Study On Vibration Theory And Cable Force Test Of Grouted And Prestressed Cable

70-90s in the last century, traffic infrastructure construction developed rapidly in our country. Much many suspender-arch bridges and cable-stayed bridges were built during that period. At that time, the anti-corrosion structure of most suspenders was wrapped with outer tube and grouting cement mortar inside. Due to the presence of tube and grouting cement mortar, Large errors would be produced if we use existing vibration methods to test and calculate cable force. With the advance in technology of external prestressed cable, grouting external tendons has been more widely used in the newly built bridges and the existing bridges with external prestressing tendon reinforcement, which put forward new demands and challenges for cable tension testing of such cables.In order to use vibration frequency method to test the force of grouting cable force accurately, this paper conducted in-depth research and made a lot of grouting prestressed cable model. The main work and conclusions are as follows:1、The axial tensile beam hinged at both ends with additional uniform elastic mass to simulate the grouting cable. Vibration differential equation is derived, and the vibration mode function was obtained by solving the equation. The cable force formula was derived under the boundary conditions of hinged at both ends, and the interrelation of the measured vibration frequency and the calculate one, vibration frequency of the corresponding bare cable and the one of added elastic mass is obtained.2、To analyze the influence regularity on tension calculation of boundary conditions, additional mass and the various parameters of grouting cable,φ 15.2mm high strength steel strands are adopted to simulate the cables and we made 24 bare prestressed cable test models,24 prestressed cable test models with outer pvc tube but no grouting inside, then 24 grouting cable test models were also made, with the external prestressed cables of Hongtang bridge and suspenders of arch-bridge as the engineering background. The results showed that:hinged boundary conditions meets requirements of cable force in calculation; the added mass of outer tube should be taken into account when calculate cable force; use the existing cable force formulas to calculate the grouting cable force will produce large errors.3、Computation expression for the mortar’s vibration frequency was fitted by the parameters of cable length, grouting rate, linear density of the added mass, slenderness ratio, and the sectional flexural stiffness of mortar after the regression analysis on the test data. Then, the linear relation between the calculated frequency and the measured one was obtained. Finally, force calculation process of the grouted cable was summarized.4、1:1 prototype testing of grouting external cable for Hongtang bridge was made to verify the applicability of the theory and process of grouting cable calculation proposed. And the formula was used in cable force assessment of the external grouting cables in Fujian Hongtang Bridge and the suspenders of Mulan Brook Bridge in Xianyou, It is gratifying that a satisfactory result was obtained.