Application Of Fiber Bragg Grating Base Fixture Measurement Method In Cable Tension Monitoring

As the main component of the cable structure,the distribution and transmission of the internal force of the structure,the safety and stability of the whole structure will be shown on the cable force.Whether the cable force can be measured and monitored effectively is the key technology for the safe construction and normal operation of the cable structure.Light grating has advantages such as light weight,electromagnetic interference,corrosion resistance and wide monitoring range,according to the different structure form of cable structure,the placement method of fiber grating base fixture in vitro and the placement method of fiber grating base fixture are put forward for the bare cable and the sheathed cable.First,the structure of the two new cable force measuring devices and the principle of cable force measurement were introduced.Then through the global cable prestressed steel frame scale model test of fiber grating in vitro base fixture layout method,transverse comparison between fiber grating base fixture external placement method and pressure sensor method and resistance strain method was carried out to verify the reliability of fiber grating base fixture external placement method.Through the tensile and fatigue tests of fiber grating base fixture in vivo layout,the applicability of fiber grating base fixture internal layout method under different loads was tested,and the reliability of cable tension monitoring under long-term repeated load was verified.Finally,the fiber Bragg grating base fixture in vitro arrangement method was applied to the cable force monitoring of the tension construction stage of the cable curtain wall project in the Western Service Center of Kunshan,the reliability of fiber grating base fixture external placement method in actual engineering monitoring and the influence of temperature change and prestress loss on cable force were analyzed.The fiber grating was arranged in the base fixture method used in Lianyungang Longju engineering bridge sling tensioning construction stage cable force monitoring,the reliability of fiber Bragg grating base fixture in the actual engineering under various loads is analyzed,and the effect of prestress loss on cable force is analyzed.The main conclusions of this paper are as follows:(1)The measurement method of fiber Bragg grating base fixture is divided into fiber grating base fixture external placement method and fiber grating base clamp internal layout method according to the different structure form of cable structure.The two methods are clamps of FBG sensors and cables to be fixed in parallel.By measuring the strain between clamps,the real-time cable force of cables can be calculated.They are convenient and practical,and will not destroy the anticorrosion protection of cables.(2)Taking the arrangement of fiber Bragg gratings in the body as an example,combining the two physical parameters of effective metal section area and elastic modulus of cable,based on fiber grating sensing principle and Hooke's law,a theoretical formula for measuring cable force based on fiber grating base fixture internal layout method is obtained.(3)A cable structure scale model to simulate the cable force monitoring test of new engineering and existing engineering verifies that the fiber grating base fixture external placement method is suitable for the complex and changeable cable force measurement.At the same time,apply pre tension fiber Bragg grating to cable tension measurement.which can not only increase the cable force but also reduce the cable force.(4)The tensile and fatigue tests of steel wire bundles are carried out through the placement method of fiber Bragg grating base fixture,which proves that the method can accurately monitor the cable force variation of wire bundles,and showing good linearity and repeatability.(5)The cable curtain wall construction is usually constructed by phased tension,and the cable force after the end of each stage is affected by the double influence of the temperature and the loss of prestress,fiber grating fixture layout method can base in vitro caused by temperature change will change in quantity and amount of cable force separation caused by prestress loss from determine the tensile value of the last stage on the basis of prestress loss are measured,ensure the cable force reach the predetermined target value.(6)Tied arch bridge is usually used in stages of tensioning,the fiber grating is arranged in the method of actual cable separation caused by the loss of prestress force out variation,according to the measured data to determine the prestress loss of late super tension,to ensure that the final value reaches a predetermined target value of cable force.