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Wind and Structures
  Volume 10, Number 5, September 2007 , pages 463-479

Wind-induced self-excited vibrations of a twin-deck bridge and the effects of gap-width
X.R. Qin, K.C.S. Kwok, C.H. Fok,P.A. Hitchcock and Y.L. Xu

    A series of wind tunnel sectional model dynamic tests of a twin-deck bridge were conducted at the CLP Power Wind/Wave Tunnel Facility (WWTF) of The Hong Kong University of Science and Technology (HKUST) to investigate the effects of gap-width on the self-excited vibrations and the dynamic and aerodynamic characteristics of the bridge. Five 2.9 m long models with different gap-widths were fabricated and suspended in the wind tunnel to simulate a two-degrees-of-freedom (2DOF) bridge dynamic system, free to vibrate in both vertical and torsional directions. The mass, vertical frequency, and the torsional-to-vertical frequency ratio of the 2DOF systems were fixed to emphasize the effects of gap-width. A free-vibration test methodology was employed and the Eigensystem Realization Algorithm (ERA) was utilized to extract the eight flutter derivatives and the modal parameters from the coupled free-decay responses. The results of the zero gap-width configuration were in reasonable agreement with the theoretical values for an ideal thin flat plate in smooth flow and the published results of models with similar cross-sections, thus validating the experimental and analytical techniques utilized in this study. The methodology was further verified by the comparison between the measured and predicted free-decay responses. A comparison of results for different gap-widths revealed that variations of the gap-width mainly affect the torsional damping property, and that the configurations with greater gap-widths show a higher torsional damping ratio and hence stronger aerodynamic stability of the bridge.
Key Words
    wind-induced vibration; flutter derivative; system identification; twin-deck bridge; wind tunnel dynamic test.
X.R. Qin; CLP Power Wind/Wave Tunnel Facility, The Hong Kong University of Science and Technology,
Clear Water Bay, Kowloon, Hong Kong, China
Institute of Mechanical Design and Its Theory, School of Mechanical Engineering, Tongji University, 1239 Si-Ping Road, Shanghai, 200092, China
K.C.S. Kwok, C.H. Fok and P.A. Hitchcock; CLP Power Wind/Wave Tunnel Facility, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China
Y.L. Xu; Department of Civil and Structural Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China

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