The Study Of Nonlocal Friction Effect And Pullout Capacity Of Anchor Bolt (Cable)

The Coulomb's friction model is widely used in geotechnical engineering. In this model, frictional stress at a point on contact surface depends only on the normal stress acting on the point. In order to analyze the effect of contact surface to friction, a nonlocal friction model is introduced to analyze the mechanical characteristics for geomaterial. Roughly speaking, the nonlocal friction model is given to describe that impending motion at a contact point between two deformable bodies will occur when the shear stress at the contact point reaches a value proportional to a weighted measure of the normal stress in a neighborhood of the point.The nonlocal friction model proposed by Oden et al was modified in this dissertation. Anchor bolt (cable) are analyzed by using the modified nonlocal friction model. The influence of the kernel function in model is also studied. Based on gradient theory, the second-order gradient of stress is introduced into the nonlocal friction model. A gradient dependent nonlocal friction model is established and applied, the triple shear unified failure criterion which can reflect the intermediate principal stress effects on the yield characteristics and the nonlinear Mohr failure criterion are used to studied the ultimate pullout force of prestressed cable. The main content of the paper are summarized as follows:The modified nonlocal friction model is used to analyze the anchorage mechanism of the interior bond section of the prestressed cables. Based on Kelvin s solution of displacement, a solution of shear stress in the anchorage is derived. The integral form of shear stress is obtained and solved. The nonlocal effect on the contact surface is shown and the solution of shear stress is given. The results are compared with those obtained by the nonlocal frication model and local frication model. Factors affecting the nonlocal friction are discussed.Based on modified nonlocal friction model, the mechanical condition of the anchorage segment of the pressure-type cable is analyzed. The mechanical equilibrium equation is given and solved with the perturbation method. The nonlocal effect on the contact surface stress distribution is shown and the solution of shear stress and the axial force in a cable is given. The results are compared with those obtained by the nonlocal frication model and local frication model. The results also show that nonlocal effect changes with nonlocal effect size.The modified nonlocal frication model was used to analyze the wholly grouted anchor. Based on Mindlin s solution of displacement, an elastic solution of shear stress on bolt surface for wholly grouted anchor is derived. Wholly grouted anchor was analyzed by the modified nonlocal frication models which have different kernel functions, the nonlocal effect on the contact surface stress distribution was shown here and the solution of shear stress on bolt surface was given. The results were compared with those obtained by the modified nonlocal frication model which has different kernel functions and local frication model and experimental results in references. It is found that the results obtained by modified nonlocal frication model coincides reasonably well with experimental results, and coincides better than the local frication model. The result shows that nonlocal friction law is more practicable. The nonlocal friction effect is also discussed along with different kernel functions.Based on the gradient theory, a gradient dependent nonlocal friction model is established and used to analyze the wholly grouted bolt and the pressure-type cable. The mechanical characters of the wholly grouted bolt and the pressure-type cable are similar. When the nonlocal friction effects are considered, the shear stress peak value at the anchorage zone is smaller than those obtained by using the model not accunting for nonlocal effects.Based on the gradient dependent nonlocal friction model and the ultimate equilibrium principle, the ultimate pullout force of prestressed cable is studied. In order to consider the influence of the intermediate principal stress, the triple shear unified failure criterion was used to analyze the prestressed cable.The nonlinear Mohr failure criterion, such as the hyperbolic Mohr farlure criterion and two-parameter parabolic failure envelope, are used to analyze the ultimate pullout force. A comparative study was made of the results of different strength criterion.The study is helpful for understanding the friction mechanism in geotechnical problems. Meanwhile, the mechanics characteristics of the anchor bolt (cable) are studied. Based on different failure criterion, the ultimate pullout force of prestressed cable is studied.It can serves as good theoretical bases for the application and development of the anchorage techniques.