Research On Analysis Of Stresses And Critical Length Of Bonding Section In Prestressed Bolt

Prestressed bolt is an economical and efficient reinforcement technology.However,due to the complexity and diversity of the interaction between the bolt and soil,the bolt design theory and calculation method are faultiness currently.It is of great significance to study and stress distribution on the bonding section and optimize the length of the bolt to design a safe and economical bolt and ensure the reliability of the anchoring project.Based on the stress transfer method and the Mindlin’s displacement solution method,this paper carries out theoretical derivation,and studies the stress distribution of the bonding section with engineering examples,optimizes the bolt length design method,and finally verifies the rationality of the results through Flac 3D simulation.Based on the stress transfer method,the elastic-plastic theoretical space model is established.Theoretical analysis of the stress distribution of the bonding section in the elastic stage,plastic stage and slip stage is carried out.Then the theoretical analysis of the length of the bolt is carried out,and the load utilization factor is introduced to analyze the appropriate length of the bonding section.Based on the Mindlin’s displacement solution,the stress distribution of the bonding section is analyzed,and the calculation formula for the length of the bolt is derived,and the research is carried out in combination with engineering examples.A bolt model was established through Flac 3D,and the stress distribution law of the bonding section after tension was simulated and analyzed,and a reasonable value for the length of the bolt was obtained.The main results are as follows:The paper introduces the side mode resistance coefficient k and the parameterβ,and derives it through the stress transfer method,and obtains the axial force and shear stress distribution formulas of the bonding section in the elastic,elastic-plastic and slip stage respectively.The distribution of axial force and shear stress in the elastic phase is a hyperbolic function,the distribution of axial force and shear stress in the plastic phase is an exponential function,and the distribution of axial force and shear stress in the slip phase is an linear function.Assuming that z₁is the boundary point between the elastic zone and the plastic zone,the position of the boundary point z₁ is theoretically deduced,which is generally at the first 1/3 of the full length of the bonding section.A formula for calculating the length of the bolt is deduced,and finally the rationality of the result is verified by an engineering example.Using Mindlin’s displacement solution to derive the axial force and shear stress distribution formula of the bolt after tension,and analyze the stress change law,and then derive a different calculation method of the bolt length,and analyze the influence of the physical parameters of the soil.The shear stress has a stress concentration phenomenon,which is mainly concentrated in a small part of the beginning area of the bonding section.The higher the strength of the soil medium,the more concentrated the shear stress distribution.An engineering proposal for the design of bolt support is put forward:bolt support needs to reinforce the position of the beginning area of the bonding section and the bolt support is more efficient in soil with low elastic modulus.