• Wind and Structures
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• 제21권2호
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• pp.223-239
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• 2015

Open decks are a widely used deck configuration in long-span cable-stayed bridges; however, incorporating aerodynamic countermeasures are advisable to achieve better aerodynamic performance than a bluff body deck alone. A sectional model of an open deck cable-stayed bridge with a main span of 400 m was selected to conduct a series of wind tunnel tests. The influences of five practical aerodynamic countermeasures on flutter and vortex-induced vibration (VIV) performance were investigated and are presented in this paper. The results show that an aerodynamic shape selection procedure can be used to evaluate the flutter stability of decks with respect to different terrain types and structural parameters. In addition, the VIV performance of $\prod$-shaped girders for driving comfortableness and safety requirements were evaluated. Among these aerodynamic countermeasures, apron boards and wind fairings can improve the aerodynamic performance to some extent, while horizontal guide plates with 5% of the total deck width show a significant influence on the flutter stability and VIV. A wind fairing with an angle of $55^{\circ}C$ showed the best overall control effect but led to more lock-in regions of VIV. The combination of vertical stabilisers and airflow-depressing boards was found to be superior to other countermeasures and effectively boosted aerodynamic performance; specifically, vertical stabilisers significantly contribute to improving flutter stability and suppressing vertical VIV, while airflow-depressing boards are helpful in reducing torsional VIV.

• Wind and Structures
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• 제38권5호
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• pp.399-410
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• 2024

Long-span suspension bridges located in typhoon-prone regions face significant risks of flutter instability, particularly in girder erection. Despite the implementation of aerodynamic countermeasures designed for the service stage, the flutter stability of bridge in girder erection may not meet the required standards. Nowadays, the double-deck truss girder is increasingly common in practical engineering which exhibits different performance from the single-deck truss girder. To gain insights into the flutter performance of this girder type and determine temporary aerodynamic countermeasures for flutter suppression in girder erection, wind tunnel tests were conducted. The effects of affiliated members on the flutter performance were first examined. Subsequently, different aerodynamic countermeasures were designed and their effectiveness was tested. The results indicate that the stabilizers above and below the upper and lower decks are the most effective for the flutter stability of bridge at positive and negative angles of attack, respectively. The higher the stabilizers are, the better the effect on flutter suppression achieves. Considering the feasibility in practical engineering, a temporary stabilizer above the upper deck was considered. It is expected that the results could provide references for the aerodynamic design of double-deck truss girder during erection.

• Wind and Structures
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• 제3권4호
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• pp.267-277
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• 2000

This paper aims to describe the aerodynamic vibrations of various structural elements of bridges, which are particular issues at present. The aerodynamic countermeasures for those vibrations are also discussed considering the generation mechanisms of the aerodynamic instabilities. In this paper, an example of vortex-induced oscillation of bridge deck and its lesson are discussed. Next, the wind-induced cable vibration and its aerodynamic countermeasures are reviewed. Then, the aerodynamic characteristics on two edge girders and their feasibility for application to long span cable-stayed bridges are considered. Furthermore, the bridge decks for future long span bridges are proposed and their aerodynamic characteristics are also discussed.

• Wind and Structures
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• 제30권5호
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• pp.499-509
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• 2020

The aeroelastic stability of a long-span suspension footbridge with a bluff deck (prototype section) was examined through static and dynamic wind tunnel tests using a 1:10 scale sectional model of the main girder, and the corresponding aerodynamic countermeasures were proposed in order to improve the stability. First, dynamic tests of the prototype sectional model in vertical and torsional motions were carried out at three attack angles (α = 3°, 0°, -3°). The results show that the galloping instability of the sectional model occurs at α = 3° and 0°, an observation that has never been made before. Then, the various aerodynamic countermeasures were examined through the dynamic model tests. It was found that the openings set on the vertical web of the prototype section (web-opening section) mitigate the galloping completely for all three attack angles. Finally, static tests of both the prototype and web-opening sectional models were performed to obtain the aerodynamic coefficients, which were further used to investigate the galloping mechanism by applying the Den Hartog criterion. The total damping of the prototype and web-opening models were obtained with consideration of the structural and aerodynamic damping. The total damping of the prototype model was negative for α = 0° to 7°, with the minimum value being -1.07%, suggesting the occurrence of galloping, while that of the web-opening model was positive for all investigated attack angles of α = -12° to 12°.

• Wind and Structures
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• 제38권2호
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• pp.93-107
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• 2024

A π-shaped composite deck in the form of an open section is a type of blunt body that is highly susceptible to wind loads. To investigate its vortex-induced vibration (VIV) performance, a large-scale (1/20) section model of a cable-stayed bridge with a main span of 650 m was tested in a wind tunnel. The vibration suppression mechanism of the countermeasures was analyzed using computational fluid dynamic. Experimental results demonstrate that the vertical and torsional VIVs of the original section can be suppressed by combining guide plates with a tilt angle of 35° and bottom central stabilizing plates as aerodynamic countermeasures. Numerical results indicate that the large-scale vortex under the deck separates into smaller vortices, resulting in the disappearance of the von Kármán vortex street in the wake zone because the countermeasures effectively suppress the VIVs. Furthermore, a full-bridge aeroelastic model with a scale of 1/100 was constructed and tested to evaluate the wind resistance performance and validate the effectiveness of the proposed countermeasures.

• Steel and Composite Structures
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• 제34권5호
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• pp.699-713
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• 2020

The aerodynamic performance of long-span cable-stayed bridges is much dependent on its geometrical configuration and countermeasure strategies. In present study, the aerodynamic performance of three composite cable-stayed bridges with different tower configurations and passive aerodynamic countermeasure strategies is systematically investigated by conducting a series of wind tunnel tests in conjunction with theoretical analysis. The structural characteristics of three composite bridges were firstly introduced, and then their stationary aerodynamic performance and wind-vibration performance (i.e., flutter performance, VIV performance and buffeting responses) were analyzed, respectively. The results show that the bridge with three symmetric towers (i.e., Bridge I) has the lowest natural frequencies among the three bridges, while the bridge with two symmetric towers (i.e., Bridge II) has the highest natural frequencies. Furthermore, the Bridge II has better stationary aerodynamic performance compared to two other bridges due to its relatively large drag force and lift moment coefficients, and the improvement in stationary aerodynamic performance resulting from the application of different countermeasures is limited. In contrast, it demonstrates that the application of both downward vertical central stabilizers (UDVCS) and horizontal guide plates (HGP) could potentially significantly improve the flutter and vortex-induced vibration (VIV) performance of the bridge with two asymmetric towers (i.e., Bridge III), while the combination of vertical interquartile stabilizers (VIS) and airflow-depressing boards (ADB) has the capacity of improving the VIV performance of Bridge II.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2011년도 춘계학술대회 논문집
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• pp.20-27
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• 2011

High-speed railway system is exposed to severe aerodynamic problems and has various requirements both on design and operation; 80% of running resistance is composed of aerodynamic drag, the cross-sectional area and portal shape of tunnel should be designed under aerodynamic consideration, and natural wind velocity should always be monitored to prevent the overturning of train by crosswinds. In addition, most of the aerodynamic problems are proportional to the running speed or square of the running speed. Thus, when the running speed of a high-speed railway system either on operation or under construction is to be increased, the aerodynamic problems should be assessed in advance and the countermeasures should be prepared to alleviate the aerodynamic problems to meet certain requirements. In this study, aerodynamic problems that could occur at speed up of high-speed line have been investigated and aerodynamic requirements to meet the increased operational speed have been studied referring the international and domestic rules, guidance, and recommendations.

• Wind and Structures
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• 제35권5호
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• pp.337-351
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• 2022

As central-slotted box decks usually have excellent flutter performance, studies on this type of deck mostly focus on the vortex-induced vibration (VIV) control. Yet with the increasing span lengths, cable-supported bridges may have critical wind speeds of wind-induced static instability lower than that of the flutter. This is especially likely for bridges with a central-slotted box deck. As a result, the overall aerodynamic performance of such a bridge will depend on its wind-induced static stability. Taking a 1400 m-main-span cable-stayed bridge as an example, this study investigates the influence of a series of deck shape parameters on both static and flutter instabilities. Some crucial shape parameters, like the height ratio of wind fairing and the angle of the inner-lower web, show opposite influences on the two kinds of instabilities. The aerodynamic shape optimization conducted for both static and flutter instabilities on the deck based on parameter-sensitivity studies raises the static critical wind speed by about 10%, and the overall critical wind speed by about 8%. Effective VIV countermeasures for this type of bridge deck have also been proposed.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2005년도 ICCAS
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• pp.1374-1378
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• 2005

Appropriate upward force is crucial for the pantograph on high speed train to collect current from the catenery system without separation. However, at high speed, large aerodynamic lifting force is generated by the contact plate and the arms of pantograph, which may cause wear of the contact wire. In this study, to confirm the interface performance of the pantograph on Korea High Speed Train, a method to measure the contact force of the pantograph was proposed and the related measurement system was developed. The forces acting on the pantograph were clarified and a procedure to calculate the aerodynamic lifting force was proposed. A special device was invented and applied to measure the lifting force. Measured contact forces were displayed by the developed system and evaluated according to the criteria. Countermeasures were also taken to reduce the contact force based on the results.

• Wind and Structures
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• 제23권1호
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• pp.45-57
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• 2016

Open-cross-section composite beam (OCB) tends to suffer vortex-induced vibration (VIV) due to its bluff aerodynamic shape. A cable-stayed bridge equipped with typical OCB is taken as an example in this paper to conduct sectional model wind tunnel test. Vortex-induced vibration is observed and maximum vibration amplitudes are obtained. CFD approach is employed to calculate the flow field around original cross sections in service stage and construction stage, as well as sections added with three different countermeasures: splitters, slabs and wind fairings. Results show that flow separate on the upstream edge and cause vortex shedding on original section. Splitters can only smooth the flow field on the upper surface, while slabs cannot smooth flow field on the upper or lower surface too much. Thus, splitters or slabs cannot serve as valid aerodynamic means. Wind tunnel test results show that VIV can only be mitigated when wind fairings are mounted, by which the flow field above and below the bridge deck are accelerated simultaneously.