The Cause Analysis And Correction Method Of Cable Length Error Of Cable-stayed Bridge And Its Construction Control Application

With the rapid development of super long-span cable-stayed bridges and the improvement of construction accuracy requirements,the length of cable needed to match has increased significantly.In addition,parallel steel wire cables are generally used in long-span cable-stayed bridges in China.The length of such cables cannot be changed after being made,so that higher cable length accuracy control requirements are required.In the past,the cable length error of cable-stayed bridge is common,if the error is too large,it will affect the normal anchorage of cable-stayed bridge.There are many reasons for the error of cable length,which runs through the whole process from the calculation of cable tension control force and unstressed cable length to the completion of cable anchoring at the construction site.In this paper,based on the actual project,the influencing factors of the length error of parallel steel cable are analyzed and studied,and the corresponding error correction method is proposed.The feasibility of the correction method is verified by the engineering application results,which also provides experience and reference for the future cable-stayed bridge construction.The main contents and conclusions of this paper are as follows:(1)The analysis shows that the accurate calculation of the tension control force and the unstressed cable length is the necessary condition for the smooth construction of the cable,the key to the smooth installation of the cable is to control and correct the cable length error,and the excessive cable length error will seriously affect the installation of the cable.Due to the contingency of the cable length error,the cable can not be tensioned completely according to the original theoretical data during the construction of the stay cable,otherwise it is very easy to have the situation that the anchor cup at the tensioning end of the stay cable can not be anchored because the stay cable is too long and the base plate is added or the stay cable is too short.The purpose of this method is to analyze the error of cable length in advance and adopt corresponding correction measures,so as to ensure that the cable can be anchored normally after tensioning.(2)In the whole process from the calculation of stay cable to the installation,the causes of cable length error are analyzed step by step.The new unstressed cable length value can be calculated by changing the corresponding calculation model parameters after considering the characteristics of each influencing factor.Then compared with the unstressed cable length value in the original model,the specific influence of each influencing factor on the cable length error can be obtained.The analysis shows that there are many factors that affect the cable length error,and some factors that are easy to be ignored may also have a greater impact on the cable length.In the process of calculation,manufacture and installation of stay cables,there will be uncertain factors that cause cable length error,that is to say,no influencing factors can be ignored in the actual construction control.(3)This paper presents a method to modify the cable length error control index with the exposed value of the cable anchor cup(the length of the anchor cup beyond the nut).This method considers the influence of cable force test,elastic modulus,temperature effect and anchor point coordinate on cable length from the perspective of construction control.The purpose of cable length error correction is achieved by adjusting the manufacturing length of cable and the position of anchor end nut in advance.The application results in Jiayu Yangtze River Bridge show that the method can improve the coincidence between the actual exposed value and the theoretical value of the cable after the completion of the cable tensioning,make the nut located in the effective thread area of the anchor cup,and ensure the efficient implementation of the cable installation process in the cantilever erection process of the main beam of the bridge.