Study For Cable Tension Measurement Of Tonghua Xiuzheng Cable-Stayed Bridge

The stayed cable, as a kind of tension component, can bear 50% loads of its material ultimate bearing capacity. The steel wires in stayed cable are designed to bear periodical tension stress and not bending stress, and the bending stress will obviously reduce the anticipate fatigue life of steel wires. After the vibration of cable attains a certain number of times, the steel wire of the anchorage zone will rapture because of fatigue and damage. Therefore, large-amplitude resonance caused by wind and rain flaps will affect integrity, usage and durability, and also affect the safety of the structure. However as a fact of corrosion of the stayed cable, the structure condition of part cable-stayed bridge which built in early days is seriously damaged. Especially the stayed cable, because of corrosion, its using quality decayed early. The stayed cable is the main stress components, and if a certain cable split suddenly, it may cause disaster damage to the structure.Cable-stayed bridge belongs to higher order statically indeterminate structure, the magnitude of cable force affects structure performance very greatly, the stayed cable is similar to prestressed structure, and the cable tension force is usually confirmed after several times tension in the process of construction. Because of the limits of quantity of construction equipments and other condition, the tension can only carry on by grouping. The tension of cable and the magnitude of cable force affect performance of the whole bridge very greatly. Therefore, cable force is a core factor which affects the performance of cable-stayed bridge. It not only affects the rationality of the whole bridge, but also affects the flatness of the bridge and line type of the girder, and the comfort and the safety of driving. Successful implement of the bridge construction and comfort and safety driving during the service life, life of bridge, and the service term are all directly related with the magnitude of the cable force. The work appearance of the stayed cable is an important mark to measure whether the cable-stayed bridge under normal operation condition or not.So right and precise measure of the cable force causes more and more attention gradually, is one of the most important works in construction and run management of cable-stayed bridgeUp to the present, the methods can measure the cable force on the spot are mainly:(1)pressure gauge determination;(2)pressure sensors determination;(3)frequency method;(4)magnetic flux method;(5) vibrating wave method. In these mentioned methods, currently only the preceding three get an extensive application on the spot. Among them, the pressure gauge determination method is only applicable to test the force of tensioning cable, and difficult to measure the tensioned cable. Manometer test method has a higher accuracy, and is suitable to test the tensioning cable. Although this method can also be used to test the tensioned cable, in consideration of economic reason, generally not be adopted. The frequency method not only has a lot of advantages, such as: the test instrument becoming smaller gradually, convenient for taking, easy installation and can be used repeat, and its test accuracy is high, so the frequency method becomes the best choice of cable force test currently. The accuracy of cable force test has mainly two influence factors, which are:(1)Accuracy of the natural frequencyGenerally speaking, the data collected are dynamic time-history response curve on the end of cable by ambient excitation, the way used to extract the natural frequency of the cable from dynamic time-history response curve, and the accuracy of the extracted natural frequency all will affect the accuracy of the identified cable force.(2)Accuracy of the calculation model of cable forceThe influence of inclination of cable, bending stiffness of cable, shock absorber system, and temperature all will cause the change of cable force, whether the calculation model of cable force has considered those factors properly will affect the accuracy of cable force identification. Aiming at the situation mentioned above, this paper are mainly do research about:(1)At first, analyzes the influence factors of the accuracy of measured cable force, adopts the model of tensile horizontal straight beam with two pivoting ends to modify the sectional flexural stiffness ,and then derives caculation formula.Establish cable force calculation model by modified sectional flexural stiffness combined with the model of tensile horizontal straight beam with two fixed ends.(2)Introduces the solving theory and method of eliminating the tendency item, fourier transform, anti-aliasing filtering, windowing signal, digital filter designing and self-power spectrum,forms the extracting method of the natural frequency of stayed cable, and edits the natural frequency extracting program.(3)Measures the stayed cables of Xiuzheng bridge in Tonghua city by vibration test, then identifies the natural frequency of the stayed cable by modal analysis theory, at last, calculates the cable force adopted the model of tensile horizontal straight beam with two pivoting ends and the model put forward by this paper.