小型钢框架劲性水泥土挡墙的复合刚度研究

Study on complex stiffness of small steel frame rigid cement-soil retaining wall

小型钢框架劲性水泥土挡墙在荷载作用下的工作机理尚未明确,且基坑工程涉及较多不确定因素,需要进行可靠度分析。开展集中荷载作用下悬臂梁试验,分析试件的荷载-型钢应力曲线、荷载-挠度曲线,确定试件的复合刚度代表点,考虑物理、几何、静力平衡三方面条件对代表点进行综合分析,提出试件的复合刚度计算方法。再结合实例,基于MATLAB进行刚度和稳定性方面的可靠度分析,利用蒙特卡洛法、JC法和窄界法等计算其在不同失效模式下的失效概率和系统失效概率。结果表明:1)复合刚度理论计算值与实测值相差14.29%;2)可靠度分析发现,倾覆破坏和顶部位移过大的失效概率较大,体系蒙特卡洛法所计算失效概率处于窄界法所计算失效概率范围内。提出的复合刚度计算方法能够为该支护结构刚度的可靠度分析提供依据,倾覆破坏和顶部位移过大是其主要失效模式。研究成果对于小型钢框架劲性水泥土挡墙的设计和应用具有一定的指导意义。

The soil mixing wall（ SMW） is a supporting structure of foundation pit to provide major structural bearing capacity,composing of cement-soil and large steel. In traditional SMW,the contribution of cement-soil is neglected by design methods and the cost of large steel column is expensive. Therefore the small steel frame rigid cement-soil retaining wall has been explored to replace individual large steel columns in the SMW with small steel frames,and correlational researches have developed extensively. However,the working mechanism of small steel frame rigid cementsoil retaining wall under loads was unclear in the past decades. In addition,the foundation pit engineering includes various uncertainties,so the reliability analysis on the supporting structure is also in great urgent. In this study,experiments regarding cantilever beam under concentrated loads were firstly carried out and load-steel stress curve as well as load-deformation curve of specimen were analyzed. Secondly,based on the representative points of specimen composite stiffness,a new calculation method of composite stiffness on the supporting structure was proposed from aspects of physics,geometry as well as statics balance. Thirdly,the reliability analysis on stiffness and stability was implemented to calculate the systematic failure probability by using Monte-Carlo method,JC method,and narrow boundary method by MATLAB. The results showed that the calculated composite stiffness value of 14.29% was lower than the measured one. Besides,the results of the reliability analysis showed that there was considerable failure probability of overturning and excessive displacement on the specimen top. The failure probability calculated by systematic Monte-Carlo method was within the range of narrow bound method. Moreover,the calculation method of composite stiffness can be employed to execute the reliability analysis of supporting structure stiffness and to prove that overturning and excessive displacements of the top are the main failure modes. In conclusion,the results of this study can be utilized to make positive contributions to the design and application of small steel frame rigid cement-soil retaining wall.