Real-time Elevation Measurement And Damage Detection Of Cable-stayed Bridge Based On The Change Of The Cable Force

Cable-stayed bridge is one of the most commonly used bridge type especially for the medium and large span bridges because of its great spanning capacity, pretty shape, economy and practical features. The damage detection and health monitoring of cable-stayed bridges attack more attention in recent years owing to their important role in transport and economic activity. Cable is a significant component of the cable-stayed bridge, and the change of cable force is corresponding to the displacement of the connecting point between the cable and the main girder(called cable-girder anchor point), which controls the deck elevation of the bridge. In addition, cable contains a wealth of information about the parameters of main girder, it means that the damage of the main girder can lead to the change of the cable force. Based on the above principles, this paper studies the way to measure the real-time elevation of the bridge and the method to identify the damage of the main girder based on the change of the cable force. The main works of this paper are as follows:(1) The method to get the real-time cable force based on HHT transform is studied, and the accuracy of time-frequency curve obtained by HHT is verified by using the simulated signals of multi-frequency sinusoidal and single cable vibration, respectively. The real-time cable force curve can be obtained by the cable force calculation method based on vibration frequency. In addition, the influence of the upper and lower limits of filtering wave on the accuracy of time-frequency curve obtained by HHT transform in filtering process is studied in this paper, the best upper and lower limits to obtain the best results are suggested.(2) The change of cable force relates to the displacement of the cable-girder anchor point. First, the relationship between the vertical displacement of the cable-girder anchor point and the change of the cable force is deduced assuming the cables are in elastic state and the pylon is unlimited stiffness. And then the influence of horizontal displacement of the cable-pylon anchor point to the vertical displacement of cable-girder anchor point with the limited stiffness of pylon is analyzed, and the modified formula with considering the horizontal displacement of the cable-pylon anchor point is deduced. Numerical examples show that for the conventional cable-stayed bridge, the accuracy of the simplified formula is between 80% and 90%, and the accuracy of the modified formula can reach to 85%-100%. For the convenience of calculation in the engineering practise, the simplified formula is suggested to use.(3) A new method of measuring the real-time elevation of the cable-stayed bridge based on the change of cable force is proposed in this thesis. First, all cables' real-time cable force are obtained by HHT transform, and then the real-time elevation of the cable-girder anchor point are calclulated by using the simplied formula proposed above. Once all of the vertical displacement of the cable-girder anchor points are obtained, the real-time elevation of the bridge deck is fitted. The accuracy of this new real-time elevation mesearnment method is verified by using the measured results of Hedong bridge from the GPS and precision level.(4) Cable contains a wealth of information about the parameters of main girder, and the damage of the main girder will lead to the change of cable force nearby the damaged region. Based on this principle, using the variation of the cable force between the demaged state and the undamaged state as the objective function, a damage detection method of the main girder based on the cable force change is proposed based on idea of the model updating. Program is carried out by using the optimization design module of ANSYS. The numerical example shows that this method can identify both the single damage and multi-damage accurately.