基于统计损伤理论的锚杆受力全历程分析

Analysis of the whole course for the force transferring mechanism in anchor bar based on statistical damage constitutive theory

基于统计损伤理论,假设锚杆剪切滑移界面各微元的剪切强度服从Weibull概率分布,建立了考虑残余强度的锚杆界面统计损伤本构模型,并选取微元建立锚杆锚固端的受力平衡,确立了锚杆各锚固深度下剪切滑移、轴力、侧阻力以及损伤的数值解法。基于室内拉拔试验确定本构方程,以工程实例进行了验证。同时对锚杆拉拔荷载传递的全历程进行探讨。结果表明:随着拉拔荷载的增加,锚杆顶部的侧阻力增长至峰值点后衰减,最终稳定至残余强度,剪应力分布单峰曲线进一步向锚固深度内传递,锚杆界面应力软化的本质是损伤积累并传递的过程。参数m能够反映剪切滑移曲线的峰后软化速率,减小m可以降低接触面软化和损伤积累传递的速率,从而降低锚杆整体刚度的退化速度,在一定荷载范围内减少锚杆滑移。

Based on the constitutive theory of statistical damage and the assumption that the shear strength of anchor bar's interface element obeys the Weibull probability distribution,a statistical damage constitutive model considering the residual strength for anchor bar's interface was established.A small segment of the anchor bar was selected to analyze the force balance,and then,the numerical solution of the shear slip,axial force,side resistance and damage of anchor bar was obtained.Based on an indoor pullout test,the constitutive equation was determined and verified by an engineering example.At the same time,the whole working course for the force transferring of anchor bar was studied as well.Results indicate that with the pulling force increases,the side resistance at the top of anchor bar increases to a peak value and then decays.Finally,it reaches the residual strength remaining unchanged and the shear stress distribution curve is further transferred to the deeper.The essence of the interfacial stress softening is the process of damage's accumulation and transferring.The parameter m can reflect the softening velocity of shear strength afterpeak value.Thus,decreasing the value of m can reduce the rate of stress softening as well as damage accumulation and transmission,thereby reducing the degradation rate of the overall stiffness of anchor bar and the anchor bar's displacement in a certain load range.