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Earthquakes and Structures
  Volume 8, Number 4, April 2015, pages 859-887

Operational modal analysis of a long-span suspension bridge under different earthquake events
Yi-Qing Ni, Feng-Liang Zhang, Yun-Xia Xia and Siu-Kui Au

    Structural health monitoring (SHM) has gained in popularity in recent years since it can assess the performance and condition of instrumented structures in real time and provide valuable information to the asset\'s manager and owner. Operational modal analysis plays an important role in SHM and it involves the determination of natural frequencies, damping ratios and mode shapes of a constructed structure based on measured dynamic data. This paper presents the operational modal analysis and seismic response characterization of the Tsing Ma Suspension Bridge of 2,160 m long subjected to different earthquake events. Three kinds of events, i.e., short-distance, middle-distance and long-distance earthquakes are taken into account. A fast Bayesian modal identification method is used to carry out the operational modal analysis. The modal properties of the bridge are identified and compared by use of the field monitoring data acquired before and after the earthquake for each type of the events. Research emphasis is given on identifying the predominant modes of the seismic responses in the deck during short-distance, middledistance and long- istance earthquakes, respectively, and characterizing the response pattern of various structural portions (deck, towers, main cables, etc.) under different types of earthquakes. Since the bridge is over 2,000 m long, the seismic wave would arrive at the tower/anchorage basements of the two side spans at different time instants. The behaviors of structural dynamic responses on the Tsing Yi side span and on the Ma Wan side span under each type of the earthquake events are compared. The results obtained from this study would be beneficial to the seismic design of future long-span bridges to be built around Hong Kong (e.g., the Hong Kong-Zhuhai-Macau Bridge).
Key Words
    long-span bridge; earthquake excitation; operational modal analysis; identification of predominant modes; structural condition assessment
Yi-Qing Ni, Feng-Liang Zhang, Yun-Xia Xia: Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong

Feng-Liang Zhang: Research Institute of Structural Engineering and Disaster Reduction, Tongji University, 1239 Siping Road, Shanghai, China

Siu-Kui Au: Institute for Risk and Uncertainty and Centre for Engineering Dynamics, University of Liverpool, The Quadrangle, Brownlow HillL69 3GH, United Kingdom

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