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Wind and Structures
  Volume 10, Number 6, November 2007 , pages 555-576

Experimental study on possible vortex shedding in a suspension bridge. Part II – Results when under typhoon Babs and York
S. S. Law, Q. S. Yang and Y. L. Fang

    Statistical analysis on the measured responses of a suspension bridge deck (Law, et al. 2007) show that vibration response at the first torsional mode of the structure has a significant increase at and beyond the critical wind speed for vortex shedding as noted in the wind tunnel tests on a sectional model. This paper further analyzes the measured responses of the structure when under typhoon conditions for any possible vortex shedding events. Parameters related to the lifting force in such a possible event and the vibration amplitudes are estimated with a single-degree-of-freedom model of the system. The spatial correlation of vortex shedding along the bridge span is also investigated. Possible vortex shedding events are found at both the first torsional and second vertical modes with the root-mean-square amplitudes comparable to those predicted from wind tunnel tests. Small negative stiffness due to wind effects is observed in isolated events that last for a short duration, but the aerodynamic damping exhibits either positive or negative values when the vertical angle of wind incidence is beyond ?10o. Vibration of the bridge deck is highly correlated in the events at least in the middle one-third of the main span.
Key Words
    wind; typhoon; dynamic; vortex shedding; suspension bridge; steel; traffic; model; optimization.
S. S. Law; Civil and Structural Engineering Department, Hong Kong Polytechnic University, Hong Kong, People?s Republic of China.
Q. S. Yang; Bridge Engineering Department, Beijing Jiao Tung University, People?s Republic of China.
Y. L. Fang; Mechanical Engineering Department, Tai Yuen University, People?s Republic of China.

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