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Wind-induced stress analysis is essential for evaluating the local failure and fatigue damage of long-span bridges in wind-prone regions. Nevertheless, the accuracy of stress-level analysis can be affected by the choice of wind loading and structure models. This study formulates three scenarios to calculate the wind-induced response of a long-span bridge, incorporating two types of wind load models (lumped force or distributed force) and two types of finite element (FE) models (spine-beam or substructure). Specifically, Case 1 employs the lumped force and beam model, Case 2 adopts the lumped force and substructure model, and Case 3 utilizes the distributed force and substructure model. The aerodynamic parameters for forces and POD pressure modes are obtained through wind tunnel tests. By comparing the wind-induced structural response in terms of global behavior (displacement, acceleration) and local behavior (stress), the influence of wind loading and structure models is discussed. The findings reveal that employing a simplified beam model underestimates local stress, and neglecting wind load distribution leads to further underestimation. Therefore, the refined FE model and distributed wind load models are recommended for the precise assessment of wind-induced stresses in long-span bridges. [ABSTRACT FROM AUTHOR]

The continuous increase in traffic volume requires wider single box girders for long-span cable-supported bridges. Flutter and aerostatic instability are challenging issues for these flexible bridges, especially when they are located in typhoon-prone regions. Aerodynamic countermeasures such as vertical and horizontal stabilizers, which are convenient in operation, saving in cost, and effective in the enhancement of flutter performance, are usually employed to withstand the wind environment requirement. This study investigates the aerodynamic and aerostatic effects of upper central vertical stabilizers (UCVS), lower central vertical stabilizers (BCVS), horizontal stabilizers (HS), and their combinations on two wide single box girders with an aspect ratio larger than 12 at various angles of attack (AOAs). The optimal layouts of stabilizers for the enhancement of flutter performance are studied using a series of wind tunnel tests. Their control mechanisms are examined and discussed using flutter derivatives and step-by-step (SBS) method. A new index of nominal torsional center (NTC) is proposed to intuitively describe the flutter modality. The correlations among different indexes of flutter modality, flutter derivatives, and Ucr are further analyzed. The static coefficients of the bridge girders and the aerostatic performance of the bridge with or without stabilizers are also analyzed. Experiment results show that the values of Ucr for 4- and 5-m-high single box girders increased by 13.9% and 46.3%, respectively, after the hybrid installation of UCVS, BCVS, and HS at their optimal conditions. The analytical solutions indicate that the installation of different stabilizers changes the variation trend of the aerodynamic damping ratio with the wind speed to increase or reduce the flutter boundary. Four flutter modality indexes including amplitude ratio (Ψ), phase difference (ψ), energy participation level (Ph), and NTC are all found that have no obvious correlations with Ucr. The static analysis on a three-dimensional bridge showed that the optimal stabilizer schemes for flutter have insignificant effects on aerostatic performance. [ABSTRACT FROM AUTHOR]

Quantifying vortex-induced forces is crucial to understanding vortex-induced vibration (VIV) in long-span bridges, but it is infeasible to measure directly on structures in situ. Existing structural health monitoring systems, which rely on accelerometers, only capture structural responses at discrete points. This study employs common Bayesian filters (a Kalman filter and RTSS smoother) with acceleration output data to estimate vortex-induced forces and the system's multimodal states. Additionally, a Gaussian process exponential-periodic latent force model (EP-LFM) is introduced to inform the Bayesian filters about the cyclic nature of VIV. Unlike conventional methods that rely on wind tunnel tests, which may not fully capture the complexity of VIV at full scale, the use of full-scale response data enables the tuning of VIV models directly on operational bridges. The 1650 m long Xihoumen Bridge is introduced as a case study for its sensitivity to VIV. The analysis revealed that the estimates of vortex-induced forces are stable and do not accumulate errors, clearly distinguishing between buffeting and VIV responses across multiple modes. Analysis of ten VIV events is performed and used to determine equivalent aerodynamic damping ratios, which may serve as targets for damping requirements to avoid excessive VIV. The results indicate that the suggested framework can be seamlessly incorporated into the online monitoring system for VIV. [ABSTRACT FROM AUTHOR]

This study proposes a general modeling framework for large-amplitude vertical-torsional coupled nonlinear flutter, which may have great potential to be applicable to most bridge decks. The framework mathematically models various nonlinear behaviors (including mechanical nonlinearity, non-wind-induced aerodynamic nonlinearity, amplitude-dependent flutter complex mode and wind-induced aerodynamic damping, and nonlinear coupling of vertical aerostatic deformation) present in free-vibration wind tunnel tests. The identification of parameters of all concerned nonlinear models in this framework only requires displacement responses from simple free-vibration wind tunnel tests, which makes it convenient for practical engineering applications. Meanwhile, a corresponding numerical solving procedure for nonlinear aeroelastic responses is also developed. The feasibility of the proposed modeling framework is then cross-validated through wind tunnel tests with a novel large-amplitude testing device, and the coupled vertical aerostatic deformation observed under large amplitudes can be well predicted by an asymmetric lift force model in the framework. Then, based on the validated nonlinear aerodynamic force model, a three-dimensional (3D) nonlinear flutter analysis method for full-bridge is established, and the influences of 3D effects on nonlinear flutter are investigated. The results show that ignoring 3D effects will significantly misestimate the nonlinear flutter amplitudes. Finally, based on the results of wind tunnel tests, it is verified that the proposed modeling framework has the ability to predict nonlinear bifurcation behavior (i.e., the final state of vertical and torsional vibrations at a given wind speed depends on the initial conditions) that occurs in 2DOF (two-degree-of-freedom) coupled flutter. [ABSTRACT FROM AUTHOR]

Currently, typhoon-related performance of long span bridges usually focus on a specific wind record such as wind speed and turbulence intensity during a full typhoon, however, the inter-correlation among wind characteristic parameters under typhoon wind climate is ignored. The existing investigation about structural responses during typhoon attacks are still limited at case-study analysis, and hardly provide a generalized framework to evaluate the structural performance especially for typhoon landing whole process. This study utilizes the measured wind speeds of the strong typhoon "Hagupit" to establish a unified typhoon parametric model, during which the correlation of typhoon wind parameters including angle of attack (AoA), turbulence intensity, integral length scale and mean wind speed were taken into consideration. The measured typhoon process charactered with center-through effect with M-type average wind speed curve. Furthermore, the structural performance of long-span bridges with different spans from 1500 m to 2500 m main span was systematically studied. The aerodynamic parameters of the bridge deck section, including the aerostatic coefficients, flutter derivatives at different AoAs, and aerodynamic admittance under different oncoming flow conditions were identified through wind tunnel tests. Finally, the wind-induced buffeting performance was calculated by the buffeting frequency domain algorithm, showing various structural wind effect characteristics during the typhoon landing whole process. The maximal buffeting response is not necessarily related with the wind speed, and other wind characteristics especially turbulence intensity and AoA, etc. also affect on the results. [ABSTRACT FROM AUTHOR]

In the event of partial damage to the wind barriers installed on a bridge, the wind loads of a train will change abruptly as they enter and exit the damaged area, resulting in the deterioration of the train running safety. This study aimed to assess the running safety of a CRH2 high-speed train traversing a four-tower cable-stayed bridge with damaged wind barriers. Formulas were deduced for the static and dynamic wind loads on the bridge and train and their combined effect. The aerodynamic coefficients of the train and bridge were obtained through wind tunnel tests of a train–bridge sectional model, and a model of the wind–train–track–bridge coupled system was established using multi-body dynamics and the finite element method. The effects of the length of the damaged area and average wind speed on the train running safety were investigated based on the proposed model. The results reveal that the car body lateral displacements and accelerations reach their maximum amplitudes when the vehicles enter and leave the damaged area, respectively. The amplitude of the car body lateral displacement increases as the length of the damaged area increases, until it reaches 72 m. The wheel load reduction rates (WLRRs) and derailment coefficients (DCs) of the vehicles increase owing to the damage of the wind barriers; however, the percentage increases for each vehicle are considerably different. The train can safely traverse the damaged area of wind barriers at a designed speed of 180 km/h when the average wind speed is lower than 10 m/s. When the average wind speed reaches 20 m/s, the train can still safely cross the damaged area if the length of the damaged area is less than 12 m. [ABSTRACT FROM AUTHOR]

This paper explores the nonlinear characteristics of the self-excited aerodynamic forces of a semi-closed box deck section to perfect the theory of aeroelastic response analysis. A numerical wind tunnel model was established based on the computational fluid dynamics (CFD) method. The heaving-pitching coupled motion is realized by loading user-defined function (UDF) and dynamic grid technology. The self-excited aerodynamic forces varying with amplitude are identified and analyzed, and the reliability of the aerodynamic results obtained by numerical simulation is verified in the wind tunnel test. In the heaving-pitching coupled motion, the results show that the nonlinear characteristics of aerodynamic forces, especially the aerodynamic moment, are mainly affected by the pitching motion. The phenomenon of high-order harmonic energy transfer is observed with the increase in pitching amplitude, and the main component of high-order harmonic can be determined by the pitching amplitude. The contribution of heaving motion to aerodynamic forces nonlinear components is small, but its influence on nonlinear characteristics is complex. Small amplitude heaving motion plays a positive damping role in heaving-pitching coupled motion, and its scope and effect of positive damping action are affected by pitching motion. The extreme value heaving amplitude of positive damping action is observed in the aerodynamic lift. [ABSTRACT FROM AUTHOR]

The plate-truss composite girder (PTCG) has commonly been used in the design of long-span bridges in recent years. However, most studies regarding flutter stability and related mitigation measures primarily focus on traditional plate-truss separated girders (PTSGs). In this paper, a comparative study is performed to investigate the differences between the flutter characteristics of the PTCG and PTSG via wind tunnel tests and computational fluid dynamic simulations. Upper and lower central vertical stabilizers are applied to the PTCG and PTSG to examine their flutter mitigation effects. The flutter and its mitigation mechanisms are preliminarily explored based on the time-averaged streamlines and flow structures around the truss girder sections. The results show that the PTCG has a better flutter performance at the most unfavorable attack angle of +3° compared with the PTSGs in their service state. The flutter mitigation effect of the upper central vertical stabilizers is much more significant than that of the lower central vertical stabilizers for the investigated truss sections. Moreover, both the upper and the lower central vertical stabilizers have better mitigation effects on the flutter of the PTSG compared with that of the PTCG. [ABSTRACT FROM AUTHOR]

The traditional method for calculating the buffeting response of long-span bridges follows the strip assumption, and is carried out by identifying aerodynamic parameters through sectional model force or pressure measurement wind tunnel tests. However, there has been no report on predicting the buffeting response based on the sectional model vibration test. In recent years, the author has proposed a method, based on the integrated transfer function, for predicting the buffeting response of long-span bridges through theoretical and full-bridge tests. This provided an idea for predicting the buffeting response based on the sectional model vibration test. Unfortunately, the effectiveness and accuracy of this method have not been proven or demonstrated through effective tests. To solve this problem, a long-span suspension bridge was taken as a background. Parameters such as aerodynamic admittance were identified through a sectional model force measurement test and the integrated transfer functions were identified through a sectional model vibration test. A taut strip model test was also conducted. Furthermore, the buffeting response prediction results based on three kinds of wind tunnel test techniques were compared. The results showed that if the strip assumption was established, the results of the three methods aligned well, and that selecting a reasonable model aspect ratio for the test could effectively reduce the influence of the 3D effect; moreover, identifying the integrated transfer function by the sectional model vibration test could effectively predict the long-span bridge buffeting response. Furthermore, when the strip assumption failed, the results of the traditional calculation method using 3D aerodynamic admittance became smaller. A larger result would be obtained by neglecting the influence of aerodynamic admittance. [ABSTRACT FROM AUTHOR]

As flutter is a very dangerous wind-induced vibration phenomenon, the mitigation and control of flutter are crucial for the design of long-span bridges. In the present study, via a large number of section model wind tunnel tests, the flutter performance of a superlong-span suspension bridge with a double-deck truss girder was studied, and a series of aerodynamic and structural measures were used to mitigate and control its flutter instability. The results show that soft flutter characterized by a lack of an evident divergent point occurred for the double-deck truss girder. Upper central stabilizers on the upper deck, lower stabilizers below the lower deck, and horizontal flaps installed beside the bottoms of the sidewalks are all effective in suppressing flutter for this kind of truss girder. By combining the structural design with aerodynamic optimizations, a redesigned truss girder with widened upper carriers and sidewalks, and double lower stabilizers combined with the inspection vehicle rails is identified as the optimal flutter mitigation scheme. It was also found that the critical flutter wind speed increases with the torsional damping ratio, indicating that the dampers may be efficient in controlling soft flutter characterized by single-degree-of-freedom torsional vibration. This study aims to provide a useful reference and guidance for the flutter design optimization of long-span bridges with double-deck truss girders. [ABSTRACT FROM AUTHOR]

The purpose of this study is to investigate the nonlinear torsional flutter of a long-span suspension bridge with a double-deck truss girder. First, the characteristics of nonlinear flutter are studied using the section model in the wind tunnel test. Different aerodynamic measures, e.g. upper and lower stabilizers and horizontal flaps, are applied to improve the flutter performance of the double-deck truss girder. Then, the full bridge aeroelastic model is tested in the wind tunnel to further examine the flutter performance of the bridge with the optimal truss girder. Finally, three-dimensional (3D) flutter analysis is performed to study the static wind-induced effects on the nonlinear flutter of the long-span suspension bridge. The results show that single-degree-of-freedom torsional limit cycle oscillations occur at large amplitudes for the double-deck truss section at the attack angles of 0 ∘ and + 3 ∘ . The upper and lower stabilizers installed on the upper and lower decks, respectively, and the flaps installed near the bottoms of the sidewalks can all effectively alleviate the torsional flutter responses. Meanwhile, it is found that the torsional flutter responses of the truss girder in the aeroelastic model test are much smaller than those in the section model test. The 3D flutter analysis demonstrates that the large discrepancies between the flutter responses of the two model experiments can be attributed to the additional attack angle caused by the static wind-induced displacements. This finding highlights the importance and necessity of considering the static wind-induced effects in the flutter design of long-span suspension bridges. [ABSTRACT FROM AUTHOR]

In the wind tunnel test of a long-span bridge model, to ensure that the dynamic characteristics of the model can satisfy the test design requirements, it is particularly important to accurately identify the modal parameters of the model. First, the stochastic subspace identification algorithm was used to analyze the modal parameters of the model in the wind tunnel test; then, Grubbs criterion was introduced to effectively eliminate outliers in the damping ratio matrix. Stochastic subspace identification algorithm with Grubbs criterion improved the accuracy of the modal parameter identification and the ability to determine system matrix order and prevented the modal omissions caused by determining the stable condition of the damping ratio in the stability diagram. Finally, Oujiang Bridge was used as an example to verify the stochastic subspace identification algorithm with Grubbs criterion and compare with the results of the finite element method. The example shows that the improved method can be effectively applied to the modal parameter identification of bridges. [ABSTRACT FROM AUTHOR]

Engineers, architects, planners and designers must carefully consider the effects of wind in their work. Due to their slender and flexible nature, long-span bridges can often experience vibrations due to the wind, and so the careful analysis of wind effects is paramount. Traditionally, wind tunnel tests have been the preferred method of conducting bridge wind analysis. In recent times, owing to improved computational power, computational fluid dynamics simulations are coming to the fore as viable means of analysing wind effects on bridges. The focus of this paper is on long-span cable-supported bridges. Wind issues in long-span cable-supported bridges can include flutter, vortex-induced vibrations and rain–wind-induced vibrations. This paper presents a state-of-the-art review of research on the use of wind tunnel tests and computational fluid dynamics modelling of these wind issues on long-span bridges. [ABSTRACT FROM AUTHOR]

In mountainous areas, more challenges are expected for the construction of long-span bridges. The flutter instability during erection is an outstanding issue due to flexible structural characteristics and strong winds with large angles of attack. Taking the suspension bridge as an example, the flutter stability of the bridge with different suspending sequences was investigated. First, the dynamic characteristics of the bridge during erection were computed by the finite element software ANSYS, along with the effects on flutter stability discussed. Then, different aerodynamic shapes of the bridge girder during erection were considered. The aerodynamic coefficients and the critical flutter state were determined by wind tunnel tests. Based on the above analysis, some structural measures are proposed for improving the flutter stability of the bridge during erection. The results show that the flutter stability of the bridge during erection is related to the suspending sequence and the aerodynamic shape of the girder. Owing to the structural dynamic characteristics, the bridge has better flutter stability when the girder segments are suspended symmetrically from the two towers to the mid-span. Considering the construction requirement that the bridge deck should be laid without intervals, this structural superiority is seriously weakened by the unfavorable aerodynamic shape of the girder. In order to improve the flutter stability of the bridge during erection, an effective way is to adopt some temporary structural strengthening measures. [ABSTRACT FROM AUTHOR]

In this article, a two-dimensional Lighthill aerodynamic model is first extended to three-dimensional space, and then combined with the larger Von Karman plate deformation theory, a model for predicting the critical flutter wind speeds of long-span bridges in the primary design is proposed. The predictions of the presented model are compared to the results of wind tunnel tests for five long-span bridges with different main girder section forms. After that, based on the proposed model, the effects of width to span ratio and thickness to span ratio on the critical flutter wind speeds of long-span bridges are investigated. The results show that the differences between the proposed model and wind tunnel tests are only 7%–14%. Therefore, the presented model can assess the flutter wind speed in preliminary design stages of a bridge. The results also reveal that width to span ratios between 1/30 and 1/10 and thickness to span ratios between 1/300 and 1/100 are optimal for long-span bridges. [ABSTRACT FROM AUTHOR]

Wind tunnel tests were performed on a 4:1 rectangular (REC) cylinder, a trapezoidal (TRA) girder, and a typical streamlined (STR) box girder to investigate the vortex-induced forces and their spanwise correlations. First, using the free vibration technique, the vortex-induced vibration responses and the Strouhal number were investigated at different Scruton numbers and attack angles. Then, the mean and standard deviations of the vortex-induced pressure coefficients of the three models were analyzed through simultaneous pressure measurements. The power spectral density and the spanwise correlation of vortex-induced pressures at some typical points were also studied. Finally, the spanwise correlations of vortex-induced forces acting on the three models in the cases of different vibration amplitudes and attack angles were investigated. The results show that the attack angle has a significant effect on the vortex-induced pressure distributions for the three types of girders. The second frequency components of the vortex-induced pressure occur near the trailing edge of the upper surface for the three types of sections. The correlation of vortex-induced force decreases with the increase in the oscillation amplitude for the REC model, but becomes larger for the TRA and STR models. With the increase in the attack angle, the spanwise correlations of vortex-induced forces on the three sections become weaker, especially for the REC model. [ABSTRACT FROM AUTHOR]

Aerodynamic countermeasures are widely used to control vortex-induced vibration (VIV) on long-span bridges. However, due to the lack of appropriate three-dimensional (3-D) VIV analysis approach, these countermeasures are usually installed along the entire span of the bridge deck, leading to excessive costs. This study proposes an optimization method for the spanwise layout of aerodynamic countermeasures, aiming to achieve an economical control scheme for multi-mode VIV. An improved mode-by-mode 3-D VIV analysis approach is developed based on the generalized polynomial model to predict the VIV responses of the bridge with different spanwise layouts of aerodynamic countermeasures. The genetic algorithm (GA) is then employed to search for the most economical layout scheme with constraints of limited multi-mode VIV responses. Two alternative types of search spaces for the optimization are presented. The effectiveness of this optimization method is demonstrated on a long-span suspension bridge in conjunction with finite element simulation and wind tunnel tests. The results show a noteworthy reduction in the use of aerodynamic countermeasures, thus highlighting the necessity of countermeasure layout optimization. • Optimize the spanwise layout of aerodynamic countermeasures to economically control vortex-induced vibration (VIV) on long-span bridges. • Introduce a mode-by-mode 3-D VIV analysis method for bridges with different spanwise layouts of aerodynamic countermeasures. • Determine the most economical countermeasure layout scheme for multi-mode VIV control by employing the genetic algorithm (GA). [ABSTRACT FROM AUTHOR]

Buffeting performance is growing sensitive to external and internal factors with increasing span of bridge. Aerodynamic admittance is an essential parameter in analyzing buffeting performance. In this paper, aerodynamic admittance in different conditions were conducted in wind tunnel tests by section model. Three kinds of aerodynamic admittance functions were used to calculating buffeting performance respectively. It is found that the aerodynamic admittance of streamlined deck is closely related to wind attack angle, and has a small difference at different wind speeds. However, the influence of aerodynamic admittance on buffeting performance is affected by the wind speed significantly. Under given conditions, adopting the Sears function as the admittance function of a similar streamlined box girder is reasonable, while the buffeting performance result obtained by adopting an admittance function as 1.0 is very conservative. [ABSTRACT FROM AUTHOR]

On the basis of the definition and the three-dimensional characteristics of an integrated transfer function, the transfer function identification method based on reasonable technical means considering the three-dimensional effect was proposed. An original method to predict the bridge buffeting responses directly using the integrated transfer function is presented and investigated by means of segmental model vibration tests. Taking a suspension bridge as the background, the integrated transfer function was identified using segmental model vibration tests, and the effect of span-width ratio on it was studied. The buffeting response test of a full-bridge model was carried out in two different wind fields. Further, the identified integrated transfer functions were applied to predict the buffeting responses of the full-bridge model. By comparing the results, it is demonstrated that the method using reasonable segmental model vibration tests to obtain the integrated transfer functions to predict the bridge buffeting responses was highly accurate. The feasibility of the proposed method according to segmental model vibration tests was verified through tests for the first time. The method can effectively improve the deviation of results arise from the inaccurate simulating of turbulent characteristics in the tests, and avoid the many limitations of pressure and force measurement methods. • The influence of the span-width ratio on the buffeting response prediction of bridges is investigated. • An accurate identification method of integrated transfer function via segmental model vibration test is provided. • A prediction method for bridge buffeting responses via segmental model vibration test is proposed. [ABSTRACT FROM AUTHOR]

Classical flutter of suspended bridge decks can be avoided if the torsional frequencies are lower than the vertical. Wind tunnel tests of single boxes and twin box section models with torsional natural frequencies above and below the vertical frequency has been conducted. Flutter was avoided in all tests where the torsional frequency was lower than the vertical. But too low torsional stiffness caused large static displacements of the girder at medium–high wind speeds and steady state oscillations driven by a combination of torsional divergence and stalling behavior at the critical wind seed. In order to design aerodynamically stable suspension bridges with low torsional natural frequencies it is suggested to increase the mass moment of inertia and provide adequate torsional stiffness by the main cables spacing. [ABSTRACT FROM AUTHOR]

High-fidelity CFD (computational fluid dynamics) numerical modeling offers an attractive alternative of VIV investigation for bridge deck. Conventional strategy to perform VIV prediction using CFD is to directly characterize the two-way coupled free vibration of structure and flow which could become dramatically expensive in computational cost. To bridge the gap, this study presents an efficient two-stage hybrid approach that combines a divergent vibration simulation for fast aerodynamic damping extraction and a nonlinear model to predict the VIV. A negative structural damping is imposed in the motion equation to intentionally create a divergent vibration which significantly accelerates the growth of motion and takes less than 1/3 of the elapsed time compared with a conventional VIV simulation whereas maintains reasonable accuracy in aerodynamic identification. A Π-shaped bridge deck is employed as a demonstration of the proposed approach. The modeled steady-state VIV performance is well validated against wind tunnel tests. The effect of negative damping on instantaneous flow field, surface pressure and amplitude prediction are discussed and the optimal damping ratio achieving balanced accuracy and efficiency is suggested. The proposed framework shows favorable efficiency while simultaneously retains satisfactory accuracy and is a potential numerical alternative of VIV investigation for bridge deck. • A two-stage framework that combines a divergent vibration simulation and a nonlinear model for VIV prediction is presented. • The proposed approach is well validated against wind tunnel tests on a Π-shaped bridge deck. • The presented framework shows favorable efficiency and satisfactory accuracy in VIV investigation for bridge deck. [ABSTRACT FROM AUTHOR]

With the assistance of typhoon field data at aerial elevation level observed by meteorological satellites and wind velocity and direction records nearby the ground gathered in Guangzhou Weather Station between 1985 and 2001, some key wind field parameters under typhoon climate in Guangzhou region were calibrated based on Monte-Carlo stochastic algorithm and Meng's typhoon numerical model. By using Peak Over Threshold method (POT) and Generalized Pareto Distribution (GPD), Wind field characteristics during typhoons for various return periods in several typical engineering fields were predicted, showing that some distribution rules in relation to gradient height of atmosphere boundary layer, power-law component of wind profile, gust factor and extreme wind velocity at 1-3s time interval are obviously different from corresponding items in Chinese wind load Codes. In order to evaluate the influence of typhoon field parameters on long-span flexible bridges, 1:100 reduced-scale wind field of type B terrain was re-illustrated under typhoon and normal conditions utilizing passive turbulence generators in TJ-3 wind tunnel, and wind-induced performance tests of aero-elastic model of long-span Guangzhou Xinguang arch bridge were carried out as well. Furthermore, aerodynamic admittance function about lattice cross section in mid-span arch lib under the condition of higher turbulence intensity of typhoon field was identified via using high-frequency force-measured balance. Based on identified aerodynamic admittance expressions, Wind-induced stochastic vibration of Xinguang arch bridge under typhoon and normal climates was calculated and compared, considering structural geometrical non-linearity, stochastic wind attack angle effects, etc. Thus, the aerodynamic response characteristics under typhoon and normal conditions can be illustrated and checked, which are of satisfactory response results for different oncoming wind velocities with resemblance to those wind tunnel testing data under the two types of climate modes. [ABSTRACT FROM AUTHOR]

To study the influence of integral scale on buffeting response of long-span bridge which cannot be taken into account in the passive turbulence wind tunnel test and to provide a reasonable evaluation of wind tunnel test result, taking a typical cable-stay bridge and a suspension bridge as samples and combining aerodynamic parameters of the section model in wind-tunnel test, the influence of turbulence integral scale and wind spectra on buffeting responses were studied in frequency domain. The results show that buffeting responses decrease with increase of integral scale at lower wind speed; while at higher wind speed, buffeting responses increase first and then decrease. After comparing the integral scales in wind tunnel test and in wind standard, the result shows that buffeting response in wind tunnel were overestimated at lower wind speed, but underestimated at higher wind speed. After comparing the influences of several frequently-adopted horizontal and vertical wind spectra on buffeting response, the result shows that the influence of different horizontal wind spectra can be neglected, but the influence of different vertical wind spectra should be taken into account. [ABSTRACT FROM AUTHOR]

Conventional models resolve the vortex-induced vibration (VIV) problem for long-span bridge with an essential assumption that the cross-section is uniform. When the cross-sections are altered in span-wise direction, i.e., inhomogeneous cross-section design, conventional approaches are inapplicable, and the global VIV becomes ambiguous and difficult to evaluate directly. This paper presents an integrated approach which combines the Scanlan's nonlinear VIV model and an aerodynamic damping model to characterize the global VIV for long-span bridge with inhomogeneous cross-section design. In the proposed approach, the Scanlan's nonlinear model is utilized to characterize the vortex-induced motivating force on cross-sections at lock-in whereas the aerodynamic damping model is employed to describe the air-induced hindering effect on cross-sections away from lock-in. The parameters in the integrated model are identified using either a 'decay-to-resonance' method or free decay vibration test via sectional model tests. The proposed approach is validated through a proof-of-concept wind tunnel experiment. An engineering practice of an urban rail-road long-span bridge with span-wise inhomogeneous cross-section design is demonstrated and discussed as an example. The VIV performance with and without considering inhomogeneous effects are evaluated and compared. The effects of various section deployment plans as well as their global performance are investigated and discussed. • An integrated approach is presented to investigate the global VIV of long-span bridge with inhomogeneous cross-sections. • The proposed approach combines Scanlan's nonlinear VIV model with a linear air-induced damping model. • The aerodynamic parameters of each cross-section are identified via sectional model wind tunnel tests. • The validation is performed on an inhomogeneous sectional testing model. • The effect of inhomogeneity and various cross-section deployment plans on global VIV amplitude are evaluated and discussed. [ABSTRACT FROM AUTHOR]

Split type box girder is a recommendable structural style for long-span cable-supported bridges due to its excellent aeroelastic stability. A major issue of this kind of girder is its susceptibility to vortex-induced vibration (VIV), which has not been adequately investigated. This paper presents an experimental study on VIV of a triple-box girder with three different web modifications (namely curved web and linear-type webs with different slopes). Both small- and large-scale sectional models were employed for wind tunnel tests considering the Reynolds number effect. Results indicated that the triple-box girder showed poor VIV performances in both construction and completed phases. Generally, linear-type web was superior to curved web in terms of VIV performance. Increasing the structural damping and turbulence intensity of incoming flow were helpful for VIV mitigation. Geometric profiles and arrangement of appurtenant facilities on the girder have significant effects on the VIV performance. Aerodynamic optimal schemes were proposed for VIV mitigation both in construction and completed phases. Obvious discrepancies in VIV responses were observed between the small- and large-scale tests for several scenarios. Possible factors being responsible for the discrepancies were Reynolds number, turbulence intensity, nonlinearity of model structural damping, blockage ratio and geometric accuracy of the sectional models. [ABSTRACT FROM AUTHOR]

• The inhomogeneous wind fields at the bridge site were measured in detail by wind tunnel tests. • The wind coherence along the bridge girder was determined in three situations. • The inhomogeneous wind attack angles decrease the critical flutter velocity of the bridge. The wind characteristics as well as the flutter performance of a long-span suspension bridge located in a deep-cutting gorge terrain were investigated in the present study. To address the spatially variable or inhomogeneous wind fields (InWF) at the bridge site, a large terrain model surrounding the bridge site was installed in a large-scale wind tunnel. The mean wind speed, turbulence intensity, wind attack angle, wind power spectral density (PSD) and wind coherence all varying along the bridge girder were measured and analyzed in detail. Also, the stationarity and the cumulative distribution functions of the turbulent flow along the bridge girder were evaluated. Then, the flutter performance under four different InWF cases were comprehensively investigated. The results show that the turbulence components u as well as w along the bridge girder can be considered as stationary Gaussian stochastic processes. The wind PSDs significantly vary along the bridge girder, and the traditional wind PSDs obtained from the relatively flat terrains are not accurately applicable here. A two-parameter root coherence function model was developed to address the complex wind coherence over the deep-cutting gorge, and the wind coherence along the bridge girder was determined in three situations. When the wind fields along the bridge girder are assumed as homogeneous, the critical flutter velocity is overestimated by 10.1%. When inhomogeneous wind attack angles are considered, the contribution of the first symmetrical torsional mode to the critical flutter state become larger. [ABSTRACT FROM AUTHOR]

In this paper, the effects of the turbulence integral scale on the buffeting response of a long-span suspension bridge are studied via the proposed three-dimensional (3D) two-wavenumber buffeting analysis method. The root mean squares (RMS) of the buffeting lift and displacement of the streamlined bridge girder are analyzed in cases with different ratios of the turbulence integral scale to the half-width of the bridge girder (γ) and mean wind speeds. To achieve a deeper understanding of the effects of the turbulence integral scale, the spectra of wind fluctuations, buffeting forces and vertical buffeting displacements for typical ratios of γ and mean wind speeds are compared. The results demonstrate that the equivalent buffeting lift per unit span and vertical buffeting displacement show different variation trends as γ increases. The effect of the turbulence integral scale on the buffeting lift forces is independent of the mean wind speed, and becomes more significant for the vertical buffeting displacements at high mean wind speeds in cases with small values of γ. The effectiveness and accuracy of the numerical analysis is verified by full-bridge aeroelastic wind tunnel tests in large integral scale turbulent fields. The present study shows that it is essential to consider the effects of the turbulence integral scale on the buffeting responses of long-span bridges. To achieve reliable results, accurate estimations and appropriate simulations of γ are of high importance in both numerical analysis and wind tunnel tests for the buffeting predictions of long-span bridges. [ABSTRACT FROM AUTHOR]