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This study delves into the flutter mechanism of a 5,000 m bridge with a wide-slotted deck, finding that the motion is self-sustained and not violently destructive. The system damping ratio is not fixed, and only one stable orbit exists. High-resolution PIV experiments at an experimental wind speed of 10.5 m/s measured the static and dynamic flow fields on the windward and leeward decks. The static results showed leading-edge separation on the windward deck within the reference range, while separation on the leeward deck was difficult to observe. Dynamic testing identified instantaneous vortices around the windward/leeward deck at each phase, with no signs of vortices in the wind speed vectors at all phases after phase-averaging, indicating that the vortex drift hypothesis is not valid. The analysis of the streamline pattern revealed periodic variations in leading-edge separation size and reattachment length on the windward deck during the vibration process, while the leeward deck showed consistently inconspicuous changes. Further examination uncovered a peculiar behavior in the horizontal wind speed profile on the leeward deck during the vibration process, attributed to dynamic changes in the height difference between the windward and leeward decks during flutter. The study suggests that the unusual wind speed profile on the leeward deck is caused by the dynamic changes in height difference between the windward and leeward decks during the flutter process, resulting in additional wind loading. These findings shed light on the complex dynamics of bridge flutter and have implications for the design and maintenance of long-span bridges. • Self-sustained flutter seen in 5,000 m bridge with wide-slotted deck. • Sectional model tests validate bridge deck's aerodynamic nonlinearity. • Successful PIV measurements capture dynamic flow of deck during LCO stage. • PIV tests debunk vortex drift theory, proving flutter's independence from vortices. • Measured periodic changes in separation and inflow during self-sustained flutter. [ABSTRACT FROM AUTHOR]

In the complex wind environment of canyon regions, different kinds of bridge deck gratings (BDGs) are often used as novel aerodynamic countermeasures to improve the wind-resistance performance of long-span suspension footbridges. However, how to design reasonable BDGs to effectively improve the aerodynamic stability of long-span suspension footbridges is still an urgent problem to be solved, and there is no literature reporting on it. Therefore, in this study, according to a long-span suspension footbridge with a streamlined double-side box girder (SDSBG) and BDGs, the section models with different percentages of opening (β) and layouts of BDGs were made, and then the force- and vibration-measured tests were performed to study the influence of the layouts and β of BDGs on the aerostatic and flutter stability. Furthermore, the influence mechanism of BDGs on the flutter stability was investigated, and the optimal β and layouts of BDGs were also proposed. So, it is found that: when 0% ≤ β ≤ 22% (especially β = 11%), BDGs are unfavorable to the aerodynamic stability; when β ≥ 44%, the aerodynamic stability can be significantly improved by using BDGs; moreover, the layouts of Cases O (β reaches the maximum) and S (two strips of BDGs installed along the longitudinal direction) are more beneficial to the aerodynamic stability. Therefore, the optimal β and layouts of BDGs beneficial to the aerodynamic stability are β ≥ 44% and the layouts of Cases O and S, respectively, and the studies in this manuscript can provide a meaningful reference for the wind resistance design of long-span suspension footbridges in the future. [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 this study, an experimental investigation was conducted to investigate the control effect of self-issuing jets — positioned on the lower inclined panels of a bridge deck — on suppression of vertical vortex-induced vibrations (VIVs). Two cases were considered, i.e., decks with and without auxiliary attachments (handrails and maintenance rails), corresponding to the serviceability and construction period, respectively. The vertical oscillating response, surface pressures, and aerodynamic forces are considered to reveal the control mechanism of self-issuing jets on the flow field around the section model. The results demonstrate that the self-issuing jet method effectively suppresses the VIV of the streamlined deck under an angle range of attack of -5 – 5° by reducing the fluctuating surface pressure and vortex-excited lift. For the bridge deck with attachments, no VIV is observed under the effect of self-issuing jets, indicating that this method can also fully suppress the VIV excited by the motion-induced vortex. • Passive jet method is proposed for optimizing aerodynamic performances and vortex-induced vibration of a bridge deck. • Jet control effect on aerodynamics of the deck during construction and service stage is analyzed. • Three-dimensional changes in local pressure distributions are focused. [ABSTRACT FROM AUTHOR]

The assessment of buffeting response of long span bridges relies significantly on the aerodynamic admittance and spanwise coherence functions of buffeting forces acting on bridge decks. This study presents a novel approach to derive admittance and coherence functions of buffeting lift on bridge decks, utilizing wind tunnel measurement of forces on spanwise distributed segments. The approach is developed by establishing connections of the power spectrum and coherence function of segmental lift with the admittance and coherence functions of strip lift. This study also explores the direct estimation of the generalized buffeting forces on long span bridges from the segmental force, eliminating the need of extracting admittance and coherence functions of strip force. The methodology is firstly validated for a thin plate with theoretical force information, follow by its application to a twin-box bridge deck using wind tunnel data. The investigation assesses the influence of a pre-assumed coherence model on the identified admittance and coherence functions and its consequential impact on the generalized buffeting forces of long span bridges. The proposed approach offers a practical and efficient means to quantify buffeting forces acting on bridge decks with intricate configurations, such as truss sections, where surface pressure measurement may pose challenges. • This study presents a novel approach to derive the admittance and coherence functions of buffeting lift on bridge decks, utilizing wind tunnel measurement of forces on spanwise distributed segments. • The approach is developed by establishing connections of the power spectrum and coherence function of segmental lift with the admittance and coherence functions of strip lift. • This study also explores the direct estimation of generalized buffeting forces of long span bridges from segmental force, eliminating the need for extracting admittance and coherence functions. • The approach is initally verified using a thin plate where theoretical results are available. It is then applied to a twin-box bridge deck using wind tunnel data. • The investigation assesses the influence of a pre-assumed coherence model on the identified admittance and coherence functions and the generalized buffeting forces of long span bridges. [ABSTRACT FROM AUTHOR]

An accurate assessment of the driving comfort and safety of road vehicles moving on a long-span bridge subjected to vortex-induced vibration (VIV) is essential for bridge administrators to decide whether the bridge should be closed to traffic. However, previous assessments often ignore the aerodynamic interference between the road vehicles and the bridge deck subjected to VIV. In this study, a specific wind tunnel model is developed to explore the aerodynamic interference between road vehicles and twin-box bridge deck during VIV. The vortex-induced force (VIF) and vortex-induced response (VIR) of the twin-box bridge deck and the aerodynamic forces on the vehicle were simultaneously measured. The influence of the vehicles on the VIV of the deck was investigated, and the influence of the deck vibration on the aerodynamic forces of the vehicle was also explored. The results show that the VIR and VIF of the bridge deck were generally reduced, depending on the type, position, and number of vehicles. The aerodynamic forces of vehicles could be amplified due to the deck vibration. These findings supplement the database of vehicle aerodynamic coefficients for assessing the driving comfort and safety of road vehicles moving on a long-span bridge subjected to VIV. • A specific wind tunnel test model was developed to explore the vehicle-bridge aerodynamic interference during VIV. • The VIF and VIR of the bridge deck and the aerodynamic forces on the vehicle were simultaneously measured. • The influence of the deck vibration on the aerodynamic forces of the vehicle was explored. • The type, position, and number of vehicles have significant impacts on the VIF and VIR of the bridge deck. • The aerodynamic forces on the vehicle vary with its position on the bridge, VIR, and wind angle of attack. [ABSTRACT FROM AUTHOR]

In this study, aerodynamic interference effects (AIE) on the vibration response, aerostatic coefficient (AC) and vortex-induced vibration (VIV) mechanism of the triple-separated decks under different incoming wind directions and vertical distances were investigated via wind tunnel tests and numerical simulations, respectively. The test results show that the AIE increases the displacement of VIV, and the VIV responses reaches maximum value under S/H = −1.0 (S is the vertical distance between the centers of RB and HB decks, and H is the height of RB deck) when the RB deck is on the windward side (the maximum displacements of VIV are 193.86% and 37.30% higher than the case of single RB deck and S/H = 0.0, respectively). The pressure distribution and flow structure show that the scale of vortex that alternately shed off from the tail of the deck becomes stronger and the fluctuating pressure coefficient increases under AIE, which increase the VIV amplitude of the RB deck and cause the VIV of HB decks. The experimental and numerical results indicated that the aerostatic coefficients (AC) of the leeward girder are more affected by the AIE. The interference factor (IF) of drag coefficient (C D) is far less than 1.0 under the case of F-5 (S/H = 0.0). • The aerodynamic interference effects (AIE) on the vibration responses and aerostatic coefficients of two parallel bridge with triple-separated decks are investigated by wind tunnel tests and numerical simulations. • The effects of incoming wind direction and vertical distance on AIE are considered. • The vortex-induced vibration (VIV) mechanism under AIE is analyzed by the pressure distribution and the static flow structure. [ABSTRACT FROM AUTHOR]

Permeable surfaces are nowadays widely adopted in the construction industry, with applications ranging from wind shields for bridge decks to the external layer of permeable double skin facades. However, due to the large scale separation between the overall structure dimension and the size of the pores, their modelling in CFD simulations is still extremely challenging and over-simplified homogenized models are often used in practice. Inspired by previous studies, the authors recently proposed a generalization of the well-known pressure-jump approach which accounts for flow deflections, denoted as pressure–velocity jump, PVJ. In this study, the derivation of the PVJ approach is briefly recalled and contextualized in the existing literature. Then, we use PVJ to study the influence of a lamellar screen positioned upstream of a ground-mounted obstacle using 2D URANS. In particular, simulations are performed using the proposed PVJ approach and Explicit Models, EM , in which lamellae are explicitly modelled, for square and a rectangular obstacles. Results show a good agreement between EM and PVJ based models, confirming the high potential of the proposed technique. • A lamellar screen upstream of an obstacle is simulated using 2D-URANS. • The lamellar screen is simulated adopting the Pressure–Velocity Jump, PVJ approach. • Comparisons are made between explicit simulations of the lamellar screen and PVJ based models. • The upstream position of the lamellar screen is varied as well as the shape of the obstacle. [ABSTRACT FROM AUTHOR]

Monitoring the wind-induced lateral displacement (WLD) of the bridge deck is crucial for structural health monitoring (SHM) of suspension bridges. An accurate WLD prediction model can aid the bridge SHM systems in abnormal data detection and reconstruction, structural response estimation under specific wind events, and structural condition assessment. However, WLD prediction faces challenges due to stochastic wind action and complex aerodynamic effects acting on the bridge deck. To address this, a deep learning-based framework was proposed for predicting the WLD response of the suspension bridge deck. This framework decomposed the WLD response into two components, namely the quasi-static and the dynamic one. Two separate deep-learning tasks were employed to predict these components using the lateral wind speed as input. In Task 1, a recurrent neural network (RNN) based on the gated recurrent unit (GRU) was built, whereas a fully convolutional neural network (CNN) based on U-Net was built in Task 2. Novel loss functions tailored to each task were established to facilitate accurate predictions. Measured data from the SHM system of the Jiangyin Yangtze River Bridge, China, was used as a case study to verify the proposed predictive framework's feasibility and high accuracy. The extreme value-weighted loss function in Task 1 enhanced the prediction accuracy for the extreme quasi-static WLD, while the time-frequency cross-domain loss functions in Task 2 effectively integrated the prediction accuracies in both time and frequency domains for the dynamic component of WLD. However, trade-offs were identified between the prediction errors of extreme and non-extreme values, as well as between the time- and frequency-domain prediction accuracies. • A deep learning framework is proposed for predicting wind-induced lateral displacement (WLD) responses. • Extreme value-weighted loss functions improve the prediction accuracy for the extreme quasi-static WLD. • Cross-domain loss functions ensure both the time- and frequency-domain accuracy for the dynamic WLD. • Trade-offs exist between prediction errors of extreme and non-extreme values, as well as between time- and frequency-domain prediction accuracies. [ABSTRACT FROM AUTHOR]

Aeroelastic flutter identification of a two-dimensional bridge deck section using time domain techniques is studied. Aeroelastic simulations are performed using the aeroelastic solver available in open source OpenFOAM 5.0, wherein aerodynamic loads are computed using Unsteady Reynolds Average Naiver–Stokes (URANS) solver. The bridge deck section, modelled as a rigid body, exhibits pitch and heave degrees of freedom. Time domain system identification techniques, which include VAR and ERA (Vector auto-regressive and Eigensystem realization algorithm), are used to extract frequency and damping parameters from the aeroelastic response for various wind speeds. Two approaches are used for identification of the flutter boundary. The first consists of tracking the behaviour of damping and identifying the speed at which damping vanishes. The second approach is based on the flutter margin for discrete-time system (FMDS), which exhibits a linear behaviour with dynamic pressure in the vicinity of flutter. Results presented indicate that the ERA yielded slightly better estimates of damping compared to VAR. Furthermore, the FMDS parameter provided a reasonable estimate of the flutter boundary using only two data points, suggesting that this is an efficient strategy (as compared to tracking the damping) for flutter identification when the cost per aeroelastic response data point is high. • Flutter speed of bridge deck section is obtained using time domain CFD method. • Aeroelastic simulations done using OpenFOAM 5.0. • System identification was done using ERA and VAR. • Flutter speed located using damping, and also by using the flutter margin concept. • Flutter margin reduces the number of CFD simulations required to locate flutter. [ABSTRACT FROM AUTHOR]

This paper aims to analyse the driving safety of road vehicles travelling over long-span bridges under crosswinds in a more reasonable manner by considering the aerodynamic interference from the bridge (which has been neglected in previous studies). Firstly, based on the overset dynamic mesh technique in CFD simulations, the aerodynamic coefficients of three representative road vehicles were investigated for moving on a twin-box girder bridge deck and flat ground, respectively. Subsequently, taking a superlong cable-stayed bridge as an example, the dynamic response of the wind-vehicle-bridge system was calculated using the separation iterative method, and the effects of aerodynamic interference, location of traffic lanes, wind angle of attack, travelling speed, and wind speed on driving safety were analysed according to the contact forces of the wheels. The results show that aerodynamic interference has a substantial impact on driving safety, which affects not just the accident wind speeds but also the type of accidents for high-sided vehicles. Finally, a four-level traffic-control strategy for the investigated bridge was developed according to the minimum accident wind speed in cases considering aerodynamic interference, which can provide a reference for operational decision-making for long-span bridges with similar geometric characteristics in crosswind environments. • Aerodynamic coefficients of vehicles are obtained for moving on the bridge deck and flat ground, respectively. • Criteria for determining wind-induced accidents in road vehicles have been developed. • Critical wind speeds of vehicles with and without considering the aerodynamic interference of the bridge are compared. • A four-level traffic control strategy is developed for the investigated bridge. [ABSTRACT FROM AUTHOR]

Aerodynamic forces of the Great Belt Bridge are mitigated using deep reinforcement learning (DRL) based active flow control (AFC) techniques at a Reynolds number of 5 × 1 0 5 in this study. The flow control method involves placing a suction slit at the bottom of the trailing edge of the bridge. The DRL agent as a controller is able to optimize the velocity of the suction to reduce the fluctuating coefficients of bending moment, drag, and lift by 99.1%, 73.7%, and 95.8% respectively. To reduce the high computational demands associated with DRL-based AFC training, this study integrates transfer learning technique into DRL, which calls transfer learning based deep reinforcement learning (TL-DRL) method. Specifically, the transfer learning method based on a DRL pre-trained model trained with a coarse mesh scheme is implemented. Results indicate that with TL-DRL method, the training cost can be reduced by 53%, while achieving the same control strategy and control effect as the DRL training from scratch. This study shows that the TL-DRL based flow control method is highly effective in reducing aerodynamic forces on long-span bridges. Furthermore, TL-DRL based flow control approach can adapt flexibly to different flow field environments, ultimately enhancing energy utilization efficiency. • This paper proposed a method for training an active flow control strategy of bridges. • A deep reinforcement learning (DRL) algorithm was employed for flow control training. • Transfer learning based DRL (TL-DRL) was employed to save computational resources. • TL-DRL based flow control is effective in reducing aerodynamic forces on bridges. • The flow control strategy trained by TL-DRL adaptively changes with the flow field. [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]

Flutter derivatives are commonly used to describe the behavior of the self-excited force. Based on them, most existing analyzing methods can reveal the overall process of the flutter evolution very well but are not so good at describing the internal mechanism combining with the aerodynamic pressure. To quantify the contributions from each zone of the deck's surface, a novel definition of Surface-Flutter-Derivatives (SFDs) are introduced. The wind-induced changes of the mode characteristics are allocated to different parts of the deck's surface, with the help of further derivations based on Chen's bimodal flutter stability expressions. Verification of the derived formulas are carried using the Computational-Fluid-Dynamics (CFD) method, based on deck shape and dynamic characteristics of the Great Belt Bridge. Next, the SFD's advantages in exploring the weights of the self-excited force's components and investigating the stabilizer's control mechanism on the bimodal flutter are demonstrated. Similar routings could be helpful when exploring the mechanism of other passive aerodynamic appendages. • Surface-Flutter-Derivatives are used to quantify the contributions of the deck's surface to the self-excited force. • The wind-induced changes of the damping and frequency are allocated to different zones of the deck's surface. • Numerical cases are conducted to investigate the control mechanism of stabilizer. [ABSTRACT FROM AUTHOR]

Due to the windless-air-induced added mass and damping effects, the mechanical frequency and damping ratio of a bridge deck model in wind tunnel test are usually under-estimated and over-estimated, respectively. In this study, the vertical and torsional added mass and damping and their effects on the mechanical frequency and damping ratio of an ideal plate and five typical bridge decks are thoroughly investigated based on single degree-of-freedom free vibration numerical simulations. The aerodynamic forces are linearly expressed as functions of vibrating accelerations, velocities, added mass coefficients, and added damping coefficients. The discrepancies between two-dimensional (2D) and three-dimensional (3D) simulations are found to be small. The numerical simulation accuracy is validated through comparison with the results from the Theodorsen expression and forced vibration simulations. It is found that the added mass coefficients are insensitive to the vibration amplitudes, while the added damping coefficients almost linearly increase with the amplitudes. Based on the added mass and damping coefficients, the vertical and torsional air-induced frequency reduction coefficients and aerodynamic damping ratios are calculated. Both the frequency reduction coefficients and aerodynamic damping ratios are closely related to deck configurations and model mass/mass moment of inertia, while independent of vibration frequencies. For the concerned six section models, the vertical and torsional frequency reduction coefficients are mainly located in the ranges of (1.0%, 2.5%) and (0.4%, 1.2%), respectively. The aerodynamic damping ratios are significantly dependent on the vibration amplitudes and may exceed the mechanical damping ratios for large amplitude cases. Based on numerical simulations, the mechanical frequency and damping ratio of a spring-suspended deck model can be identified by excluding the added mass and damping effects. • Weak-coupling method is adopted to simulate the free vibration of bridge decks in still air. • Windless-air-induced added mass and damping of six typical sections are numerically analyzed. • Windless-air-induced added mass and damping are respectively insensitive and sensitive to vibration amplitude. [ABSTRACT FROM AUTHOR]

The effective aerodynamic shape of a bridge deck during a buffeting response can be modified relative to its original section in the stationary state, and the identification method for aerodynamic admittance functions (AAFs) of a bridge deck considering the oscillation effect is established based on wind tunnel tests in conjunction with theoretical analyses. The aerodynamic forces on a bridge deck strip and surrounding fluctuating wind speeds, as well as the response of the model in a turbulent flow, are measured simultaneously on a stochastic vibrating spring-suspended sectional model (SSSM). A new method is proposed to separate the aerodynamic forces on the bridge deck strip into self-excited and buffeting force components. The AAFs with respect to longitudinal and vertical turbulence components are then identified according to the extracted buffeting forces and measured fluctuating wind speeds via a colligated least square method (CLSM). The approach is validated experimentally on a closed-box bridge deck strip using force-balance measurements, but it can be applied to bridge decks of any cross-section. The bridge deck AAF is confirmed to depend on its oscillation state, and the wind tunnel test for the identification of bridge deck AAFs was carried out in the oscillating state for high accuracy. • A new method of separating the aerodynamic forces on the bridge deck strip into self-excited and buffeting force components. • Direct identification method for aerodynamic admittance functions of a bridge deck considering the oscillation effect. • The bridge deck aerodynamic admittance functions is experimentally confirmed to depend on its oscillation state. [ABSTRACT FROM AUTHOR]

Tornado risks for highly important long-span bridges in tornado-prone regions can not be neglected. Rigid-model wind pressure measurements on a streamlined bridge deck were conducted using a tornado vortex simulator, to clarify tornado-induced surface pressure distributions, aerodynamic load coefficients and total force coefficients. We focused on two main parameters: swirl ratio and horizontal distance from tornado center to deck. Obvious discrepancies were observed between tornado-induced wind loading and results from conventional boundary-layer wind tunnels. Strip theory was not applicable since pressure distributions vary for different sections of the deck along the bridge axis. The absolute values of mean pressure coefficients for the deck section near tornado center are largest among all tested sections along the bridge axis. The most unfavorable mean sectional drag force coefficients were found when the bridge model is located at the tornado core radius and largest mean sectional lift force coefficients at the tornado center. With increase in swirl ratio, magnitudes of mean pressure coefficients as well as mean and fluctuating sectional aerodynamic load coefficients become smaller. The unfavorable locations for fluctuating rolling moment coefficients are different from those for mean values, which indicates that the quasi-steady assumption becomes invalid for tornado-induced rolling moment coefficients. Total force coefficients over the entire deck were investigated to evaluate the non-uniform loading characteristics. The findings will be helpful for predicting tornado-induced responses and risks for highly important long-span bridges. • Tornado-induced wind loads on a streamlined bridge deck was carried out. • The force coefficients are position-dependent and strip theory is not applicable. • Largest drag coefficients are at tornado radius and lift force at tornado center. • Magnitudes of pressure and force coefficients decrease with increase in swirl ratio. • Results are helpful for predicting tornado-induced responses and risks for bridges. [ABSTRACT FROM AUTHOR]

The post-flutter limit cycle oscillation (LCO) of a two-degree-of-freedom bridge deck involving aerodynamic nonlinearities is studied using computational fluid dynamics (CFD) simulations. To investigate the aerodynamic mechanism for the post-flutter LCO, a comprehensive energy budget analysis is conducted based on the simulated responses, in which the energy input properties of the 1st-order and higher-order force components are considered separately. Results show that only the 1st-order force components contribute significantly in the energy input, while the contributions of the higher-order force components are insignificant. The sensitivities of aerodynamic derivatives to vibration amplitudes and phase difference between vibration modes are investigated using forced vibration CFD simulations. For the concerned bridge deck, some aerodynamic derivatives are highly sensitive to vibration amplitude, while the influences of modal coupling effects are insignificant. A simplified multi-input multi-output nonlinear self-excited force model with amplitude-dependent aerodynamic derivatives is developed according to the sensitivity analysis. An example of bridge post-flutter LCO with two degrees of freedom is utilized to demonstrate the accuracy of the amplitude-dependent aerodynamic derivative-based model. The model also applies to single-degree-of-freedom LCOs, e.g., galloping and vortex-induced vibration, and hence it may serve as a unified analysis framework for nonlinear bridge aeroelasticity. [ABSTRACT FROM AUTHOR]

Numerical simulation of turbulent wind field is essential for the time-domain buffeting analysis of long-span bridges. However, recent field measurements captured strong non-stationary features during extreme wind events, which may pose questions on the current bridge aerodynamic analysis based on the stationary assumption. Therefore, it is both necessary and realistic to perform non-stationary simulation of turbulent wind fields of long-span bridges. In this study, a spectral-representation-based non-stationary process simulation algorithm, which takes advantage of the FFT technique, is proposed using non-negative matrix factorization. In addition, an appropriate scheme is recommended to search the initial matrices for the factorization. After factorizing the decomposed spectrum, the FFT technique can be utilized to enhance the non-stationary simulation efficiency. Numerical examples demonstrate the feasibility and effectiveness of the factorization of the decomposed spectrum. Then, the non-stationary turbulent wind field on the long-span bridge deck is simulated. The computational efficiency, accuracy and applicability of the proposed method are compared with alternative approaches. Results show that the factorization and simulation agree well with the target ones. Therefore, the proposed approach can be used to simulate the non-stationary turbulent wind field in practice. • A NMF-based SRM is proposed to simulate the non-stationary turbulent wind field of long-span bridge deck. • A Wavelet-based method is developed to find the initial matrices properly for the NMF of the decomposed EPSD. • The proposed NMF-assisted method is conducive to the non-stationary turbulent wind field simulation in practice. • Field measured EPSD is selected to simulate the non-stationary turbulent wind field of long-span bridge deck. [ABSTRACT FROM AUTHOR]

The problem of aerodynamic flutter has received much attention and continues to be important for slender structures, such as long-span suspension bridges. The wind flow across the structure can approximately be described as a two-dimensional flow across a moving flat plate, and the bridge motion can be expanded in heave and pitch motions, leading to the traditional aerodynamic derivatives description. In this paper, the classical Theodorsen model [NACA report no. 496, 1934] is revisited, and an extended method is proposed, allowing computation of the aerodynamic derivatives for more complex planar geometries, such as tandem configuration multi-deck bridges. In keeping with the Theodorsen model, the vorticity in the wake is modelled as a vortex sheet advected passively with the free-stream velocity. The bridge deck influence on the wind flow is described by a number of point vortices, and the aerodynamic forces and moments on the bridge are obtained as the rate-of-change of their aerodynamic impulse and angular impulse. Twin-deck bridges are considered for a number of inter-deck spacings. A set of critical reduced wind speeds, depending on the spacing between decks, are identified. Preliminary wind tunnel test results are reported and shown to correspond well to the point vortex model predictions. [ABSTRACT FROM AUTHOR]

Vortex-induced vibration (VIV) of deck girders frequently drives the wind-resistant design of wind-sensitive bridges from the preliminary to final design stages. Shaping bridge decks is a proven strategy to mitigate VIV. While significant shape modifications are commonly restricted to preliminary design stages, only minor medications are possible at advanced design stages, typically involving adding flow modifiers or changing the shape and location of existing appendages. These mitigation strategies have been implemented in the last decades by carrying out expensive wind tunnel campaigns and following heuristic design rules. This paper proposes an experimental data-driven adaptive surrogate-based optimization approach to systematically identify optimum deck shapes that minimizes the economic cost of the bridge while fulfilling the VIV project specifications. The methodology is conceived to carry out simultaneously the general and detailed shape design of the final deck configuration by harnessing a sequential sampling plan aiming at reducing the sectional model construction costs. The proposed holistic design framework is successfully applied to a real application case involving 26 wind tunnel tests of 1.8-meter wide sectional models to figure out the optimal gap distance and location of maintenance tracks of a twin-box deck equipped with all the appendages included in the final deck design. • A wind tunnel data-driven optimization method for shaping bridge decks is presented. • A Kriging surrogate is sequentially trained with data from 26 sectional model tests. • The gap distance and track position in a twin-box deck were holistically designed. • Vertical and torsional VIV were effectively mitigated, and the cost was minimized. [ABSTRACT FROM AUTHOR]

Large bridges' decks often exhibit different adhesion coefficients in complex environments, which are frequently accompanied by significant crosswind effects. This results in a complex and constantly changing flow field around vehicles, which can severely impact driving safety. In this study, the two-way coupling method is utilized to investigate the transient aerodynamic characteristics and dynamic response of vehicles passing through bridge towers at high speeds in different lanes with varied adhesion coefficients under crosswind conditions. The vehicle speed was 30 m/s, and the crosswind velocity was recorded at 11.33 m/s. The results indicate that the aerodynamic load fluctuates more significantly due to the influence of the bridge tower. In the same lane, the bridge deck with an adhesion coefficient of 0.4 produces a greater lateral displacement and yaw angle. When passing through the bridge tower, a vehicle in lane L1 is suddenly affected by vortex shedding, resulting in a larger lateral displacement and yaw angle compared to vehicles in L2 and L3 lanes. The lateral displacement measures 0.251 m, and the yaw angle measures 0.0205 radians at an adhesion coefficient of 0.4. This also indicates that driving in the L1 lane in a crosswind environment is relatively less safe. • A two-way coupling method is established. • The transient aerodynamic characteristic and dynamic response is investigated. • The high speed vehicle in different lane is considered. • Considering the effects of the adhesion coefficients. [ABSTRACT FROM AUTHOR]

With the increase of span length, long-span bridges become more flexible and susceptible to vortex-induced vibrations (VIV). Several models for vortex-induced force (VIF) and various methods for predicting VIV have been developed accordingly but without consensus. This paper uses the method of multiple scales, from a different angle of view, to analyze the general polynomial model for VIF and present a concise polynomial model for VIF and a simple method for predicting VIV of a bridge deck. The aeroelastic vibration of a deck section is simulated by the computational fluid dynamics (CFD) and the results are used to verify the concise polynomial model of VIF. The forced vibration of a deck section is also simulated by CFD to yield the simple method for predicting VIV together with the frequency response equation and the critical equation of VIV derived by the method of multiple scales. The results show that the even and cross terms of aerodynamic damping and stiffness in the general polynomial VIF model are small compared with the odd terms and can be thus omitted. The lock-in region and the amplitude of VIV of the deck section can be accurately predicted by the proposed simple method. • The method of multiple scales is used to analyze the general polynomial model for VIF on bridge deck section. • The frequency response equation and the critical equation of VIV are derived by the method of multiple scales. • The concise polynomial model for VIF is developed and verified through aeroelastic vibration simulation. • The simple method for predicting VIV of a bridge deck is developed in terms of the forced vibration simulation. • The lock-in region and the amplitude of VIV of the deck section can be accurately predicted by the proposed simple method. [ABSTRACT FROM AUTHOR]

This paper presents an experimental investigation of buffeting lift forces on a central-slotted box girder in turbulent flow, and aims to identify the corresponding generalized aerodynamic admittance (generalized-AAF) and two-dimensional aerodynamic admittance (2D-AAF). The generalized-AAF is obtained using the one-wavenumber spectra of lift and wind fluctuations, while the 2D-AAF is obtained using an improved method based on force-balance measurement. The key to this improved method is separating out the three-dimensional effect of turbulence (3D-effect) from the generalized-AAF while considering the segment length of the force measurement and turbulence integral scale. The results indicate that the generalized-AAF of the central-slotted box girder is much less than the Sears function, which is consistent with most previous studies. However, the values of 2D-AAF decay more slowly in comparison with the Sears function. An empirical formula for the 2D-AAF of the central-slotted box girder is given based on the experimental data. Additionally, the study finds that the ratio of the turbulent integral scale to the characteristic dimension of the model plays a significant role in determining the 3D-effect of turbulence, resulting in the difference between the generalized-AAF and 2D-AAF. Therefore, the 2D-AAF is particularly useful for estimating the buffeting force of a bridge deck when the turbulence scale does not match the size of the model. • An improved approach is proposed to determine the 2D-AAF of a central-slotted box girder in turbulent flow. • A dimensionless parametric analysis on the 3D-effect is conducted to reveal influence of scale parameters. • An empirical formula of the 2D-AAF of the central-slotted box girder is proposed. [ABSTRACT FROM AUTHOR]

Remote wind sensing technologies allow for measurements in a spatial domain beyond the one accessible by anemometers fixed to a mast. Remote optical wind sensors installed at an existing bridge site can both provide new information on the wind flow upstream of the bridge and capture the disturbed flow around the structure. These possibilities are explored in the presented measurement campaign with three synchronised continuous-wave Doppler lidars at the Lysefjord bridge in Norway. In particular, the interaction between the oncoming wind flow and the bridge deck is studied in terms of the mean velocity deficit wake profile as well as the spectral turbulence characteristics. The lidar measurements are validated by comparing the lidar observations at locations undisturbed by the structure with corresponding sonic anemometer data recorded 6 m and 10 m above the deck. The consistency between the two sets of data is tested in terms of the turbulence time series, their spectral content and the statistical moments. Within the wake of the bridge, significant values of vertical velocity and inclination angles, as well as turbulence intensities are seen. Moreover, the wake region can be distinguished by its singular spectral content, cross-correlation coefficient, and coherence. The results show that the tailored configuration of the lidars succeeded in providing information on 3D turbulence around the bridge, thereby capturing the bridge aerodynamic characteristics in full-scale. [ABSTRACT FROM AUTHOR]

This work focuses on the effect that the angle of incidence of the wind has on the flow around bridge decks with low-rise edge parapets, and how it affects the aerodynamic actions on vehicles. First, a generic deck model with different barrier configurations is studied using computational fluid dynamic (CFD) analysis, and it is observed that for very skew winds even relatively low barriers can deviate the flow to make it aligned with the direction of the deck, which is referred to as channelling effect in this study. The work continues with an extensive wind tunnel (WT) testing programme on a deck model that represents a realistic bridge with a conventional configuration of short side barriers. The flow visualisation and the aerodynamic forces measured on a high-sided vehicle show the existence of three different zones in terms of the skew angle of the wind, which are in agreement with the CFD results. It is concluded that skew winds can significantly increase the aerodynamic actions on the vehicles due to the reduction of the shielding area across the width of the deck, and also because of the along-deck wind channelling. • Detailed study on the wind flow around bridges with solid parapets. • CFD analysis of the along-deck flow channelling effects in bridges under skew winds. • Wind tunnel testing of aerodynamic forces on vehicles at different positions of the deck. • Novel response parameters are proposed to study the observed channelling effects. • Flow visualisation techniques are used describe the influence of the skew angle. [ABSTRACT FROM AUTHOR]

Abstract The windless-air-induced added mass/mass moment of inertia (m a / I a) and damping (c a) effects on mechanical parameters of a vibrating bridge deck are usually ignored in wind tunnel tests. In this paper, for three typical deck sections, computational fluid dynamics simulations are carried out to study the vertical/torsional single degree-of-freedom forced vibration under windless conditions, and further to reveal the effects of m a , I a , and c a on the modal parameters. The influences of turbulence model, computational domain size, grid resolution, and time step size are analyzed. For the addressed issue, the Reynolds stress equation model (RSM) is found to be more suitable than the shear stress transportation (SST) k - ω model. A mathematical model for aerodynamic forces at zero wind speed is presented by using the dimensionless m a , I a , and c a , and they can be extracted by combining the motions and the numerically simulated aerodynamic forces using the least squares method. The numerically simulated results for an ideal plate under small amplitudes are very close to the theoretical values, and consequently verify their accuracy. The causes for the non-zero values of flutter derivatives H 4 ∗ and A 3 ∗ at zero wind speed are revealed. In the windless air, the added damping almost linearly increases with the vibration amplitude. Five existing long-span bridge deck models are taken as examples to investigate the effects of m a , I a , and c a on structural frequencies and damping ratios. Highlights • The CFD simulation is used to comprehensively study the bridge added mass and damping in windless air. • Compared to SST k-w, RSM turbulence model is verified to be more appropriate for the addressed issue. • The simulation accuracy is validated by using a thin plate with theoretical values. • The causes for the non-zero flutter derivatives H 4 ∗ and A 3 ∗ at zero wind speed are revealed. [ABSTRACT FROM AUTHOR]

Considered to be representative of a generic bridge deck geometry and characterised by a highly unsteady flow field, the 5:1 rectangular cylinder has been the main case study in a number of studies including the “Benchmark on the Aerodynamics of a Rectangular 5:1 Cylinder” (BARC). There are still a number of limitations in the knowledge of (i) the mechanism of the vortex-induced vibration (VIV) and (ii) of the turbulence-induced effect for this particular geometry. Extended computational and wind tunnel studies were therefore conducted by the authors to address these issues. This paper primarily describes wind tunnel and computational studies using a sectional model in an attempt to bring more insight into Point (i). By analysing the distribution and correlation of the surface pressure around an elastically mounted 5:1 rectangular cylinders in smooth and turbulent flow, it revealed that the VIV was triggered by the motion-induced leading-edge vortex; a strongly correlated flow feature close to the trailing edge was then responsible for an increase in the structural response. [ABSTRACT FROM AUTHOR]

As Storm Tor struck the western coast of Norway, wind speeds and bridge deck accelerations along the Hardanger Bridge girder were recorded by the monitoring system installed on the bridge. Using 13.5 h of data, mean wind speed, turbulence intensities, gust factor, turbulence length scales, angle-of-attack, and one-point and two-point turbulence spectra are studied using 10-minute stationary averaging intervals. Using the measured turbulence statistics as inputs, the buffeting response of the bridge deck is calculated in the frequency domain. The calculated response is compared with the measured response in terms of the root-mean-square (RMS) of acceleration and displacement components and the power spectral density of the acceleration response. Significant discrepancies are found in the case of the vertical response. Predicting the spectral response is found to be more difficult than predicting the RMS response, in particular for high-frequency responses. Considering the spanwise non-uniformity of turbulence statistics did not affect the predictions significantly. [ABSTRACT FROM AUTHOR]

Stress-level buffeting analysis is necessary for evaluating stress-related performance and safety of long-span bridges. A stress-level buffeting analysis requires knowledge of characteristics of distributed aerodynamic pressures on a bridge deck. This paper, therefore, presents a framework for modelling distributed aerodynamic pressures on the surfaces of a bridge deck in terms of the proper orthogonal decomposition (POD) method. The characteristics of aerodynamic pressure modes, such as covariance modes, principal coordinates, pressure modal coefficients, and pressure modal admittance functions are introduced in the formulation. Wind tunnel pressure tests of a sectional motionless deck model were conducted to identify the characteristics of distributed aerodynamic pressures on a twin-box bridge deck as a case study. The pressure modal admittance functions were identified by using a colligated least-square method. The results show that the higher-order POD pressure modes provide a very limited contribution to the aerodynamic pressures and can be truncated without notable loss of accuracy. The aerodynamic pressures distributed over the bridge deck surface can be well represented by a superposition of a limited number of POD pressure modes that include the first two pressure modes. The use of pressure modal admittance functions greatly simplifies the identification of many individual aerodynamic pressure admittance functions. [ABSTRACT FROM AUTHOR]

With the increase of span length, long-span bridges become more flexible and susceptible to vortex-induced vibrations (VIV). Large-amplitude VIV may cause fatigue damage to structural components, and therefore accurate predictions of vortex-induced responses (VIR) are important. This paper proposes a mode-by-mode VIV analysis method for long-span bridges with twin-box decks under non-uniformly distributed turbulent winds. A semi-empirical model of vortex-induced forces (VIF), developed by the authors and validated by direct force measurements on an elastically-mounted twin-box section model under turbulent winds, is embedded in the VIV analysis method. The proposed analysis method is then used to analyze the VIV of a real long-span suspension bridge of a twin-box deck. The computed VIR of the prototype-bridge is finally compared with the VIR measured on-site by a structural heath monitoring system installed in the bridge. The comparative results show that the proposed VIV analysis method can be used to predict the VIR of long-span bridges with twin-box decks. Further studies also show that the non-uniform distribution of mean wind speed reduces the VIV of the bridge. Turbulence also diminishes the VIV of the bridge, and the reduction effect is larger on lower-order modes of vibration than on higher-order modes of vibration. [ABSTRACT FROM AUTHOR]

A numerical simulation technique based on computational fluid dynamics (CFD) for determining the time-varying histories of free vibration displacements, velocities, and aerodynamic forces of bridge decks is presented. The weak coupling method is used to address the problem of fluid-structure-interaction (FSI). The flutter derivatives can be conveniently extracted using the numerically simulated displacements, velocities, and aerodynamic forces, which is similar to the procedure adopted in the forced vibration method. First, the identification accuracy of flutter derivatives is validated by comparison with the theoretical results for an ideal thin plate. Then, the flutter derivatives of two typical bridge deck sections, one streamlined and one bluff, are extracted by the proposed method. The results of the streamlined section show good agreement with other methods. However, for the bluff section, noticeable discrepancies exist between different methods. The mean angle of incidence in the free vibration method is shown to be responsible for these disagreements. The strengths of the newly-proposed approach are compared with those of the numerical and experimental forced vibration and experimental free vibration methods. This convenient and effective approach may serve as a building block for extracting flutter derivatives and better understanding of the aeroelastic responses of long-span flexible bridges. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The quality of aeroelastic tests of long-span bridges is highly influenced by the ability of the reduced-scale models to reproduce the dynamic response of the real bridge. Hence, the design of the models is one important component in the process, as differences between the dynamic properties of the model and the prototype typically arise due to inherent limitations when constructing the reduced-scale model. This paper reviews the design process of full bridge reduced-scale models and explores sources of inaccuracies. A method based on optimization algorithms is proposed to reduce these inaccuracies in the model dynamic responses. This method is applied to a modified version of a real project consisting of a cable-stayed bridge with two diamond-shaped towers, single-box deck, 176 stays, and four piers. The optimization of the dynamic properties of the full bridge reduced-scale model is conducted in two phases: the first one optimizes the standalone tower, and the second one the complete bridge model. The results show the capabilities of the method, which nearly eliminates the inaccuracies in the natural frequencies of the model. The effects on other dynamic properties, such as variations in the generalized masses and in the modal shapes, are studied and commented upon. [ABSTRACT FROM AUTHOR]

Coupled vibration of the wind-vehicle-bridge system is an important research to ensure the safety and comfort of the vehicles running on bridges in crosswinds. The aerodynamic characteristics of the vehicle-bridge system are fundamental. The wind tunnel experiment is the first choice to study the aerodynamics of the vehicle-bridge system. But the sizes of the general wind tunnels are limited, the scaled model may bring out Reynolds number effects. The realized moving speeds of the vehicles in the boundary wind tunnel are very low. The special wind induced by the moving vehicles may not be explored fully. Therefore, Computational Fluid Dynamics (CFD) has become the alternate tool to explore the aerodynamic characteristics of the vehicle-bridge system. In this paper, the aerodynamic studies of vehicle-bridge system based on CFD were reviewed to provide a systematic summary, including the basic stationary system, the moving vehicle on the bridge deck, the shielding effects of the bridge tower, the protection of the wind fence, and the complex surroundings. The validation results of the simulations are very convinced. Through this review, the confidence of using CFD to explore the aerodynamic characteristics of vehicle-bridge system is established. Some comments and future trends are also discussed. • A full review of the aerodynamic characteristics study of vehicle-bridge based on computational fluid dynamics is given. • The confidence of using CFD to explore the aerodynamic characteristics of vehicle-bridge system is established. • Summaries of previous researches and suggestions for future research trends are provided. [ABSTRACT FROM AUTHOR]

A new experimental set-up with an active turbulence grid for wind tunnel testing of bridge decks in homogeneous freestream turbulence is presented. Unlike other active turbulence generators applied in bridge aerodynamics, the active turbulence grid generates stochastic turbulence and not quasi-harmonic velocity fluctuations that are correlated along the section model. A twin deck and a single deck section model are tested for aerodynamic properties using different incoming turbulence. The results show that the static coefficients can be highly sensitive to the properties of the incoming turbulence and that the sensitivity varies between the tested cross-sections. Significant changes in aerodynamic derivatives were observed with changing turbulence properties. The turbulence-dependent changes in the aerodynamic derivatives are less clear compared to the static coefficients since the presence of turbulence and buffeting forces makes it more difficult to identify the aerodynamic derivatives. It is also clear that the turbulence creates large variations in the instantaneous angles of attack, questioning the validity of linear models for prediction of self-excited forces. It is concluded that the active turbulence grid is a valuable asset in bridge aerodynamics research as it allows for novel studies of bridge aerodynamic properties in conditions relevant to long span bridge design. • A new active turbulence grid is presented. • Reynolds number dependency of force coefficients shown to fade as turbulence increases. • Drag coefficient of single deck was seen to be about 20% lower in turbulent flow. • Nonlinear behavior of single deck static coefficients is shown to fade in turbulent flow. • Change in twin deck A 2 * with increased turbulence. [ABSTRACT FROM AUTHOR]

In order to investigate the effect of wind non-uniform characteristics in mountainous terrain on the dynamic analysis of a vehicle-bridge (VB) system, a typical bridge site for a terrain model was established in a wind tunnel. Six typical flow directions, such as parallel to the river direction and perpendicular to bridge axis and ridge, were adopted to study the mean wind speed of experimental monitoring points at the bridge deck. Owing to the local ridge at the bridge site, the distribution of wind speed along the bridge deck shows obvious non-uniform characteristics. Seven monitoring points were set on the bridge deck, and the linear interpolation method was adopted to obtain the time histories of the wind speed at every point. A scaled wind tunnel model was also applied to conduct the three aerodynamic coefficients of the vehicle and bridge. Based on the experimental wind characteristics of mountainous terrain, the numerical framework of the wind-vehicle-bridge (WVB) system was established considering the effect of non-uniform wind, where a railway cable-stayed bridge was simulated using the finite element model, and a multi-body dynamic model of the vehicle was used. The influence of fluctuating wind excitation on the WVB system was discussed, and it played an essential role in vehicle vibration. • The non-uniform characteristics of wind field in the mountain area are investigated in the wind tunnel. • Based on the conducted results, the safety of vehicle moving through the bridge is studied. • With or without fluctuating wind excitation, the dynamic responses of vehicle-bridge system are also computed. [ABSTRACT FROM AUTHOR]

Permeable surfaces are extremely common in applications, ranging from wind shields installed on bridge decks to the outer layer of permeable double skin facades. However, due to the large scale separation between the overall dimensions of the structure and the size of the pores, their modelling in Computational Fluid Dynamics, CFD, simulations are still extremely problematic. In particular, explicitly modelling the pores geometry leads to prohibitive computational costs, while homogenized models based on the use of so-called pressure-jumps are often very crude simplifications of their aerodynamic behaviour. In this paper, a novel approach based on the use of pressure–velocity jumps, PVJ , is proposed. Firstly, the approach is deduced in a general form, based on mass and momentum conservation across the permeable surface. Then, some limit cases for which an analytical evaluation of the coefficients characterizing the model can be obtained are discussed. Finally, a ground mounted barrier is modelled, considering permeable surfaces of widely different aerodynamic behaviour. Results obtained modelling the barrier geometrical details and using the proposed PVJ approach are compared, confirming the soundness of the proposed approach. An OpenFOAM boundary condition implementing the proposed method is available at https://site.unibo.it/cwe-lamc/en. • A novel approach for the CFD modelling of permeable surfaces is proposed. • The approach is based on pressure and tangential velocity jumps. • The approach accounts for both normal and tangential forces. • Results are compared to those obtained for the detailed permeable surface geometry. [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]

Accurately identifying the aerodynamic loads on vehicles is the fundamental issue for assessing the driving safety of vehicles on long-span bridges subjected to strong crosswinds. Thus, the aerodynamic interference of bridges with vehicles must be considered. However, very few studies have been conducted to quantify both the steady and unsteady crosswind loads for vehicles on wide bridge decks. In this paper, the mean and peak aerodynamic coefficients and aerodynamic admittance functions for three types of high-sided vehicles (medium trucks, buses, and tractor-trailers) on two wide bridge decks (a single-box girder and a twin-box girder) were determined by means of wind tunnel tests. The effects of vehicle position, wind angle of attack, and geometric shape of the deck on these aerodynamic parameters were investigated. The results show that the aerodynamic coefficients of vehicles on both bridge decks vary significantly with their lateral position. Moreover, the effect of wind angle of attack on the aerodynamic coefficients of vehicles on the leeward side of the twin-box girder is extremely substantial, as is the geometric shape of the bridge deck. However, the vehicle position, wind angle of attack, and bridge deck geometry all have little influence on the aerodynamic admittance functions of vehicles. • Various cases on steady and unsteady aerodynamic forces of vehicles on two wide bridge decks under crosswind are studied. • Bridge deck geometry, vehicle position and wind angle of attack have significant effects on aerodynamic parameters of vehicles on bridge decks. • Empirical expressions of aerodynamic admittance functions of vehicles on wide bridge decks are fitted. [ABSTRACT FROM AUTHOR]

Pressure measurement experiments were carried out on three streamlined box girders with three geometric ratios of 1:50, 1:75 and 1:100 in five turbulent flow fields generated by grids. The turbulence intensities only affected the root-mean-square (RMS) of the pressure coefficients in the flow separation zone, while the turbulence integral scales affected the RMS of the pressure coefficients over the entire cross-sections. The spanwise correlations of the fluctuating winds and buffeting forces mainly varied with the turbulence integral scales. New strategies are proposed to identify the two-dimensional aerodynamic admittance functions (2D AAFs) using the two-wavenumber approach. The two-wavenumber coherence functions of fluctuating winds or buffeting forces obtained through new strategies do not need to use the empirical spanwise root-coherence function models compared to the traditional strategy. A complete analysis of 2D AAFs based on different strategies was performed. The determined 2D AAF using spanwise root-coherence function models varied with the kinds of spanwise root-coherence function model and relied on spacings chosen to fit, which caused the 2D AAF to vary in size. Therefore, the strategy without any spanwise root-coherence function models is recommended, and it is confirmed to give reliable and repeatable bridge deck 2D AAFs. • The new strategy is proposed to reliably and repeatably identify the 2D AAFs of a bridge deck. • The 2D AAFs obtained by different strategies are compared. • The misunderstanding regarding the two-wavenumber coherence function model is clarified. • The advantage only considering the normalized co-spectrum in the recommended strategy is explained. [ABSTRACT FROM AUTHOR]

Steel–concrete composite bridge decks may risk galloping instability during their bridge-launching phase, since the normally first launched steel boxes could feature bluff and lightweight cross section. In our previous study, a bridge deck of open cross section (typically used in steel–concrete composite bridges) has been found in smooth flow highly prone to the unsteady galloping instability occurring at relatively low reduced wind speed. Considering the natural wind field is usually turbulent, motivations arise to understand what role can the incident turbulence play in the galloping instability of this open cross section deck. New wind tunnel tests were therefore carried out in grid-generated turbulent flow, characterized by an integral length scale comparable to the bridge deck height and an intensity of 9% to 15%. For the interested wind angles of attack around null, static tests first indicate the incident turbulence is able to promote an even higher galloping factor than that in smooth flow, while the Strouhal number shows a decrease. This suggests a higher proneness for the galloping and vortex induced vibration to interact. In aeroelastic tests, however, the typical unsteady galloping instability due to the interaction with vortex induced vibration has never been observed. Instead, the unsteady galloping is initiated in a more complicated manner: unrestricted oscillation arises at a reduced wind speed clearly higher than the Kármán-vortex resonance one even for a very low Scruton number (the mass-damping parameter), combined with the absence of any Kármán-vortex excitation. Nevertheless, similar to the smooth flow condition, the nosed-up 4° remains to be the most unfavorable wind angle of attack in turbulent flow, featuring the lowest galloping onset in the low Scruton number condition. Finally, dependent on the magnitude of Scruton number, it is able to conclude that the incident turbulence can either suppress or promote the galloping instability of this bridge deck. • A bridge deck typical for steel–concrete composite bridges in the construction phase. • The bridge deck can gallop in turbulent flow of an intensity not lower than 15%. • Quasi-steady theory may predict unconservative onset even at high Scruton number. • Dependent on Scruton number, turbulence can either suppress or promote galloping. [ABSTRACT FROM AUTHOR]

In conventional buffeting analyses for long-span bridges, the aerodynamic admittance functions (AAF) with respect to the longitudinal (u-) and vertical (w-) turbulence components are usually assumed to be equivalent. This assumption could cause unpredictable errors due to complicated turbulence-structure interactions. This study proposes an experimental method to determine the u- and w- AAFs in the framework of three-dimensional buffeting theory. First, passive wind tunnel test is conducted to measure necessary aerodynamic parameters. Next, the turbulence characterized only by u-velocity fluctuations is generated in a multi-fan active-controlled wind tunnel to reproduce the u-velocity component in the passive wind tunnel test. The aim is to identify the u-AAF separately. Finally, the w-AAF is evaluated by combining the parameters measured in the active and passive wind tunnel tests. For a streamlined bridge girder, results show significant discrepancies between the u-AAF and w-AAF. The derivation degrees depend on the frequency and the angle of attack (AoA). This indicates the inaccuracy of the conventionally invoked assumption. In detail, the w-AAF is higher than the u-AAF at low frequencies, whereas the relationship reverses at higher frequencies. The proposed method is also applicable for other bluff-body structures, it is useful for improving the accuracy of buffeting analyses. [Display omitted] • A theoretical framework is derived to determine the AAFs with respect to u- and w-turbulence components. • The three-dimensional effects of turbulence are considered in the theoretical framework. • The theoretical framework is realized by combining active- and passive-wind tunnel tests. • The u-component in the active-wind tunnel test is adjusted to reproduce that in the passive wind tunnel test. • Comparisons between the u- and w-AAFs of a bridge deck directly indicate the inaccuracy of the equivalent-AAF assumption. [ABSTRACT FROM AUTHOR]

A new procedure to assess the crosswind hazard of operating a vehicle over a bridge deck has been developed using a probabilistic approach that utilizes long-term wind data at bridge sites as well as the aerodynamic properties of bridge decks and vehicles. The proposed procedure for safety assessment considers the probabilities of two accident types: sideslip and overturning. The vulnerability of vehicles to crosswinds is represented by the number of days for traffic control that would be required to secure vehicle safety over a period of one year. The distribution of wind speed over a bridge deck was estimated from a section model wind tunnel test. A sea-crossing bridge was selected as an example, and a series of case studies were performed to identify the influential factors affecting vehicle vulnerability to crosswinds: vehicle type and loaded weight, the position of a running vehicle over a bridge deck, the bridge alignment relative to the dominant wind direction, and vehicle speed. [ABSTRACT FROM AUTHOR]

A detailed wind tunnel test has been carried out on a motionless flat-box bridge deck model with three special grid-generated wind fields using an electronically scanned pressure transducer system, enabling almost instantaneous capture of 372 pressure tap signals from 6 sections of 62 different spacing taps at each section. A very complete analysis has been performed on the pressure signals, and fluctuating forces through weighted integrations of pressure at each section were formed. The integral scales of fluctuating force were found to be dependent mainly on the integral scale of turbulence and the size of deck. The root coherence of buffeting force relied chiefly on integral scales of force and the separation of two sections, and the span-wise correlation of the fluctuating forces were larger than those of wind turbulence. An empirical model of root coherence for the fluctuating lift for a flat-box deck has been developed and proved to be feasible and effective for fitting the test data. The fitted parameters can be defined by simple expressions related to the oncoming turbulence and the size of deck, and thus it has practical applications. The proposed model can fully explain the character of low frequency curves in the root coherence. [ABSTRACT FROM AUTHOR]

The susceptibility of bridge decks to vortex induced oscillations can be addressed through wind-tunnel testing. This paper considers the case of the Vila-Real Bridge, in the north of Portugal, which has the highest deck above ground (230 m), among concrete-deck bridges cable-stayed in the central plane. It has a single-cell rectangular box girder with a wide top flange supported by regularly spaced inclined struts. Aeroelastic studies of this precise type of deck seem nonexistent in the literature. Results of sectional model tests are presented for a selection of three distinct angles of attack and three deck configurations, including a solution, alternative to the usual mitigation measures, that solved the susceptibility to vortex induced vibration of the deck and that has no relevant additional design or building costs. With the proposed approach, bridge designers may be able to relegate the use of sections with high aerodynamic performance – but that can be more costly, pose a greater challenge in the construction, or require more time to completion – and the use of mitigation measures, to cases in which they prove to be absolutely necessary. [ABSTRACT FROM AUTHOR]

Polynomial-type empirical models have been commonly adopted to describe the vortex-induced force (VIF) on bridge decks in the study of vortex-induced vibration. Previous studies chose different nonlinear damping terms like the Van der Pol or Rayleigh type in such models without explaining whether these same-order terms can be chosen arbitrarily. A novel parameter identification technique is developed in this paper to distinguish different same-order nonlinear terms in the VIF model with additional governing equations based on the orthogonality among motion-induced terms. The parameter identification results obtained from the wind-tunnel tests on a central-slotted box deck indicate that the Rayleigh-type damping terms are the only important ones in the vertical VIF, whilst none of the same-order nonlinear damping terms of the torsional VIF should be ignored. The finding is then theoretically explained assuming that the aerodynamic damping nonlinearity of VIF primarily comes from the continuous change of relative attack angle between the oscillating deck and the incoming wind. • New parameter-identification method to distinguish same-order terms in polynomial-type VIF model. • Reason why different models should be used for vortex-induced vertical and torsional forces. • An accurate reproduction of the VIF spectrum achieved by using the proposed method [ABSTRACT FROM AUTHOR]

The Π-shaped bridge deck may easily occur vertical vortex-induced vibration, due to the bluff body aerodynamic configuration, which may cause the uncomforting of vehicles and pedestrians on the bridges. The present study mainly focused on the two "lock-in" regions characteristics of vertical vortex-induced vibration (VIV) of Π-shaped bridge deck, which can reveal the aerodynamic mechanism of vibration mitigation countermeasures. The vertical VIV response of original Π-shaped deck and those with different countermeasures are experimentally investigated detailly. Computational fluid dynamics (CFD) method is employed to numerically simulate the surrounding flow field of original girder section and those with different aerodynamic countermeasures. The numerical method is firstly verified through the comparison with the results of corresponding experimental results obtained in wind tunnel test. Afterwards, the flow pattern and vortex structure around the girder section simulated by CFD are utilized to interpret the effects of the mitigation countermeasures. The numerical results show that: (a)The vibration mitigation effect in the first vortex "lock-in" region is not sensitive to the position of the aerodynamic countermeasures, while the vibration mitigation effect in the second "lock-in" region is more sensitive to the position of the aerodynamic countermeasures; (b) The phase of aerodynamic lift and displacement response is close to synchronization in the ascending section of the VIV amplitude, greater than 90 ° in the descending section, and close to 180 ° outside the vortex-induced resonance range. The first vertical VIV region is related to the "Karman vortex street" at the trailing edge of the section, while the second vertical VIV region is related to the vortex shedding at the lower edge of the front end of the section and the secondary vortices on the upper surface. • The aerodynamic mechanism of mitigation countermeasures on Π-shaped bridge deck was systemically investigated. • The vibration mitigation effect in the second "lock-in" region is more sensitive to the position of the aerodynamic countermeasures. • The phase of aerodynamic lift and displacement response is discussed in different vortex-induced resonance region. [ABSTRACT FROM AUTHOR]

Long-span rail-cum-road bridges with twin separated parallel decks have become a recommended structural form because of their superior traffic capacity. However, because of inconsistent dynamic characteristics of highway and railway bridges, different wake characteristics and special aerodynamic interference between the asymmetric twin decks, the vortex-induced vibration (VIV) characteristics for twin-deck bridges are more complicated. In this paper, wind tunnel tests were carried out to study the VIV characteristics of a long-span rail-cum-road bridge with twin separated parallel decks. Furthermore, fluctuating wind pressure of the highway and railway girders was measured to discuss the vibration phenomenon. The results indicated that the VIV of the railway girder only occurs upstream, while the VIV of the highway girder occurs both upstream and downstream. The aerodynamic interference has an impact on the VIV response of both upstream and downstream girders. 3° is still the most unfavorable wind incidence angle for the twin parallel deck bridges. Increasing structural damping helps to suppress VIV, but it cannot completely suppress the occurrence of VIV. Adjusting the wind fairing angle of the highway girder and sealing the handrail at intervals are both effective in controlling VIV, but the effects are different for upstream and down girders. For the twin separated parallel decks bridges, the VIV suppression effect of the aerodynamic measures needs to be comprehensively considered from the overall consideration of the twin decks under different incoming flow directions. • Vortex-induced vibration (VIV) and VIV-suppress measures for a rail-cum-road bridge are investigated in wind tunnel tests. • Necessity of considering the aerodynamic interference and direction of incoming flow of rail-cum-road bridges is highlighted. • The VIV suppression effect needs to comprehensively considered both twin girders under different incoming flow directions. [ABSTRACT FROM AUTHOR]

Tropical cyclones landing on the coast are usually associated with both strong winds and waves, posing a major threat to sea-crossing bridges. Strong waves riding on the elevated storm surge squeeze the narrow gap between the sea surface and bottom of the bridge deck, thus complicating the wind field and leading to different bridge nonlinear flutter responses as compared with the steady flow field. In this study, to evaluate the bridge safety under such circumstances, wind tunnel test was carried out for a typical sea-crossing bridge with streamlined box girder based on a developed dynamic response test system for simulating the coupling effect of wind, wave, and current on bridges, where the clearance, underneath the bridge deck, and wave speed can be systematically adjusted to investigate the wind field characteristics and bridge nonlinear flutter response. Numerical simulation with the LES (large eddy simulation) scheme was employed to successfully visualize the wind field around the bridge and the mechanism of the nonlinear flutter response was analyzed in detail. The results of this preliminary investigation show that: (a) In the wind tunnel tests, when the wave crest passes under the bridge, the acceleration effect due to the narrow gap can lead to an increase for the nonlinear flutter amplitude of the bridge, which threatens the structural safety; (b) The measured wind speed at the bridge site exhibits strong turbulence intensity and non-Gaussian distribution tendency; and (c) Based on the numerical simulation, the airflow between the wave crest and the main structure features a large vertical velocity component, leading to a large AOA (angle of attack) value of the incoming flow. Meanwhile, the air pressure around the girder is unevenly distributed, thus unavoidably weakening the aerodynamic stability of the bridge. • The non-linear bridge flutter stability is analyzed by simulating the wave-interfered wind field in the wind tunnel test. • Wave-interfered wind field characteristics are studied experimentally and numerically. • The bridge non-linear flutter response is closely related to the spatial relationship of wave and bridge. [ABSTRACT FROM AUTHOR]