Cable Force Identification Based On Non-contact Photogrammetry System

Cable is the main power-transmission component of cable bridge structure, which plays a key role in bridge safety. C able force is an important indicator of stayed cable's condition state. Therefore, it is necessary to monitor the cable force. Vibration-based cable force estimation has been widely used in engineering because of its characteristics of convenience, rapidit y and repeatablity. However, under certain conditions, they are facing the deficiencies of slowness in installation, relatively complicated work, environmental limitations, high cost and unable to consider the boundary conditions. To solve these problems, the paper proposes the method of identifying the cable force based on the photogrammetry and mode shapes. The main contents are shown as follows:(1) This paper presents the estimations of tension force of a cable using the moving target image tracking technologies. A video camera is employed to capture the vibration image sequences of single or multiple targets installed along the cable. The background difference method is used to detect the moving targets, and then the Kalman filter is conducted to track the moving target, from which the vibration response of the cable can be attained to extract the cable force via general frequency-based method. The experimental test results reveal that there is a small error between the results measured from photogrammet ry and those from accelerometers. The photogrammetry method has the potential of becoming the effective complement of the non-contact testing.(2) The paper studies the measurement method of cable vibration displacement which is based on photogrammetry. As a frame of reference with the camera calibration board, utillizing the plane of camera imaging and the correspondence of point's coordinates according to the calibration board in order to build camera model.Thus it's able to establish the corresponding re lationship between 2D image and 3D entities, and solve the camera's internal and external parameters. After calibrating camera, it can decuce the acual displacement from the object's image displacement.(3) The paper finds the complicated boundary conditio ns' estimation of cable force based on the cable vibration mode. It regards the stagnation of cable segment as an ends-hinged equivalent model through the modal test to find out two modes of cable adjacent supporting point. The paper calculates the equival ent cable force according to the relationship of cable force- frequency from the equivalent model, and approximates the equivalent cable force as the original one. What's more, it preliminary verifies the equivalent cable force's accuracy and feasibility via ANSYS method and laboratory simulation.