Study On Auto-measuring Technology For Cable Tension Of Stayed-Bridge Based On Frequency Method

Cable is the main component, which supports the gravitation of the cable-stayed bridge. Cable tension is an important parameter to estimate the bridges' health condition. The Random Excitation Vibration-frequency Method is the most economical and frequently used method for cable tension monitoring, because it is not necessary to install sensor during construction and the measurement can be done without interrupting traffic. The current problem of Random Excitation Vibration-frequency Method is that: it is very difficult to get the natural frequency of cable vibration without high-accuracy sensor and manual intervention due to strong and complicated noise accompany with the useful vibration signal. To meet the needs of long time and on line bridge structural health monitoring, appropriate sensors and intelligent software are needed to automatically collect and analyze the vibration signal and identify the natural frequency of cable, and then calculate the cable tension. Therefore there is plenty of work to do in the intelligent software development and comparative study of sensors.The main work of this thesis includes:â‘ Existing problems were revealed by analyzing current researches on cable tension measuring methods and put forward key points in this dissertation.â‘¡The relation between cable tension and its vibration frequency was deduced, and many factors which infect cable tension and vibration were considered and amended, and the cable length calculation method was given. Practical cable tension calculation equations were given based on above analysis.â‘¢An experiment setup was settled to do comparative study of different sensors, and low frequency capability of LC0116, GT02 and 941B acceleration sensor were tested. The vibration mode of cable was studied, and sensor installation position was discussed based on the vibration mode. The influences of signal acquisition (A/D) frequency and duration on cable tension measurement accuracy were discussed. Software, which has both difference frequency and iteration natural frequency identification method, was developed.â‘£A practical cable tension measurement system were developed and implemented on Chongqing Cai Yuanba Yangtze River Bridge. The system was calibrated on-the-spot during the stretching process of short suspension cables on the bridge. The feasibility of our automatic online cable tension monitoring system was then demonstrated.