际一致。本文工作有实际意义。

In FLAC3D , a pair of contrary forces used as prestress are applied at the end nodes of beam element when steel support of foundation pit is simulated using beam element according to existing methods, which makes strut prestressing turn into external force of enclosure system, and this is quite different from that in actual situation. Thus, an improved simulating method, named virtual displacement, is proposed in this paper based on the mechanism of in- teraction between steel support and bracing structure. Firstly, one end of the beam element is fixed and on the other end a node rate is applied to form node virtual displacement, then the virtual displacement is applied on beam element to make it compressed and the prestress is formed. In this paper the routine method is compared with Virtual displace- ment method under the background of foundation pit project in the Qianhaiwan Station of Shenzhen Metro Line 5 ： a- bout the affection on the support structure, the axial force change of each support structure calculated by traditional method is obviously different from that under actual condition, but the result by virtual displacement method consist- ent with that in practice.