The Studies On Cable Tension Of Cable-stayed Bridge Based On Vibration Monitoring

Stay cable is one of the main components in cable-stayed bridges. The magnitude, variation and distributing of the cable tension closely relate to the structural state of the bridge. Thus it is significant to measure or monitor the cable tension precisely. At present, the vibration-based method, i.e. frequency method, is widely used to measure the cable tension. However, the measured values of the cable tesion commonly deviate from the actual ones due to the theoretical simplication of the frequency method. The main objectives of the dissertation include: 1) to investigate the effects of the exication, the cable sag, and the boundary conditions on the measured frequencies; 2) to improve the precision of the cable tesion with the measured frequencies. In this study, the theoretical analysis and experimental simulations are carried out, which can be summarized as:(1) The mechanical characteristics of the stay cable is briefly analyzed. The existing methods of the cable tesion measurement are reviewed, and the research demends of the theory and applications on the cable tension measurement are proposed.(2) The theory of the frequency method is studied firstly. The in-plane and out-plane frequencies of the cable are analyzed under the different cable tension, sag, and boundary conditions etc. Then the theoretical relationship between the natural frequencies and cable tesions are derived.(3) Two paramenters , i.e.ζandλ~2 are adopted to define the bending stiffness and sag of the cable. The nonlinear property of the natural frequencies is verified by the model test. The effects of the cable sag, as well as the excitation pattern, sensor position, and the sampling rate, on the measured frequencies are investigated in the model test. The relationship between the natural frequencies and cable tesions are analyzed with the experiemental data.(4) For different cables, the feasibility of the existing methods to identify the cable tension are further studied with the measured frequencied. According to the therotical and experimental study, the calculation formulas for cable tension are proposed in the dissertation.(5) The proposed method are applied to Shengli Yellow River Cable-stayed Bridge. The identified cable tensions provide the data to assess the structural state of the bridge.