Abstract
The damping ratio and frequency of vertically vibrating bridge deck section models under zero wind speed, extracted by the proposed piecewise fitting method from both vibration tests and fluid-structure interaction simulations, vary exponentially with vibration amplitude. In vibration tests, the damping ratio of a tri-box section model will be doubled when the top and/or bottom of the two gaps between the three boxes are covered by grilles. Air-induced damping is firstly identified as an important source of damping of a section model. The air-added mass also has a notable influence on the vibration frequency of section models. For three section models with shapes of tri-box, grille-covered tri-box, and closed single-box, the amplitude-averaged air damping ratios account for 48.5%, 67.5% and 55.1% of the total damping ratios of vibrating systems, respectively; and the amplitude-averaged added masses account for 3.8%, 4.3% and 12.8% of the model masses, respectively. Explanations for the dramatically different air damping and added masses of the section models are given based on the flow patterns of the surrounding air. A dynamic equation including nonlinear air damping and added mass is presented to accurately reproduce the whole procedure of vibration tests.
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