Modal Parameter Identification for the Cables and Body of the Cable-Stayed Bridge by the Way of Multiple Random Decrement Method with Dates of Cable Ambient Vibration Measurement

• Main Authors: Jau-an Liau, 廖釗銨
• Other Authors: Wen-Hwa Wu
• Format: Others
• Language: zh-TW
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/39471809419002820718

碩士 === 國立雲林科技大學 === 營建工程系碩士班 === 95 === The bridge cable is the primary member which transmits the strength in cable-stayed bridge overall construction system, so it can reflect the dynamic performance and the healthy condition of the overall bridge system directly. At the same time, the cable’s geometry shape can regard as the pure dimensional structure which makes it relatively simple to carry the measurement and analysis of the dynamic response on. Therefore ambient vibration measurement and following dynamic parameter identification of cable are the best shortcut to carry on the health monitor to the whole cable-stayed bridge. But the dynamic response of the bridge cable which occupies by higher frequencies occupies the composition proportion is high because of lower lateral-stiffness, we usually must distinguish the more model parameters above. The ways about the system-identification of the cable-stayed bridge most carry on the ambient vibration measurement by the mobile and simple establishment in the last few years. We must apply the system-identification skill which is only according to the output signals to decide the model parameters, because the ambient vibration measurement of the bridge cable only can obtain the output signals. And we don’t easily carry on the multi-spot even distributive measurement for the identical cable because of field work limit. In addition, the signals of the ambient vibration measurement are usually minimum. The questions of signals often create the puzzle in the practice application such as noises and so on. We carry on the preliminary analysis through the ambient vibration measurement record of cables of the Chi-Lu cable-stayed bridge. The paper inspires the frequency of every cable respectively first; moreover, the conspicuous model frequencies of the bridge body are pointed out by the overlapping and compared way. Before developing the new method, we first aim at the tradition random decrement method and Ibrahim time domain identification to conduct the detailed parameter research. Above these foundations, the most important achievement of this research is to combine the innovative mode parameters with multiple random decrement method to develop the effective method distinguishing multiple mode parameters of cables by using ambient vibration measurements from single station. This set of method fully uses the dynamic performance of bridge cable. On the one hand, it improves many complex questions about distinguishing multiple mode parameters simultaneously to decide mode parameters separately by way of the mode separation. Meanwhile, it filters thoroughly influence of the external force’s noise and the bridge body’s mode frequencies and so on to compute mode damping ratios accurately by way of the multiple random decrement method. Taking the dates of the Chi-Lu cable-stayed bridge cables’ speed ambient vibration measurement as an example, its identification result clearly confirms this method sufficiently provides the precise identification to the multiple mode parameters of bridge cables.