Research On Detection And Identification Of Effective Prestress Of Post-tensioned Prestressed Concrete Beams

Effective prestress in prestressed concrete structures is an important indicator of the working state of the structure.Whether the effective prestress of the beam can be accurately determined is related to the safety and usability of the structure.Once the prestress loss is too large,the structure will be at risk for safety accidents.It can be seen that only when the effective prestress value is accurately measured can it provide a reliable basis for the use and maintenance of the post-tensioned prestressed beam.For this reason,the research on the effective prestress detection method under the anchor after construction and the effective prestress identification method on the bridge after operation have important engineering application prospects.Based on a review of domestic and foreign literature,this article studies the reverse tension method commonly used for effective prestress detection methods under anchors,and the concrete stress release method for effective prestress detection and identification in beams.Based on the comparative experimental study of the back-pulling method,based on data analysis and processing,we seek to find a correction method to improve the accuracy of data processing.Through ANSYS simulation modeling and calculation analysis of prestressed concrete simply-supported beams and continuous beams,the research must be carried out.Under the condition of the groove,the depth of the zero-point stress release is affected by the loading load,so as to improve the implementability of the concrete stress release method.The main research contents and conclusions of this article are as follows:(1)This paper summarizes the prestress detection methods under the anchor,the effective prestress detection methods and related theories of the beam body,and systematically analyzes the factors affecting the prestress loss during the tensioning and anchoring stage,the factors affecting the prestress detection,and the current status of research and application.(2)Combined with the reverse tension method to detect the prestress test data under the anchor for comparative analysis,the law of the test system error is found by comparing with the test value of the load cell.According to their correlation,the slopes of the two curves in the test control section are close to each other and the displacement difference starting from this relationship that is basically fixed,a basic method for correcting the test data of the inverse pull method is proposed.After the correction,the test error is greatly reduced and the test accuracy is significantly improved.Through typical verification tests,the reliability of the correction method is verified.It provides a feasible idea for the correction of the test data of the inverse pull method.(3)The finite element software ANSYS was used to model and simulate the prestressed simply supported beams.The sub-model analysis method was used to simulate and calculate the local stress release process.By comparing with the existing research results,the correctness of the model and slotting method in this paper was verified.It is proved that the zero-point stress release depth h/d of the structure is 0.3?0.35.Through the concentrated loading of two points of the model,the load size is increased step by step,and the influence of the loading process on the stress release process and release depth is studied.The simulation results show that when the concentrated load gradually increases to 950 k N,h/d gradually approaches from 0.35 to 0.3;when the concentrated load is between 950 k N and 1 390 k N,h/d remains between 0.25 and 0.3,and gradually approaches 0.25 as the load increases.,Indicating that the zero-point stress release depth gradually decreases with increasing load.(4)The same modeling method as that of the simply supported beam is used to model and analyze the prestressed concrete continuous beam,and the stress release process is simulated.The calculation results under the two-point loading mode in which the joint is concentrated in the midspan and span show that when the concentrated load is less than 1300 k N That is,when the prestress degree ? is greater than 4.55,h/d is always between 0.3 and 0.35,and with the increase of the load(? gradually increases),h/d gradually approaches from 0.35 to 0.3;when the concentrated load is 1 300 k N?1 804.255 k N When ? is less than 4.55,h/d is always between 0.25 and 0.3,and with the increase of the load(? gradually decreases),h/d gradually approaches from 0.3 to 0.25.It can be seen that the stress release process and its law and the simply supported beams are basically the same,and it is also found that the depth of the zero-point stress release can be reduced after the joint loading to a certain value.