Research On The Free Vibration Frequency Measurement Of Bridge Based On High-speed Camera

Bridge plays an important role in the economy and daily life. The maintenance and protection of the bridge structure is becoming an important research direction. The bridge structure will be damaged with the increasing of vehicles load. The load and environment can seriously affect the safety and durability of the structure. Free vibration characteristics of the bridge structure can reflect the overall stiffness of the bridge structure. The modal parameters based on the free vibration characteristics can effectively identify the damage of bridge. It is therefore significant to explore a more convenient, intelligent method to test the free Vibration Characters of the Bridge.This paper analyzed the advantages and disadvantages of the commonly method used in bridge dynamic displacement. Based on the high-speed imaging technology, we proposed the further research on the measurement of bridge dynamic displacement. This measure combine with contemporary cutting-edge digital image processing technology. In the laboratory, the stability of the frequency of high-speed cameras can be tested by the interval between each of two pictures and the amount of time when shooted a certain number of pictures. The result showed that the errors in static experiment was 0.001 cm. O ne-dimensional motion of a cantilever structure had been carried by the high-speed camera. Take control of variable research methods, acquisition the image of the measuring point in Vibration. It got the value of the pixel in the coordinates by the method basing on image processing. Then calculating the coordinates of the amount of change, the value in terms of pixel was changed for the value in terms of the length dimension by a certain percentage. The first-order vibration frequency was obtained by FFT frequency domain analysis. In a suitable environment this method is convenient and high accuracy.This study choosed an urban bridge in Guangdong Province to test its engineering viable in examining the dynamic displacement of the bridge by the high-speed imaging technology. The data of Free Vibration C haracters of the Bridge was collected by DH5922 dynamic tester and image-based high-speed camera at the same time. The result revealed that the result of the dynamic tester was closed to the theoretical value, meanwhile the digital image method based on high-speed video camera can effectively identify the frequency and get the peak obviously. The fluctuating wind and other base vibration leaded to the gap in the testing result between engineering experience and image-based high-speed camera. The findings of digital image method also provide valuable insights into engineering application.