Wind and Structures

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Wind-induced self-excited vibrations of a twin-deck bridge and the effects of gap-width

  • Qin, X.R. (CLP Power Wind/Wave Tunnel Facility, The Hong Kong University of Science and Technology, Institute of Mechanical Design and Its Theory, School of Mechanical Engineering, Tongji University) ;
  • Kwok, K.C.S. (CLP Power Wind/Wave Tunnel Facility, The Hong Kong University of Science and Technology) ;
  • Fok, C.H. (CLP Power Wind/Wave Tunnel Facility, The Hong Kong University of Science and Technology) ;
  • Hitchcock, P.A. (CLP Power Wind/Wave Tunnel Facility, The Hong Kong University of Science and Technology) ;
  • Xu, Y.L. (Department of Civil and Structural Engineering, The Hong Kong Polytechnic University)
  • Received : 2006.03.29
  • Accepted : 2006.10.24
  • Published : 2007.10.25
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Abstract

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.

Keywords

References

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