正弦衰减荷载下锚杆支护粘结体塑性演化模型

Plastic evolution model of bonding in anchor bolt support under the sine attenuation loadings

针对锚杆与围岩之间的粘结单元,给出特定的正弦衰减循环荷载函数,引入损伤变量,推导出粘结单元累积塑性切应变随荷载循环次数的演化模型.在锚杆端部施加正弦衰减荷载,通过测量锚杆轴向不同深度轴向应力,计算粘结部位平均剪应力分布情况,并以此计算锚杆端部位移随荷载循环次数的变化规律,拟合出粘结体累积塑性演化模型中的具体参数.采用Ansys有限元分析软件模拟多个荷载周期下的锚杆位移值,并与理论值进行对比.研究表明:正弦衰减循环荷载下粘结体累积塑性切应变由初始荷载和振幅荷载累加产生,且加载频率只影响初始荷载产生的应变部分,试验结果拟合出的理论表达式与数值模拟结果基本一致,反映了粘结体切向累积塑性应变随循环次数先快后慢最终急剧增加的变化规律.

Mechanical properties of bonding effect between anchor and surrounding rock under cyclic loadings is an important factor that influences on the long-term safety and stability of anchor bolt support projects. In order to derive an evolution model of cumulative plastic shear strain increasing with loading cycle times, by setting the bonding element between anchor bolt and surrounding rock as research target, a specific sine attenuation loadings was given and damage variable was introduced. By measure the axial stresses, which was motivated by sine attenuation loadings applied at the end of the anchor, the mean shear stress distribution of bonding sites was calculated, which can be used for computing anchor head part’s displacement variation law with load cycles and fitting parameters in the cumulative plastic shear strain evolution model of the bonding element. Finite element analysis software Ansys was utilized to simulate the anchor’s displacement under numbers of loading cycles,which was eventually compared to the theoretical value. Studies have shown that only the shear strain generated by initial load was influenced by the frequency, and together with the loading amplitude, it made up the cumulative plastic shear strain of bonding element, which increased slowly after the first rapidly but eventually severely, according to the theoretical expressions fitted by experiment results and the numerical simulation.