Nondestructive Detection Method Of Prestress Based On Tangential Stiffness Of Anchor Head

Prestressed anchorage can give full play to the strength and self-supporting capacity of the structure,and is effective and economical.It is widely used in the construction of slopes,bridges,foundation pits and other engineering works.The use of prestressed anchor cable has also increased rapidly year after year.The amount of stress in the anchors determines the anchoring quality of the prestressed structure,which is a key factor affecting the stability and safety of the prestressed structure.Although the construction quality requirements are continuously improved,the accidents of engineering failure and damage caused by prestress loss are still emerging endlessly.Prestress detection methods abundant but each has its own defects.Techniques of reverse drawing of prestress anchor damages the structure.Optical fiber bragg grating,sensor method needs to be embedded.Precision of elastic wave method remains to be improved.By and large,the contradiction of anchor prestress detection lies in the contradiction between the large-scale detection requirements and the applicability and economy of existing detection methods.Aiming at the contradiction between detection requirements and existing methods,this paper is based on the research and application of contact stiffness in the manufacturing field.Based on the force transmission characteristics of prestressed anchor head structure,the prestress is transformed into the measurement of contact stiffness between the anchor device and anchor plate.The identification of tangential stiffness by elastic wave is proposed in order to find a new non-destructive testing method for prestressed anchor cable.In order to achieve this long-term goal,this paper mainly conducts the following work:1.This paper introduces the historical development and application status of prestressed technique,expounds the types and mechanism of prestress loss,then analyzes the superiority of prestress under anchor head to represent anchorage force.By comparing the advantages and disadvantages of various detection methods,a nondestructive detection method based on tangential stiffness of anchor head is proposed.2.After anchor cable tension,the stress is transferred to the anchorage body by locking the anchor device and anchor plate,and the stress changes the characteristics of the contact interface of the anchor head.Based on Hertz contact theory and GW statistical contact model,the rough contact between anchor device and anchor plate under stress is simplified as an anchorage-contact model,and the relationship between stress and tangential stiffness of contact surface in elastic deformation scope is established.Under the same anchor parameters,the tangential stiffness increases with the increase of anchor prestress.3.The test platform of prestressed anchorage is built,and the tangential static load test is designed and carried out.The relationship between tangential stiffness and prestress is studied by applying load on anchor device with thin jack.The relationship between each parameter in the test is consistent with the theoretical derivation,which verifies the correctness and effectiveness of the theoretical model.The dynamic load test of tangential stiffness was carried out with elastic wave as the non-destructive testing medium.The results show that the accuracy of the prestress measured by the non-destructive method needs to be improved,and the modified formula of the tangential stiffness force measurement is proposed according to the test prestress range.The detection process of prestressed anchor cable nondestructive testing method based on the tangential stiffness of anchor head is proposed.