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As the number of long-span bridges continues to grow, wind-induced vibration issues have become increasingly intensified. Among them, flutter is a serious wind-induced vibration that can lead to bridge collapse. To address this problem, this paper proposes inerter-based dampers as a solution for flutter control and compares their performance to traditional tuned mass dampers (TMDs). Firstly, eight distinct inerter-based dampers were proposed, based on various combinations of mass-inerter-spring-damper (MISD) components. Secondly, the equations of motion of the bridge-MISD system were derived based on the two-mode coupled flutter theory and the mechanical impedance analysis method. Thirdly, the flutter control performance of the eight proposed MISDs is examined using a simply supported beam, with the six better-performing dampers further evaluated using the Jiangyin Bridge. The results show that inerter-based dampers can effectively improve the critical flutter wind speed of bridges, with performance sensitive to frequency. Additionally, incorporating an inerter decreases the static displacement of the mass block, while increasing the mass of MISD and the distance between the damper and the section center improves flutter control performance. The optimal spring stiffness ratios for the six MISDs are identified, largely dependent on the damper's inertance and mass. In conclusion, this paper offers a promising solution to addressing flutter in long-span bridges and provides insights into the design and optimization of inerter-based dampers. [ABSTRACT FROM AUTHOR]

Wind loads play an important role in the design and construction of long-span bridges, especially for that built in mountain valley, and wind characteristics in mountain terrain are still unclear. To further understand the wind characteristics at a bridge site in a mountain valley, large eddy simulations were employed to comprehensively study the wind characteristics at the bridge site in an L-shaped canyon. Different wind directions consisting of 0°, 45°, 90°, 135°, 180°, 225°, 270°, and 315° were considered, and the wind characteristics on the main girder and towers, as well as the flow field, were comprehensively investigated. The results indicate that the mean and fluctuating wind characteristics are significantly different from those specified in the relevant specifications, and it is inappropriate to apply the specifications directly to mountainous terrain. When wind flows along a channel, it leads to a large wind speed amplification factor, strong non-Gaussianity, and large kurtosis and skewness. The steeper the slope of the mountain, the stronger the non-Gaussianity of the fluctuating wind. The coherence function remains nearly unchanged when the distance between the two points is constant, regardless of the location. The wind characteristics at the main girder and towers are so different that they should be considered separately and taken into account in engineering practice. This study provides a reference for the wind-resistant design of bridges and structures built on mountainous terrains. [ABSTRACT FROM AUTHOR]

The accurate characterization of offshore wind resources is crucial for the efficient design and operation of wind energy projects. However, the scarcity of in situ observation in marine environments requires exploration of alternative approaches. For this reason, this study presents a comprehensive comparison between wind profiles derived from the Advanced Scatterometer ASCAT) satellite observations and the ERA5 reanalysis dataset against ship-based lidar measurements in the Northern Baltic Sea. In order to extrapolate ASCAT observations to wind turbine relevant heights, a long-term correction approach has been implemented. Due to the sensitivity of this method to the accurate characterization of the atmospheric stability, two different approaches were assessed to characterize the stability conditions, showing a great robustness of the methodology employed and leading to noticeable differences only in specific coastal locations. The comparison reveals a close agreement between ASCAT and ERA5 beyond 40 km distance from the coast. Specifically, ASCAT tends to overestimate the mean wind speed derived from lidar measurements, while ERA5 exhibits a consistent underestimation. In terms of vertical accuracy, ERA5 displays a consistent bias of approximately 0.5 m s-1 along the profile, whereas ASCAT exhibits a smaller bias within the lower 200 m of the profile. These findings underline the potential and limitations of ASCAT-derived wind profiles and ERA5 for offshore wind characterization. [ABSTRACT FROM AUTHOR]

The present paper combined the natural environment excitation technology (NExT) with the eigen system realization algorithm (ERA) to identify the modal parameters of a suspension bridge. Firstly, the critical parameters in NExt–ERA, such as record length, window length, and ranks of the Hankel matrix, and their influence on identification accuracy have been discussed. Subsequently, based on the acceleration series obtained from the Xihoumen Bridge Health Monitoring System, 3015 sets of modal frequencies and modal damping ratios of the Xihoumen Bridge were identified under 7 sets of wind speeds by the NExt–ERA. Finally, the probability distribution and confidence interval of the structural modal damping ratios were analyzed. Besides, the dependence of identified frequencies damping ratios on wind speed was also discussed. The results show that at the same wind speed, the mean value, and variance of the torsional and lateral mode damping ratios are larger than those of the vertical mode, but this difference gradually decreases with the increment of wind speed. The modal damping ratios along three directions under different wind speeds all follow the generalized extreme value distribution, but wind speed affects the tailing properties of probability distribution of the vertical and torsional mode damping ratios. The estimated damping ratios could provide references for structural design and vibration control of similar long-span bridges. [ABSTRACT FROM AUTHOR]

Wind-induced vibration has become increasingly prominent for long-span bridges. Flutter instability, as a type of divergent vibration, is a key component in the wind resistance investigation of long-span bridges. Based on the principle of instantaneous power balance (IPB) of the flutter critical state of bridge girders, an algorithm for predicting the flutter critical wind speed of long-span bridges was proposed by utilizing a nonlinear optimization strategy. For the bending–torsional coupling two-dimensional (2-D) motion system, the contribution of the wind-induced self-excited and structural elastic forces of the 2-D bridge section to the energy of the system was revealed to be dependent on some key parameters, such as reduced frequency, wind speed, amplitude ratio, and phase lag between vertical and torsional motions. Therefore, according to the principle of IPB during the critical flutter state, the prediction of flutter onset wind velocity can be transformed into an extreme value optimization problem of the IPB objective function. The feasibility and accuracy of the IPB algorithm were verified by comparing them with those obtained from segmental model wind tunnel tests and previous 2-D flutter prediction algorithms. Compared with the traditional methods characterized by force balance, the proposed method clearly and quantitatively presents the contribution relationship among multiple self-excited aerodynamic components on the flat plate and bridge section while flutter occurs; the method first evaluates the flutter critical state as an alternative algorithm from an energy perspective. [ABSTRACT FROM AUTHOR]

Crosswind is the primary external excitation source of the straddle monorail system. To ensure the ride quality of the monorail system under crosswind, based on multi-rigid body dynamics and finite element method, the coupling model of the monorail vehicle-beam is established, in which the track beam is considered as a flexible sub-model; the vehicle includes traveling/steering/stabilizing wheels and evaluate the characteristics of tire sideways and slip. Crosswind was obtained by the Davenport spectrum and loaded on the vehicle. Dynamic responses of the vehicle-beam system and the safe running/wind speed were studied. The study shows that, for a car, the wind loaded outside balances part of the centrifugal action and eliminates part of the overturning trend of the vehicle when it turns but makes the lateral ride comfort deteriorate in the straight line section. For the beam, the wind loads help reduce the track beam's transverse deformation when cars pass, and the vertical deformation is slightly improved. For operation, when the running speed is less than 50 km/h and the wind speed is less than 15 m/s, the monorail vehicle can operate safely. The straddle monorail wind-vehicle-beam model can conveniently update the design parameters for dynamic calculation and comfort evaluation. It can provide a specific theoretical basis or guiding principles for the safe operation of straddle monorail vehicles under wind loads. [ABSTRACT FROM AUTHOR]

In the complex mountain wind environment, especially in the strong wind, fluctuating wind speed is a non-stationary and non-Gaussian random process. With the increase of suspension bridges' span, they are more sensitive to wind-induced vibration response. In this paper, a non-stationary and non-Gaussian buffeting reliability analysis method for long-span bridges is presented. Firstly, the non-stationary wind speed is simulated by the modulation function based on the stationary wind speed model. Secondly, the load is obtained by simulated wind speed, the obtained loads are loaded on the finite element model by ANSYS and the whole bridge time-domain analysis is performed, the time history of displacement response is obtained. Thirdly, based on the first excursion failure criterion of random vibration, the samples of the non-stationary and non-Gaussian displacement time history are transformed into a standard Gaussian process through a modified Fleishman approximation method, and then the non-stationary Poisson distribution method is used for structural reliability analysis. Finally, a mountainous long-span suspension bridge is used as the engineering background, and the proposed reliability analysis method is applied to analyze the reliability of the bridge. The influence of different wind attack angles and modulation functions on the dynamic reliability of the bridge is further studied. The results indicate that the displacement response obtained by the transformation of non-stationary and non-Gaussian random process is less reliable than that obtained by traditional analysis method. Its dynamic reliability is maximum at 1 ∘ wind attack angle, the reliability of negative wind attack angle is lower than that of positive wind attack angle, and decreases with the increase of wind attack angle. The reliability obtained by using different modulation functions is lower than that of traditional method. If the traditional analysis method is still used for reliability analysis, it will produce unsafe consequences and reduce the engineering safety reserve. [ABSTRACT FROM AUTHOR]

The purpose of this study is to investigate the flow field characteristics of the road-rail same-story asymmetric bridge deck and the influence of the asymmetric arrangement of the bridge deck on the flow field of the main girders. Numerical simulation tests were conducted on this bridge to analyze the distribution characteristics of the flow field near the main girder, as well as the aerodynamic characteristics of the railway bridge deck and highway bridge deck under different wind speeds and directions. The results indicate that the wind speed has less influence on the flow field distribution and aerodynamic characteristics of the road-rail same-story asymmetric bridge deck, but the incoming flow direction has a significant impact on its flow field characteristics. Compared to the railway bridge deck, during the reattachment position of the airflow, the highway bridge deck moves toward the windward side, and the volume of the separation bubble has been reduced, thus improving the effect on the negative pressure area of the railway bridge deck. The road-rail same-story asymmetric bridge deck has different aerodynamic interference characteristics for different wind speeds and different wind directions. [ABSTRACT FROM AUTHOR]

Reliable short-term wind speed prediction is one of the core technologies in the strong wind warning system for railway applications, which is of great significance for ensuring the safety of high-speed train operations and ancillary railway facilities. To improve forecasting accuracy, decomposition-based methods have attracted extensive attention due to their superior ability to address complex data characteristics (e.g., nonstationarity and nonlinearity). Currently, there are two pre-processing schemes for decomposition-based methods, i.e., one-time decomposition and real-time decomposition. In order to apply them better, this paper first expounds the difference between them, based on a combination of DWT (discrete wavelet transform) and CKDE (conditional kernel density estimation). The results show that although the one-time decomposition-based method has an unexceptionable accuracy, it only can provide offline prediction and thus may not be practical. The real-time decomposition-based method possesses stronger practicability and is able to provide online prediction, but it has limited accuracy. Then, an improved ensemble strategy is developed by optimizing the selection of appropriate decomposed components to conduct the prediction on the basis of real-time decomposition. This improved ensemble strategy provides an effective guidance for this selective combination, including taking historical information into consideration in the data. Finally, numerical examples and practicality analysis using two groups of measured wind speed data demonstrate that the proposed method is effective in providing high-precision online wind speed prediction. For example, compared with CKDE, the average degrees of improvement achieved by the proposed method in terms of MAE, RMSE, and MRPE, are 16.25%, 17.66%, and 16.93, respectively, while those compared with the traditional real-time decomposition method are 17.11%, 18.54%, and 16.84, respectively. [ABSTRACT FROM AUTHOR]

Signal complexity analysis based entropy measure has been used to propose a model-free approach towards assessment of flutter critical wind speed and identification of the type of flutter in wind tunnel testing of long span bridges. The approach is based only on the measured output responses from the structure, which accounts for appropriate effects that stem from the non-linearity of the structure and fluid structure interaction. The usefulness of the proposed approach has been demonstrated with dynamic sectional models of two deck cross-sections in wind tunnel. The gain in regularity of responses on approaching the flutter critical wind speed, demonstrated with time history of responses and recurrence quantification plots, has been quantified using sample entropy. Based on the sensitivity of the sample entropy values on the embedding dimension, it has been suggested to adopt embedding dimension in the range of 2 and 5, to obtain a swift estimate of the state of the dynamic system. The proposed approach has shown potential to provide valuable insight about the flutter instability and distinguish between different types of flutter without requiring prior knowledge about the system under consideration. The study offers a promising complementary methodology to the conventional model-based approaches for evaluating flutter critical wind speed. [ABSTRACT FROM AUTHOR]

To measure uncertainties of site-specific extreme loads for a signature bridge, a probabilistic method is developed based on structural health monitoring data in the Bayesian context. Compared with respective design loads, the probability of the predicted extreme load exceeding the design one is used to determine whether the design load is sufficient. The generalized Pareto distribution was first employed to model extreme value information. Then, Bayesian estimation was applied to predict probabilistic distributions of extreme loads, accounting for uncertainties within the prediction process. Finally, the effectiveness of the proposed method was validated through wind speed and temperature measurements from the Nanjing Dashengguan Yangtze River Bridge. The extreme wind speed and four types of thermal loads were predicted based on site-specific monitored loading data by using Bayesian estimation of the generalized Pareto distribution. As a result, the design wind speed and design change in uniform temperature are sufficient for the signature bridge. However, the probability that the predicted extreme vertical girder temperature difference exceeds the design one is 99.96%, and the probabilities subject to the transverse girder temperature difference and tower temperature difference are almost 100%. [ABSTRACT FROM AUTHOR]

Driving safety on horizontal curves under crosswinds has always been a concern for researchers. However, previous studies focused on single vehicles, especially single trucks. The safety of the truck platoon under crosswinds on horizontal curves was rarely examined. To fill such a gap, this study establishes a model for evaluating the safety of truck platoons under crosswinds on curves. After obtaining aerodynamic coefficients, a cosimulation model of a three-truck platoon is established with Trucksim and Simulink. The influencing factors on the lateral displacement of the truck platoon were analyzed, and the safety of the truck platoon under crosswinds on horizontal curves was then quantified with the response surface method. The results show that the fully autonomous platoon is safer than the human-led platoon. In a three-vehicle platoon, the smaller the lateral displacement of the truck, the further back the truck, and the lateral displacement of the vehicle increases with the loading of the truck. The safety index is computed to quantify the reliability of the truck platoon. The results indicate that the safety index increases with a decrease in the mean wind velocity and mean vehicle velocity and increases with an increase in the mean radius. When crosswinds come from the inside of the curve, the safety index increases with an increase in the mean superelevation; for crosswinds from the outside of the curve, the safety index rises with the drop of superelevation. The proposed approach can quantify the safety level of truck platoons under crosswinds on horizontal curves, and the results provide guidance to support the decision-making of transportation management agencies. [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]

Flexible suspension bridges are susceptible to aerodynamic instability phenomena. In this paper, the torsional divergence is addressed in terms of underlying mechanism, 3D and turbulence effects. A 3D generalized analytical model is first established by reasonable simplification of the model. Comparisons among results from different models are performed. The mechanisms of symmetric and asymmetric torsional divergence are explored. Finally, the 3D and turbulence effects are investigated. The results show that the proposed 3D generalized model is feasible for estimating the critical wind speed of asymmetric torsional divergence, and its computational accuracy is higher than the method provided by the code. The effects of turbulence on torsional divergence are multifaceted: the buffeting response due to wind fluctuations can significantly reduce the aerostatic stability of the bridge, resulting in a much lower critical wind speed than that in a smooth flow; the threshold of divergence is ambiguous and the instability is intermittent; further, the left and right quarter span sections largely vibrate in opposite directions during asymmetric torsional divergence. [ABSTRACT FROM AUTHOR]

Affected by many factors, the local wind environment on the bridge deck is complex and changeable, and it seriously threatens traffic safety. To accurately evaluate the wind field on the bridge deck, this paper develops a system to monitor the actual local wind environment and applies it to field measurement of the wind parameters at different positions of a complex truss girder bridge. The results show that the wind parameters on the bridge deck, including wind speed, gust factor, and turbulence intensity, are different from the bridge site due to the influence of the ancillary facilities. Also, the wind profile of the local wind field on the bridge deck is more in line with the polynomial distribution, which makes the equivalent height of the wind load much higher than the vehicle gravity. It should be noted that the measured power spectrum of the bridge deck is quite different from the wind spectrum applicable to the bridge site area, so it is not appropriate to use the wind spectrum of the bridge site area to carry out the analysis of the windmill bridge, and a more suitable wind spectrum for bridge deck wind field is proposed. [ABSTRACT FROM AUTHOR]

As no internationally agreed-upon method for determining safe speed values currently exists, collecting vast amounts of information on conventional ship behaviour could be used to train autonomous ship intelligence in determining safe speeds in different conditions. This requires speed data collected from conventional ships to resemble what can be described as safe speeds. To test this, the Automatic Identification System (AIS) and environmental data – namely visibility, mean wind speed and significant wave height – were collected and merged for two study areas in Norway in the period between 27 March 2014 and 1 January 2021. Regression analyses based on 47,490 unique vessel transits were conducted and supplemented by two graphical methods for revealing relationships between variables. Contrary to the contemporary understanding of safe speed, reduced visibility did not lead to significantly reduced transit speeds. Wind and waves caused a reduction in speed in the open ocean, but not in coastal waters. Transit speeds were lower in coastal waters than in the open ocean. [ABSTRACT FROM AUTHOR]

The flutter responses of the Nanjing No.4 bridge flat box girder under different wind attack angles were tested in detail through sectional model tests. The evolution of unsteady and steady critical amplitudes at different wind speeds was discussed. Based on the amplitude envelope of the flutter response and the Hilbert transform, the amplitude-dependent modal damping of the system was identified, and the mechanism of the flutter mode change with the wind angle of attack was initially explained. Secondly, the modal parameters of the system under different wind attack angles were extracted. With the bimodal coupled flutter analysis method, the nonlinear flutter derivatives of the section under different wind attack angles were identified, and the change law for the amplitude dependence of the key flutter derivatives on the wind attack angle and the potential influence on the section flutter morphology and characteristics, were studied. Finally, the effects of the wind attack angle on the uncoupled and coupled aerodynamic damping were analyzed through analyses of the modal damping subterms one by one, and the dynamic mechanism of the differential flutter performance caused by fractional damping was illustrated. [ABSTRACT FROM AUTHOR]

The Lanzhou-Xinjiang high-speed railway (HSR) traverses areas of the Gobi Desert where extremely strong winds are frequent. These strong winds cause sand/gravel hazards, an unaddressed issue that often seriously compromises the safe operation of the HSR. This paper studies the mechanisms leading to wind-blown sand hazards and the outcomes of sand control projects in these areas. The main findings are as follows: (1) Cold northern airflows over the Tian Shan mountain range are accelerated by the wind tunnels and downslope effect as they pass over complex terrain comprising passes, gullies, and proluvial fans. Consequently, the wind intensity often increases two- to threefold, creating frequent high-speed winds that lead to severe sand damage along the HSR. (2) In the Gobi areas with extremely strong winds, sand grains can be lifted as high as 9 m from the ground into the air, far higher than in other areas of the desert. The sand transport rate decreases exponentially with increasing height. Both wind speed and particle size determine saltation height. Coarser particles and stronger winds provide the particles with a higher kinetic energy as they collide with the ground. In the wind zones of Baili and Yandun, the analysed study areas, the saltation layer height of wind-blown sand/gravel exceeds 3 and 2 m, respectively. (3) Based on the above findings, recently emerging sand control materials, suitable for the areas of interest, were screened and developed. Furthermore, under the proposed principle of 'supplementing blocking with trapping', a comprehensive sand control measure was established, featuring sand-blocking belts comprised of multiple rows, and high, vertical sand-trapping installations with a large grids size. The installed system showed a high efficacy, reducing sand transport rate by 87.87% and significantly decreasing the deposition of sand along a trial section of the HSR. [ABSTRACT FROM AUTHOR]

Short-term forecasting of wind gusts, particularly those of higher intensity, is of great societal importance but is challenging due to the presence of multiple gust generation mechanisms. Wind gust observations from eight high-passenger-volume airports across the continental United States (CONUS) are summarized and used to develop predictive models of wind gust occurrence and magnitude. These short-term (same hour) forecast models are built using multiple logistic and linear regression, as well as artificial neural networks (ANNs) of varying complexity. A suite of 19 upper-air predictors drawn from the ERA5 reanalysis and an autoregressive (AR) term are used. Stepwise procedures instruct predictor selection, and resampling is used to quantify model stability. All models are developed separately for the warm (April--September) and cold (October--March) seasons. Results show that ANNs of 3--5 hidden layers (HLs) generally exhibit higher hit rates than logistic regression models and also improve skill with respect to wind gust magnitudes. However, deeper networks with more HLs increase false alarm rates in occurrence models and mean absolute error in magnitude models due to model overfitting. For model skill, inclusion of the AR term is critical while the majority of the remaining skill derives from wind speeds and lapse rates. A predictive ceiling is also clearly demonstrated, particularly for the strong and damaging gust magnitudes, which appears to be partially due to ERA5 predictor characteristics and the presence of mixed wind climates. [ABSTRACT FROM AUTHOR]

Based on the aerostatic force model under skew wind, considering the nonlinear and three-dimensional effects of aerostatic forces and also structural geometric nonlinearity, a method of three-dimensional nonlinear aerostatic stability analysis under skew wind is presented, and the corresponding computational procedure (SNAA-SW) is developed. By taking a suspension bridge- the Runyang suspension bridge over the Yangtze River as example, 3D nonlinear aerostatic stability analysis of the bridge under skew wind is conducted, and the skew wind effect on the aerostatic stability of long-span suspension bridges is ascertained. The results show that the skew wind effect does not change the aerostatic instability mode of suspension bridges, which shows a spatial bending-torsion coupled instability mode as the same as normal wind case. The skew wind has positive and negative effects on the aerostatic stability of suspension bridge under different wind attack angles, and the evolutions of critical wind speed of aerostatic instability with wind yaw angle are completely different from the cosine rule as proposed by the skew wind decomposition method, for most cases, the lowest critical wind speed of aerostatic instability occurs under skew wind. With the increase of wind yaw angle, the skew wind effect on the critical wind speed of aerostatic instability becomes more prominent, and the influence is between −10.7% and 8.1%. Therefore, the skew wind effect needs to be accurately considered in the aerostatic stability analysis of long-span suspension bridges in particular at large wind yaw angles. [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]

Flutter may lead to collapse of long-span bridges and need to be avoided, which makes the estimation of the onset flutter essential for long-span bridge design. However, the efficiency of traditional solution methods of predicting onset flutter is not high. In this study, it is converted into an optimization model, which is solved by a proposed advanced particle swarm optimization (APSO) with a novel inertia weight strategy and mutation mechanism. Two well-known benchmark functions are firstly employed to validate the performance of APSO. Compared with other existing PSO methods, APSO not only has high accuracy, but also has the fastest convergence speed. Then, APSO is used to find the flutter critical wind speed of bridges. A good agreement is obtained comparing predictions on the onset flutter by the proposed methods and available tests on several study cases. In addition, the value range of APSO variables is discussed in depth. It is confirmed that the proposed APSO algorithm has excellent stability, robustness and fast convergence, which is suitable for searching onset flutter of bridges. [ABSTRACT FROM AUTHOR]

Nonlinear flutter behaviors of a π-shaped sectional bridge deck are investigated numerically, focusing on the effects on the post-flutter limit cycle oscillation (LCO) amplitudes caused by various nonlinearities, including aeroelastic, structural damping, and geometric nonlinearity. The Multi-stage indicial functions (IFs) are adapted to describe the nonlinear aeroelastic effects in time-domain, which necessitate amplitude-dependent aeroelastic model parameters. The motion amplitude-dependent parameters are mainly extracted numerically with computational fluid dynamics (CFD) method and partially examined by experimentally extracted results. The CFD-based parameters turn out to be satisfactory compared with experimental results. Finally, the flutter thresholds and post-flutter limit cycle oscillations are simulated using the present time-domain multi-stage indicial functions model. The numerical results show that introduction of any one kind of nonlinearity (aeroelastic, structural damping, or geometric) in the numerical procedure can lead to LCO. These three kinds of nonlinearity are compared in detail in terms of the effects they have on the post-flutter LCO amplitude. It turns out that the damping nonlinearity, for the case concerned in this work, is the most important factor that determines the post-flutter LCO amplitude and the flutter onset wind speed as well. The time-domain multi-stage indicial functions procedure adopted in this work can serve as an efficient solving strategy to obtain nonlinear post-flutter performances of long-span bridges. [ABSTRACT FROM AUTHOR]

Although the wind barrier was set near the bridge tower, more than 10 traffic accidents under crosswinds happen in the bridge tower area within 1 month of the opening operation of a cross-sea bridge. To investigate the wind shielding effect of the bridge tower, a field measurement scheme of wind-vehicle-bridge system, which is a step-by-step test method, was presented and performed on a long span cable-stayed bridge. Firstly, the horizontal profile of wind speed of bridge deck near bridge tower was obtained through the anemometers. Then, the dynamic response of the bridge was measured under the action of normal operating vehicle when the natural wind speed is low. Finally, the response of the moving car was measured when passing through bridge tower, and the wind speed was recorded simultaneously. The results show that the wind-vehicle-bridge system can be tested by step-by-step test method to understand the wind shielding effect of bridge tower. The displacement response of the bridge is still very small when two large trucks meet, and the coupling effect between the vehicle and the bridge is insignificant when a single car passes through the bridge tower. Due to a large porosity of the anti-collision guardrail, the wind speed at the height of 1 m from the bridge deck has changed dramatically when the car leaves the bridge tower on the windward and entering or leaving the bridge tower on the leeward. Among them, the leeward side change is more obvious, and the response of the leeward side vehicle is also greater. The suitable decrease of the anti-collision guardrail porosity in the bridge tower region will improve the running safety of vehicles. [ABSTRACT FROM AUTHOR]

In order to analyze the change characteristics and influencing factors of the total suspended particulate ( TSP)concentration in the atmosphere of coal port area, using the monitoring data of the typical coal port area in 2020, based on the K-means clustering method, the change characteristics of the TSP concentration in the port area were analyzed; combining with the characteristic parameters of meteorological environment in the port area, the correlation between TSP pollutant concentration changes and humidity and wind speed were analyzed. The results show that the overall TSP mass concentration in the port area has a positive and negative correlation with humidity and wind speed, respectively. The concentration daily change trend is "single peak and single valley" type, the peak and valley values arrive at 5： 00 -7： 00 and 17： 00 -18： 00respectively. Abnormal fluctuations are prone to occur in summer and winter. And it shows 6 different clustering characteristics of hourly variation patterns. The research results can provide theoretical support for the prevention and control of particulate pollution in coal port areas [ABSTRACT FROM AUTHOR]

In recent years, extreme atmospheric events are becoming increasingly frequent and unpredictable. These phenomena are often characterized by low-frequency variations of the wind speed and angle of attack, mainly due to large-scale turbulence. These features can be critical for long-span bridges as they can lead the deck in conditions where the nonlinear effects of aerodynamic forces are enhanced. Therefore, it is increasingly important to develop reliable numerical tools to simulate the response of these structures to non-synoptic winds. In this work, a nonlinear rheological model that is able to account for the large variations in wind speed and angle of attack is employed to investigate the dynamic response of two different bridges subjected to two different wind fields. The first scenario is a standard synoptic wind field used as a baseline. On the other hand, the second wind scenario represents an extreme non-synoptic atmospheric event. The results highlight how the nonlinear effects of the aerodynamic forces, in particular those related to the large variation of the angle of attack, could lead to significant changes in the bridges' response. These effects would not be captured by employing standard linearized methods. • Non-synoptic atmospheric events exhibit low-freq variations in wind speed and angle of attack. • Related nonlinear aerodynamic effects strongly influence the response of long-span bridges. • A nonlinear rheological model able to include these effects is presented. • The model helps to assess the behavior of bridges under extreme atmospheric events. [ABSTRACT FROM AUTHOR]

Bridges and subgrades are the main route forms for expressways. The ideal form for passing through sandy areas remains unclear. This study aims to understand the differences in the influence of expressway bridges and subgrades on the near-surface blown sand environment and movement laws, such as the difference in wind speed and profile around the bridge and subgrade, the difference in wind flow-field characteristics, and the difference in sand transport rate, to provide a scientific basis for the selection of expressway route forms in sandy areas. Therefore, a wind tunnel test was carried out by making models of a highway bridge and subgrade and comparing the environmental effects of wind sand on them. The disturbance in the bridge to near-surface blown sand activities was less than that of the subgrade. The variation ranges of the wind speed of the bridge and its upwind and downwind directions were lower than those of the subgrade. However, the required distance to recover the wind speed downwind of the bridge was greater than that of the subgrade, resulting in the sand transport rate of the bridge being lower than that of the subgrade. The variation in the wind field of the subgrade was more drastic than that of the bridge, but the required distance to recover the wind field downwind of the bridge was greater than that of the subgrade. In the wind speed-weakening area upwind, the wind speed-weakening range and intensity of the bridge were smaller than those of the subgrade. In the wind speed-increasing area on the top of the model, the wind speed-increasing range and intensity of the bridge were smaller than those of the subgrade. In the wind-speed-weakening area downwind, the wind speed weakening range of the bridge was greater than that of the subgrade, and the wind speed-weakening intensity was smaller than that of the subgrade. This investigation has theoretical and practical significance for the selection of expressway route forms in sandy areas. [ABSTRACT FROM AUTHOR]

To evaluate the crosswind stability (overturning and sideslip) of vehicles driving on the bridge, obtaining critical wind speed is essential. The traditional method is based on the aerodynamic forces of moving vehicles on the bridge and the analysis of force equilibrations. However, various shapes of the bridge make the flow field around the vehicle on the bridge very complicated to obtain. In this paper, a simplified method is introduced to calculate the critical wind speeds of moving vehicles on bridges based on the influence of coefficients of the wind environment on the bridge and the aerodynamic forces of moving vehicles on open fields. The aerodynamic forces of moving vehicles are simulated with dynamic mesh techniques. Besides, the characteristics of the wind environment on the bridge deck are studied to evaluate the driving safety and determine the influence coefficient. To further demonstrate the reliability, critical wind speed in different road conditions of the proposed simplified method shows very good agreement with the traditional method. [ABSTRACT FROM AUTHOR]

For rail vehicles, the spanwise correlation of aerodynamic forces acting on a single car is usually overlooked. To investigate the effects of spanwise correlation functions on the dynamic responses of the rail vehicle-bridge coupling system, firstly, the forms of spanwise correlation functions in the aerodynamic forces of a running vehicle, which are associated with the longitudinal and vertical fluctuating wind speeds, were proposed. Secondly, the spectra of buffeting forces acting on the running vehicle considering those spanwise correlation functions were obtained. Thirdly, a rail vehicle-bridge coupling system was established by using the commercial software SIMPACK, and a single car running on a typical high-speed railway bridge was taken as an example. Again, the effects of artificial discrete wind fields on the dynamic responses of the vehicle and bridge were investigated. Finally, the effects of the above spanwise correlation functions on the dynamic responses of the rail vehicle-bridge coupling system were compared under the cases of different vehicle speeds and wind speeds. The results show that different discrete time intervals can exert significant effects on the vehicle responses, and the discrete time interval of 0.05 s can be used for analysis in the wind-rail vehicle-bridge coupling system. With the increase of vehicle speed, the values of vehicle and bridge responses considering the spanwise correlation functions tend to be close to those without considering the spanwise correlation functions. However, as the wind speed increases, the values of vehicle and bridge responses generally tend to show greater differences in the presence and absence of spanwise correlation functions. At different vehicle speeds or wind speeds, the spanwise correlation functions have significant effects on the RMSs of vehicle accelerations and bridge lateral acceleration, but they have little effects on the bridge vertical acceleration. [ABSTRACT FROM AUTHOR]

High-sided vehicles are particularly vulnerable to high wind conditions and at sites that are regarded as vulnerable, a range of vehicle restrictions are imposed in high winds. These may include vehicle speed reductions or complete restrictions on the movement of different categories of vehicle at different wind gust speeds. This paper builds on earlier work that has been carried out and seeks to develop a simple but conservative method that can be used to specify vehicle restriction strategies. This is based on a collation of a wide range of data for aerodynamic rolling moment coefficients that allows a simple parameterisation to be developed. This is then used in an overturning model to develop a non-dimensional relationship between overturning gust speed and vehicle speed. The parameter used in the non-dimensionalisation is a characteristic wind speed that is a function of vehicle weight and geometry, and effectively specifies the vulnerability of the vehicle to overturning in high winds. Dimensional relationships between overturning gust velocities and vehicle velocities can thus be derived for different vehicle types and used to develop site-specific vehicle restriction methods. [ABSTRACT FROM AUTHOR]

This study provides a theoretical explanation for a perplexing experimental phenomenon observed frequently in suspension bridge flutter testing, where the flutter critical wind speed (U cr) predicted by two-dimensional (2D) section model testing is higher than that predicted by three-dimensional (3D) full aeroelastic model testing. Six long-span suspension bridges with either a single simply supported span or multiple continuously supported spans were taken as research examples, then the comparative studies on the flutter critical wind speeds, flutter frequencies, modal energy ratios and aerodynamic damping corresponding to 2D and 3D coupled flutter states were carried out to illustrate the flutter modal effects. The research findings indicate that the U cr of 2D testing being higher than that of 3D testing is an inherent characteristic for single-span simply-supported suspension bridges, which can be attributed to the prominent aerodynamic negative damping associated with 2nd-order vertical bending mode. However, due to the aerodynamic positive damping associated with 3rd-order vertical bending mode, the U cr of 2D testing is consistently lower than that of 3D testing in the cases of multi-spans continuously-supported suspension bridges. Additionally, to eliminate unsafe 2D evaluations, a reasonable modal matching principle is recommended for section model testing of single-span simply-supported suspension bridges. • The modal effects of span-layout types on coupled flutter of suspension bridges are clarified. • The reasons for the unsafe 2D flutter evaluations compared to 3D evaluations are revealed. • An improved modal matching suggestion is proposed to eliminate unsafe 2D evaluations. [ABSTRACT FROM AUTHOR]

The purpose of this study is to explore the application of numerical simulation methods in determining the design wind speed for large-span bridges situated in mountainous terrain. Compared to isolated mountains, the simulation of continuous mountain is more complex and often requires a larger computational domain. This implies that excessively high terrain model resolution can compromise computational resources. However, existing studies lack insights into selecting the optimal size of terrain extent, terrain model resolution, as well as the form of truncation curve. In this study, the impacts of terrain model resolution and size of terrain extent are discussed. In addition, the results from various transitional sections are compared against field measurement data. The results show that the UBTS transitional section form with the terrain resolution of 300 m and a diameter of 30 km of the mountain terrain can yield a reasonable simulation result at the bridge site. Furthermore, the research adopts the Xingkang bridge as a case study to outline the steps of determine the design wind speed for mountain bridges. The findings of this research offer valuable guidance for an appropriate numerical method in the practical engineering applications in determining the design wind speed for bridges in mountainous areas. • The terrain model with a horizontal geometry resolution of 300 m is adequate to get a reasonable result. • The adoption of the terrain model with a diameter of 30 km could yield a reasonable result. • The transitional form of UBTS models shows the best performance compared with the field measurements data. • The process of the determining the design wind speed of mountain bridge is illustrated. [ABSTRACT FROM AUTHOR]

• A method for estimating full set of amplitude-dependent FDs at the whole wind speed regime from free vibration wind tunnel tests is proposed and validated. • The evolution characteristics of the nonlinear coupled and uncoupled aerodynamic damping with wind speed and vibration amplitude were revealed. • The influence of structural parameters on the post-flutter performance were investigated based on the developed 2D nonlinear flutter analysis method. • The influences of vertical DOF (mode) and 3D effects on nonlinear flutter response were revealed based on the developed 3D nonlinear flutter analysis method. To estimate nonlinear flutter response of long-span bridges, this study established a method for identifying full set of amplitude-dependent flutter derivatives (FDs) from free vibration wind tunnel tests. Taking a typical double-deck truss bridge as a Case study, the amplitude-dependent FDs of the bridge deck at the whole wind speed regime are identified and cross-validated based on large-amplitude free vibration wind tunnel tests of its single degree of freedom (SDOF) torsional and 2DOF vertical-torsional section models. The influential mechanism of vertical DOF on nonlinear flutter was revealed by quantitatively comparing the nonlinear aerodynamic damping of the SDOF and 2DOF systems. The amplitude-dependent FDs are then used to calculate the nonlinear flutter responses of the 2D bridge section and a prototype long-span suspension bridge (1650m) with four main cables based on developed 2D and 3D nonlinear flutter analysis methods. Finally, the influence of structural parameters and 3D effects on nonlinear flutter are quantified and discussed. The results show that the 2DOF system has a lower critical wind speed and higher torsional stable amplitudes compared with the SDOF system since the participation of vertical DOF introduces the negative coupled aerodynamic damping to the system. The aerodynamic nonlinearity becomes stronger and stronger as the wind speed increases and it mainly leads to the significant amplitude dependence of the uncoupled aerodynamic damping, which is the key factor to cause the limit cycle oscillation (LCO)-type of flutter. While the coupled aerodynamic damping appears to be a relatively linear damping with weak amplitude-dependence within the studied wind speed and it mainly plays the role of reducing the stability of the system. The 3D effects of the vibrating bridge deck will reduce the system stability mainly by increasing the negative uncoupled aerodynamic damping. Therefore, the amplitudes of nonlinear flutter will be seriously underestimated if the 3D effects are ignored. [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]

• The upper and lower surfaces of the deck are the vibration-induced parts. • The phase raise of lift leads to unsteady galloping instability. • Barriers' porosity or height change aerostability while their processes differ. • Mechanical damping is not a decisive parameter affecting critical wind speed. The long-span bridges with truss beam are widely recognized as typical wind-sensitive structures, and its wind-induced divergence events may become a very predominant issue. This work evaluates the galloping performance of a typical truss beam with wind barriers, which is detected to be susceptible to the infrequent vertical instability at specific attack angles, as evidenced by experimentation and numerical analysis. Since the truss beam constitutes a complex cross section, this study employs energy analysis to distinguish the crucial parts affected by vibration and discovers that the galloping vibration is mostly caused by the surfaces of the deck. Rather than relying on conventional quasi-steady theory, this study explores the unsteady aerodynamic forces to identify the underlying galloping driving mechanism. Our findings reveal that the instigator of galloping instability is the phase rising of lift with increasing wind speed. Additionally, the nonlinear mechanical damping is not a decisive parameter. Furthermore, we have investigated the impact of an essential ancillary facility, the wind barrier, and discovered that its galloping stability can be enhanced by increasing its porousness and decreasing its height. However, the underlying mechanisms behind this improvement are distinct. [ABSTRACT FROM AUTHOR]

• Using surrogate models for uncertainty propagation in bridge buffeting is efficient. • Sensitivity analysis is used to determine critical parameters on buffeting response. • Surrogate models are validated via comparison with direct Monte Carlo simulations. • Wind-induced fragility of a long-span bridge is analyzed under three wind climates. Buffeting of long-span bridges caused by the wind turbulence could result in problems of large deformation, fatigue, traffic safety and user comfort. The calculation of buffeting responses is greatly affected by multiple uncertainties, especially the randomness of flutter derivatives and structural damping. In buffeting analysis, these uncertainties are typically propagated using the brute-force Monte Carlo (MC) method, which requires enormous computational resources for a complicated structure involving multiple uncertainties. This study develops an efficient framework based on surrogate models to account for these uncertainties in buffeting responses and the assessment of structural fragility in a mixed climate. Two surrogate models, Kriging and polynomial chaos expansions (PCE), are applied in this framework. Comparison with the direct MC method shows that the Kriging model rather than the PCE model is the proper surrogate model, and the surrogate model contributes significantly to saving computing time from 17 h to 1 min for MC simulations. It is also observed that uncertainties propagated from structural parameters to responses will be more notable as the wind speed increase. Buffeting fragility curves of this bridge show that it's easier for responses in acceleration to achieve and exceed thresholds, indicating that performance related to user comfort might not be satisfied. By introducing the probability distributions of non-typhoon and typhoon winds at the site of the bridge, it is found that considering single climate may underestimate structural risk. The framework based on surrogate models in this paper can be further generalized to additional PBWE frameworks addressing different wind and structural engineering issues. [ABSTRACT FROM AUTHOR]

In this study, the influences of wind barriers on the aerodynamic characteristics of trains (e.g. a CRH2 train) on a highway-railway one-story bridge were investigated by using wind pressure measurement tests, and a reduction factor of overturning moment coefficients was analyzed for trains under wind barriers. Subsequently, based on a joint simulation employing SIMPACK and ANSYS, a wind–train–track–bridge system coupled vibration model was established, and the safety and comfort indexes of trains on the bridge were studied under different wind barrier parameters. The results show that the mean wind pressures and fluctuating wind pressures on the trains' surface decrease generally if wind barriers are used. As a result, the dynamic responses of the trains also decrease in the whole process of crossing the bridge. Of particular note, the rate of the wheel load reductions and lateral wheel-axle forces can change from unsafe states to relative safe states due to the wind barriers. The influence of the porosity of the wind barriers on the mean wind pressures and fluctuating wind pressures on the windward sides and near the top corner surfaces of the trains are significantly greater than the influence from the height of the wind barriers. Within a certain range, decreasing the wind barrier porosities and increasing the wind barrier heights will significantly reduce the safety and comfort index values of trains on the bridge. It is found that when the porosity of the wind barrier is 40%, the optimal height of the wind barrier is determined as approximately 3.5 m. At this height, the trains on the bridges are safer and run more smoothly and comfortably. Besides, through the dynamic response analysis of the wind–train–track–bridge system, it is found that the installation of wind barriers in cases with high wind speeds (30 m/s) may have an adverse effect on the vertical vibration of the train–track–bridge system. [ABSTRACT FROM AUTHOR]

Based on the aerostatic and self-excited aerodynamic force models, a computational approach of three-dimensional (3D) refined flutter analysis for long-span bridges under skew winds is established, in which the structural nonlinearity, aerostatic effect and full-mode coupling effect, etc., are fully considered, and the computational procedure (N flutter-sw) is developed accordingly. By taking the Runyang Suspension Bridge over the Yangtze river as an example, under the wind attack with initial angles of 0∘ and ± 3 ∘ and yaw angles between 0∘ and 25∘, the flutter stability of the bridge in completion under skew winds is analyzed, and the influences of skew wind and aerostatic effect on the flutter stability of suspension bridges are assessed. The results show that the aerostatic effect has a significant influence on the flutter stability of long-span suspension bridge, and it may worsen its flutter stability, with an average decrease of 6.0%. However, it does not change the evolution of flutter stability of suspension bridge with increasing wind yaw angle. The critical flutter wind speed fluctuates with the increase of wind yaw angle, and it reaches the lowest value mostly under the skew wind, with an average reduction of 8.0%. The combined influence of the aerostatic effect and skew wind further reduces the flutter critical wind speed by 11.5% on average, and therefore, the aerostatic effect, skew wind effect and their adverse influences need to be comprehensively considered in the flutter analysis of long-span suspension bridges. [ABSTRACT FROM AUTHOR]

The downwash airflow field is an important factor influencing the spraying performance of plant protection UAV, and the structural design of rotors directly affects the characteristics of the downwash airflow field. Therefore, in this study, three-dimensional models of a six-rotor UAV with various inner tilt angles were established to simulate and analyze the influence of the inner tilt angle on the downwash airflow field based on the Reynolds average NS equation, RNG k-e turbulence model, etc.. On this basis, a wireless wind speed acquisition system using the TCP server was developed to carry out the test through the marked points with real-time detection. The simulation results show that, the variation of inner tilt angles of the six-rotor UAV did not cause significant difference in the time dimension of the downwash airflow field, and with the change of the inner tilt angle from 0° to 8°, the distribution of downwash airflow field tended to obliquely shrink towards the central axis direction, and the amplitude of linear attenuation of airflow speed was also increased, which the difference of attenuation amplitude was 1 m/s. Besides, under the different inner tilt angles, the airflow velocity in "lead in area" was significantly greater than that in the "lead out area", and the difference of air velocity distribution in space would affect the uniformity of droplet deposition. Through the calibration test, the measurement accuracy error of the developed system was lower than 0.3 m/s, and the adjusted R2 of the calibration fitting equation was higher than 0.99. The test and simulation values at test points from 0.2-2.3 m below the rotors exhibit the same variation trend, and the average relative error at the height of 1.1-2.3 m below the rotors and 0.2-0.8 m near the ground was within 10% and 20%, respectively. The simulation and test results were highly reliable, which could provide basis and reference for the design and optimization of plant protection drones. [ABSTRACT FROM AUTHOR]

Steel truss stiffening girders are widely used when designing long-span bridges in mountainous areas owing to their distinct characteristics compared to the streamlined box girder. However, natural wind in mountainous areas is very complex with high turbulence and large attack angles which adversely affect the flutter performance of long-span bridges with truss girders. Aerodynamic countermeasures are widely adopted to improve flutter performance. This paper studies the flutter performance and the effects of various aerodynamic countermeasures on the flutter improvement of a 1060 m truss-stiffened girder suspension bridge spanning mountainous canyon by wind tunnel tests of the sectional model and full-bridge model. First, sectional model tests with the original girder section were carried out under various wind attack angles. Subsequently, to improve the flutter stability of the bridge under the most unfavorable wind attack angle, several aerodynamic countermeasures including central upper stabilizer, horizontal stabilizer, combined central upper and horizontal stabilizers, and sealed central traffic barrier were proposed and sectional model tests with optimized girders were conducted. The results show that the aerodynamic mitigation effect of the central upper stabilizer, horizontal stabilizer, as well as combined measure, is closely related to the geometric dimension of the stabilizing plate. It is found that large geometric dimensions effectively increase the flutter critical wind speed of the truss girder. Considering sealed central traffic barrier measure, the smaller ventilation rates result in larger flutter critical wind speed of the girder. The sealed central traffic barrier measure with a 50 % ventilation rate is deemed as the most optimal aerodynamic countermeasure in consideration of aesthetics, economy, and safety. Finally, the effectiveness of optimal countermeasure is validated through an aeroelastic full-bridge model test. The research is conducted to provide references on flutter performance optimization of similar bridges in the future. [ABSTRACT FROM AUTHOR]

To investigate the effects of thunderstorm downburst on the characteristics of wind field at bridge sites in flat and gorge terrains, firstly, numerical simulation of wind fields in the flat terrain under the thunderstorm downburst was conducted through the SST k-ω turbulence model, combined with the impinging jet technology. After verification of the reliability of the numerical model, settings, and methods, the characteristics of wind field over a long-span bridge site in a gorge terrain under the thunderstorm downburst were investigated and the distributions of wind speed and wind attack angle in the flat and gorge terrains were compared. The results show that, under the effects of the thunderstorm downburst, the wind speeds are relatively maximum at the midspan point of the girder in the flat terrain. Besides, the farther away from the midspan point, the smaller the wind speeds, which is opposite to the case in the gorge terrain. The wind speeds at each typical monitoring point are basically the same in the two terrains, before the thunderstorm downburst hits the bridge girder. Later the wind speeds at each point in the gorge terrain are much higher than those in the flat terrain. Most wind attack angles are negative at the monitoring points in the flat terrain, but the farther away they are from the midspan point, the greater the wind attack angles will be. However, the wind attack angles at the monitoring points in the gorge terrain are generally larger than those in the flat terrain, and they gradually turn to be positive farther away from the midspan point. In the flat terrain, both wind speeds and wind attack angles (or their absolute values) at the girder are large within about t = 75∼130 s, indicating that the thunderstorm downburst may exert significant effects on the bridge. However, in the gorge terrain, due to the large wind speeds and wind attack angles (or their absolute values) at the girder after t = 75 s, full attention needs to be paid to the effects of the thunderstorm downburst during this period. [ABSTRACT FROM AUTHOR]

Summary: From 2010 to 2016, wind speed time history and synchronous acceleration responses along Xihoumen Bridge (XB) girder were recorded by a health‐monitoring system. Based on this dataset, wind speed, wind direction, angle of attack (AoA), turbulence intensity, and turbulence length scale are studied based on 10‐min time intervals. The environmental wind characteristics and synchronous structural effects are decoupled by the control variable method. The probabilistic dependence between wind parameters and structural responses is explored by explicit polynomial regression equations. With wind environment parameters as input, the acceleration responses of the bridge could be rapidly predicted with a certain confidence interval using decoupling and regression modeling (DRM). The proposed DRM can reproduce the buffeting acceleration responses when the bridge is subject to future potential strong typhoon attacks. The key factors affecting the buffeting responses of XB are analyzed and discussed. Generally, the buffeting acceleration responses of XB are significantly affected by wind speed and turbulence intensity rather than by turbulence length scale, which agrees well with previous observations. [ABSTRACT FROM AUTHOR]

Flutter control is necessary in the design of a long-span bridge. With the help of active flaps, flutter control can suppress flutter vibration and increase aerodynamic stability. This study aims to build a theoretical framework for active flutter control using a system consisting of a streamlined box girder with adjacently mounted active flaps (noted as a "deck-flap system"). An adaptive expression was proposed for the system's self-excited forces, and an identification method was established for obtaining the system flutter derivatives in consideration of the bluff characteristics of the bridge deck and the aerodynamic interactions between the bridge girder and flaps. Then, the suboptimal control algorithm was implemented into the deck-flap system to simultaneously stabilize the divergent oscillation at the designed wind speed. Based on the proposed approach, numerical simulations were conducted to investigate the system flutter derivatives and the effectiveness of the control law. A comparison between the critical speeds of the two-dimensional flutter analysis and a fluid-structure interaction simulation showed a satisfactory performance from the theoretical model and the reliability of the identification method. The vibrations of the deck-flap system were successfully suppressed by the controlled motions of the active flaps under the application of the suboptimal control algorithm. This study provides a reliable framework for conducting an analysis of active control for bridge flutter and for significantly increasing the flutter stability of a deck-flap system. [ABSTRACT FROM AUTHOR]

An assessment of 3D-printed span-change structures is presented for determining suitability of the technology to small unmanned aerial vehicles. Materials and manufacturing technologies were used with an emphasis on near term applicability with design trades between the aerodynamic performance and structural response. Aerodynamic performance was assessed on three wind tunnel models varying span (432, 600, and 762 mm), wind speed (Reynolds numbers 18,000, 36,000, and 71,000), additive manufacturing print build plane and camber, quantifying structural response as the resulting shape during aerodynamic loading. Each model displayed increasing compliance as span increased with wing-tip displacement on the order of 50, 100, and 200 mm with various degrees of sweep and twist. Models generated excess lift at Re = 71,000 indicating potential flight demonstration of the technology with a lift to drag improvement of up to 97% at maximum wing extension. [ABSTRACT FROM AUTHOR]

The simulation of fluctuating wind speed fields holds paramount importance in the wind-resistant design of significant structures such as high-rise buildings, long-span bridges, and wind turbines. To address the computational challenges posed by the original spectral representation method (SRM), a novel approach has emerged. This approach, rooted in the frequency-wavenumber spectrum (FWS), offers a solution to the complexities associated with the original SRM. An enhanced non-uniform discrete technique based on the acceptance-rejection (A-R) criterion was introduced to improve the efficiency of the FWS-based SRM. Nonetheless, this technique currently faces certain constrains, including its demand for a substantial allocation of random access memory (RAM) and its inability to be seamlessly integrated with the fast Fourier transform (FFT) algorithm. Given this scenario, a notably more effective strategy for selecting representative points emerges -the frequency-dependent acceptance-rejection (A-R) scheme. This innovative scheme holds the advantage of diminishing RAM utilization, transforming wind field modeling from a supercomputers-exclusive task to one feasible on personal computers. Moreover, its seamless integration with FFT technology bolsters simulation efficiency. The provided numerical simulation instances of two-spatial dimensional fluctuating wind speed fields underscore the proficiency of this proposed frequency-dependent A-R scheme. The outcomes demonstrated the combined A-R and FFT technique's efficiency and precision, in simulating two-spatial dimensions fluctuating wind speed fields. [ABSTRACT FROM AUTHOR]

Multi-mode vertical vortex-induced vibrations have been observed on several long-span suspension bridges, where several vertical modes of stiffening girder are excited in turn with increasing of wind velocity. This paper proposed a discrete viscous dampers solution and its optimization targeting multi-mode vortex-induced vibration control for long-span suspension bridges. The minimal modal damping ratio was used to evaluate the performance of the damper system. The wind tunnel test verified that the modal damping ratio is an alternative to the resonance response amplitude and can be obtained by complex modal analysis. The ternary search algorithm was adopted to find the optimal damper parameter for the Yingwuzhou Yangtze River Bridge, which is a suspension bridge that suffered excessive vortex-induced vibrations. Using linear damper elements to connect the bridge tower and the bridge girder directly turned out to be a feasible method of increasing multiple modal damping ratios. Four torsional eddy current dampers have been installed in the Yingwuzhou Yangtze River Bridge, based on the numerical optimization results calculated in this paper. Although the measured modal damping ratios were smaller than the numerical results, the structural damping increased by three times after dampers were installed, and the requirement of the current specification was satisfied. • A discrete viscous dampers solution is proposed for multi-mode vortex-induced vibration control. • The conception of choosing the optimal damper parameter is discussed. • The modal damping ratio is an alternative to the resonance response amplitude. • Ternary search algorithm was adopted in finding the optimal damper parameter. • Solution was applied and verified in the Yingwuzhou Bridge. [ABSTRACT FROM AUTHOR]

• Full-bridge tests reveal flutter modality has significant high-order heaving modes. • Modality-driven method utilizing genetic algorithms is developed to clarify the modal effects. • Second-order mode dominates flutter modality but has smaller contribution than first-order mode. Modal coupled effects concealed in the semblance of flutter dominated by torsional modes have an uncertain impact on the flutter characteristics of long-span bridges, making it challenging to fully comprehend the underlying physics of three-dimensional flutter. Consequently, this research has investigated the composition of flutter modality and its related modal effect mechanism through experimental and theoretical analyses. Initially, the actual flutter modality and its compositions were ascertained through full-bridge aeroelastic tests on four suspension bridges with main spans exceeding 1750 m. Subsequently, the practical modality-driven flutter analysis was developed to measure the impact of each natural mode, particularly the higher-order mode, on the flutter performance through modal-generated aerodynamic damping. Next, the genetic algorithm was introduced in this method to enhance the convergence robustness. Finally, a systematic investigation was conducted to examine the evolution of modal effects with changes in the main spans. The results of full-bridge aeroelastic tests indicate that the flutter pattern is predominantly formed by the first-order symmetric torsional mode, the first-order symmetric heaving mode, and the second-order symmetric heaving mode. In terms of modal participation and modal aerodynamic damping contribution, the second-order mode governs the flutter heaving modality but has a smaller impact on the flutter performance compared to the first-order mode. The first-order torsional mode and the first-order heaving mode provide continuously increasing positive damping and continuously decreasing negative damping respectively, while the aerodynamic damping provided by the second-order heaving mode exhibits a turning phenomenon as wind velocities increase due to the system frequency approaching the second-order natural frequency. The genetic algorithm can effectively address potential occurrences of non-convergence or switching phenomena in numerical calculations. [ABSTRACT FROM AUTHOR]

To assess the reliability of wind resistance behavior for long-span cable-stayed bridges, this study establishes a joint probability distribution model for 10-minute mean wind speed and turbulence intensity based on one year of field monitoring data. Firstly, the distribution characteristics of wind parameters at the deck height are investigated. Notably, substantial abnormalities are observed in the anemometer data obtained from the upstream and downstream sides of the mid-span deck. Thus, a novel component-decomposition method is proposed to eliminate these inconsistencies. The decrease in measured mean wind speed and the increase in turbulence intensity resulting from the bridge deck disturbance is considered to restore the actual wind parameters. Finally, the joint probability distribution model is developed using the Gaussian Copula function. The results demonstrate the efficacy of the proposed method in mitigating the bridge deck disturbance on field measurements, thereby establishing accurate and reliable probability distribution models. • Irregular distribution of field measurements of a long-span bridge is discovered. • Effects of the bridge deck disturbance on field-measured wind data are analyzed. • A novel method is proposed to remove disturbed components from field measurements. • A joint distribution model of mean wind speed and turbulence intensity is built. [ABSTRACT FROM AUTHOR]

In the service period, coastal bridges are suffered from wind, wave, and environmental actions, which is a high-risk meteorological environment. To investigate the safety and comfort of vehicle-bridge subjected to the combined wind and wave, Copula-coupled theory is employed to discriminate the statistical correlation from wind speed (U w) to wave height (H s). According to the measured data, the combined values in different bivariate return period (BRP) are obtained by the optimal joint distribution (e.g., Clayton Copula). Wind forces on vehicle-bridge system involved buffeting and statical are considered. The wave forces of substructure are derived by Morison and MacCamy-Fuchs equation. A presentative double pylon cable-stayed bridge is employed to explore the effect of wind and wave loads. The vehicle-bridge dynamic response increases as the increase of BRP, especially the lateral displacement of mid-span, which is mainly affected by the first-order transverse bending fundamental frequency of the bridge. All dynamic response indexes meet the standard value. • Copula-coupled model is applied to identify the correlation between wind speed and wave height. • The wind-wave combined values in different bivariate return period (BRP) are obtained by the optimal joint distribution. • The vehicle-bridge dynamic response in different BRPs are calculated and analyzed. [ABSTRACT FROM AUTHOR]