Abstract
On the preliminary designing of a wide flat box girder with the slenderness ratio 12, vertical and torsional vortex-induced vibrations (VIV) are observed in wind tunnel tests. More than one lock-in region, which are defined as“multi-lock-in regions,”are recorded. Therefore, suspicions should be aroused regarding the viewpoint that wide box girders are aerodynamic friendly. As the three nascent vortexes originating at the pedestrian guardrails and inspection rails shed to near-wake through different pathways with different frequencies, the mechanisms of VIVs and multi-lock-in regions are analyzed to be determined by the inappropriate subsidiary structures. A hybrid method combiningLarge Eddy Simulation(LES) with experimental results is introduced to study the flow-structure interactions (FSI) when undergoing VIVs; the vortex mode of torsional VIV on wide flat box girders is defined as “4/2S,” which is different from any other known ones. Based on the mechanism of VIV, a new approach by increasing ventilation rate of the pedestrian guardrails is proved to be effective in suppressing vertical and torsional VIVs, and it is more feasible than other control schemes. Then, the control mechanisms are deeper investigated by analyzing the evolution of vortex mode and FSI using Hybrid-LES method.
Highlights
Three Gorges Area has been playing decisive roles in southwest China and witnessing rapid developments in bridge constructions
According to the testing results, no Vortex-induced vibration (VIV) is observed in case of the bare deck, no matter the attack angle is 0∘, ±3∘, or ±5∘
Concerning the preliminary designed completed deck, there are no VIVs occurring at attack angles 0∘, −3∘, and −5∘
Summary
Three Gorges Area has been playing decisive roles in southwest China and witnessing rapid developments in bridge constructions. Several researches mentioned the effects of deck details on aerodynamic performance of bridges [10, 11], but they did not focus on wide flat box girders and provide little knowledge about the influence mechanisms. In the case that the maximum VIV amplitude of the designed bridge deck exceeds the allowable value, additional appendages, such as deflectors, suppression boards, and external dampers, are attached to the basic deck to change the flow field so as to avoid or suppress VIV [1, 5]. The organization is as follows: in Section 2, the backgrounds of a wide flat box girder are described and wind tunnel tests are carried out to determine whether the preliminary designed bridge deck undergoes VIV or not.
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