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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]

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]

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]

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]

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]

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

This 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]

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]

• 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]

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]

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]

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]

• 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]

• 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]

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]

Typhoon winds near the external eye wall of a strong typhoon are extremely nonstationary and disastrous due to its vortex and convective origin as well as its high wind speeds. However, typhoon-induced nonstationary responses of long-span bridges are currently analyzed with the assumption of time-invariant wind coherence. By taking the Stonecutters cable-stayed bridge in Hong Kong under Typhoon Hato in 2017 as an example, this paper presents the time-varying wind spectra and coherences for the bridge based on the wind data recorded by the multiple anemometers installed on the bridge. The analytical framework for nonstationary buffeting analysis of long-span bridges under typhoon winds is enhanced by considering time-varying wind coherence and applied to the Stonecutters Bridge under Typhoon Hato. The computed responses are compared with the field measurement responses. The comparative results demonstrate the feasibility and accuracy of the enhanced framework for buffeting analysis of long-span bridges with time-varying wind spectra and coherences. Comparative results with the other two cases of time-invariant coherence functions also highlight the importance and necessity of considering the time-varying wind coherence in the nonstationary buffeting analysis of long-span bridges under typhoon winds. [ABSTRACT FROM AUTHOR]

In order to analyze the influence of the stiffness change of the long-span track bridge on running safety of the train, a bridge and train analysis model, based on Chongqing Egongyan track bridge, is established to simulate and evaluate the spatial coupling dynamic response of the wind–train–bridge system through stiffness change and to propose the reasonable stiffness limit range of the long-span track suspension bridge. The results show that the dynamic characteristics of the bridge are good, and the safety of train operation and ride comfort meet the requirements when the vertical stiffness is 1/300–1/500 and the lateral stiffness is 1/600–1/1200; the dynamic response of the bridge and the running safety of the train are significantly sensitive to the stiffness change of the bridge, especially when the wind speed is 25 m/s and the vertical stiffness is 1/300, at this time, the derailment coefficient and the wheel load reduction rate reach 0.72 and 0.54, respectively, which are close to the limit standard, indicating that there are some potential safety hazards in train operation. [ABSTRACT FROM AUTHOR]

Six years of wind data are used to investigate the statistical characteristics of general and strong winds acting on the Donghai Bridge, a sea-crossing bridge in China. The general wind at the bridge site shows a relatively stable annual repeatability, and the discrepancies are found between the measured wind field parameters and those suggested by the design code. For strong winds, both the 10-min mean wind speed and the turbulent variance greatly exceed those of general winds, while the turbulence intensity, integral length scale, and gust factor do not exhibit any noticeable quantitative trends. The measured wind spectra of both general and strong winds show a shift toward the high-frequency range compared with Simiu's spectrum (along-wind direction). The wind measurements at the bridge site are easily interfered with the bridge structure itself, resulting in a greater turbulence along the bridge axis and a higher turbulent kinetic energy in the high-frequency range, which needs to be considered in designing structural health monitoring systems in the future. This study provides field evidence for the wind-resistant design and evaluation of long-span sea-crossing bridges. [ABSTRACT FROM AUTHOR]

The purpose of this study is to investigate the flutter control scheme of super long-span bridges with various aspect ratios (e.g. width to height (B/H)) using passive aerodynamic countermeasures. Through a series of wind tunnel testing and theoretical analysis, three types of passive aerodynamic countermeasures, i.e. vertical central stabilizer (VCS), wind barrier and inspection rail, were investigated for five typical aspect ratios of a closed-box girder bridge. The results show that both the aspect ratio and flutter critical wind speed generally increase with the decrease of the ratio of torsional and vertical frequencies of the bridge. In the case of an aspect ratio of 8.9, a downward VCS (DVCS) has a much better flutter performance than that of an upward VCS (UVCS) because aerodynamic damping of Part A and Part D could produce a higher heaving degree of freedom (DOF) participation level. Furthermore, the position variation of wind barriers is superior to their shape variation for the bridge with an aspect ratio of 8.3, and the flutter performance of the girder with a combination of the wind barrier (WB3P3) and UDVCS with 0.3 h/H DVCS appears to be better than that without countermeasures. In addition, the installation of an inspection rail near the bottom point of an inclined-web (IR3) has the best flutter control effect among four positions of inspection rails. [ABSTRACT FROM AUTHOR]

PM 10 pollution is a pressing ecological concern within arid and semi-arid cities, adversely influencing the natural environment and human health. Based on the Geographically and Temporally Weighted Regression (GTWR) model, this study comparatively investigated the spatiotemporal dynamics of PM 10 during non-dust and dust periods in five arid cities (Jiuquan, Jiayuguan, Zhangye, Jinchang, and Wuwei) and one semi-arid city (Lanzhou) in northwest China. Further, this study examined the critical mechanisms of PM 10 via the GTWR and Geographic Detector model. A comparative analysis illustrated that dust period PM 10 concentrations surpassed non-dust period concentrations. The annual average PM 10 concentrations during the non-dust period wavily declined from 2015 to 2020, exhibiting significantly higher levels in the semi-arid city as opposed to arid cities. Conversely, during the dust period, PM 10 levels rose initially between 2015 and 2017 and diminished from 2018 to 2020, with high concentration clusterings primarily observed in 2015–2016 in western arid cities, Jiuquan and Jiayuguan, in 2017–2019 in eastern cities, Wuwei and Lanzhou, and in 2020 in central arid cities, Jinchang and Zhangye. During the non-dust period from 2015 to 2020, the cumulative effects of single driving factors were ranked in the following order: soil moisture content (MOI), geographical location (LOC), precipitation (PRE), SO 2 , gross domestic product (GDP), wind speed (WS), and digital elevation (DEM) while during the dust period, the emphasized factors were ranked in the following order: MOI, LOC, PRE, WS, SO 2 , GDP, and DEM. The interaction between MOI and WS on PM 10 was most noticeable in this study (non-dust: 0.787, dust: 0.832). Thus, MOI and WS are critical components in controlling PM 10 pollution. The outcomes of this study can furnish theoretical foundations for ecological construction in Northwest China, unlock novel insights for ecological measures in other global arid and semi-arid cities. [Display omitted] • PM 10 concentrations showed an overall downward trend from 2015 to 2020. • During non-dust period, high PM 10 concentrations mainly distributed in semi-arid city. • During dust period, high PM 10 concentrations mainly distributed in arid cities. • MOI, LOC, and pre are the three most dominant single drivers of PM 10. • The interaction of MOI and WS strongly affected PM 10 concentrations. [ABSTRACT FROM AUTHOR]

• The Hilbert spectrum-based method and the two-dimensional (2D) indicial response function was introduced in the time domain buffeting analysis of a long-span bridge under nonsynoptic events. • The downburst wind presents significantly nonstationarity characterized by time-varying mean and spectrum, while slightly nonstationary nature was observed in the typhoon events. • The downburst-induced transient effects on the indicial response function, aeroelastic loads and buffeting response were highlighted, while negligible transient effects were observed under typhoon events. Inherent nonstationarity of the wind speed records is frequently captured during downburst and typhoon events, however, the significance of nonstationary effects on the bridge aerodynamics has not been widely investigated yet. In this study, the nonstationary wind-induced effects on aerodynamics under downburst and typhoon events were discussed. More specifically, the wind field input was generated using the instantaneous information embedded in the Hilbert spectrum, which was extracted from full-scale measurements of downburst and typhoon wind. The two-dimensional (2D) indicial response function was employed in the time domain buffeting analysis of a long-span bridge, and the transient effects on the bridge aerodynamics under downburst and typhoon were discussed. The results from the present study highlighted the significant transient nature of the downburst wind and its transient effects on the indicial response function, aeroelastic loads and buffeting response, while negligible transient effects under typhoon events. [ABSTRACT FROM AUTHOR]

• A neural network-based model (Buffeting-Net) is proposed to predict buffeting response of full-scale bridges. • Inspired by the mechanism of buffeting, the model is composed of two sub-neural networks. • Buffeting-Net can make more accurate predictions for full-scale bridges than FEM-based buffeting theory. In order to predict power spectral density (PSD) and root of mean squares (RMS) of buffeting responses of full-scale bridges in real operation conditions, a neural network-based model in frequency domain (Buffeting-Net) is proposed. Inspired by the mechanism of buffeting, the model is composed of two sub-neural networks that output the buffeting force and the generalized frequency response function. These two sub-neural networks are connected according to the model of buffeting response in the frequency domain to output the predicted spectrum of response. Sub-neural networks are constructed by bi-directional gated recurrent unit neural networks for their capacity of modeling complex mappings among sequences. Monitoring data of two long-span bridges are used for model validation, and the accuracy of prediction is evaluated by the cosine similarity of the shape of power spectrum and the relative error of RMS responses. The prediction results of Buffeting-Net are also compared with the traditional FEM-based buffeting method. The results indicate that trained models can make much higher accurate predictions for the bridges in real operational conditions including typhoon and season wind than regular finite element model-based buffeting analysis method. The generalization of the Buffeting-Net is validated, the result indicates the Buffeting-Net can predict the buffeting response with high prediction accuracy even when the wind speed is much greater than that in training. [ABSTRACT FROM AUTHOR]

• A framework for long-term extreme buffeting response estimation based on Monte Carlo simulations is proposed and was applied for the first time to a long-span suspension bridge in the design phase. • Extreme buffeting response of a long-span bridge was estimated with long-term frameworks and compared with current design guidelines. • Results indicate that the current design guidelines may underestimate the extreme buffeting response of long-span bridges. • The proposed framework showed to be more accurate and less computationally demanding than the other available long-term frameworks. Several studies have shown that site measurements of the buffeting responses of long-span bridges do not always agree with predictions from analytical models. The observed discrepancy is believed to be explained by the variability in the wind's turbulence field, which is ignored in the current design guidelines. Additionally, the guidelines neglect the true variability in the buffeting response, as this parameter is considered to be deterministically dependent on the mean wind speed only, and a single short-term-averaged wind condition is assumed to be representative of the bridge's behaviour over its lifetime. Such assumptions underestimate the design buffeting response. Alternatively, a full long-term analysis is regarded as the most accurate approach to handling extreme response estimations. Applications of this analysis in the wind engineering literature are scarce due to its large computational demand. With the objective of alleviating such demand, this paper proposes a full long-term analysis framework based on importance sampling Monte Carlo (ISMC) simulations and investigates, for the first time, the extreme buffeting response of a suspension bridge in its design phase with this framework. The results were compared with available formulations based on reliability methods and numerical integration. The proposed ISMC framework requires fewer simulations than the other formulations while maintaining a good degree of accuracy. The results show that the estimated extreme response is 30% larger than the current design guidelines suggest, showing the importance of considering the turbulence parameters' and loading effects' variabilities when calculating extreme responses. [ABSTRACT FROM AUTHOR]

The present study investigated the problem of increasing the critical flutter wind speed of long-span bridges by using tuned mass dampers (TMDs) on both theoretical and experimental aspect. The governing equations of motion of a bridge deck with TMD are analytically formulated. The method of step-by-step flutter analysis is improved and extended from the 2-DOF model to the 4-DOF model to calculate the critical flutter wind speed and parameters of TMD. A sectional model wind tunnel test is carried out to examine and validate the numerical results, and some new findings from the obtained results are included. [ABSTRACT FROM AUTHOR]

In order to estimate wind-induced fatigue damage, most methods use the probability density functions of wind speed and direction. Conventional approaches assume that these functions are error-free and provide a single estimated damage value. However, the estimated damage may contain significant errors because the probability density functions are generally inexact, and the parameters for the functions rely on limited measured data. We propose a Bayesian approach to determine the fatigue damage while considering the uncertainties in the probability model and the parameter. The proposed approach provides a distribution of damage values, which enables more comprehensive analysis of fatigue damage using bounds and exceedance probability. The approach is applied to the estimation of fatigue damage of long-span bridges. We also illustrate an additional feature of the Bayesian approach, which is to systematically update the damage index as more measurements become available over time. Effect of data size is investigated to quantify the error due to the limited measured data. The influence of uncertainties in other parameters and effects of long term wind speed variability is also included in this study. [ABSTRACT FROM AUTHOR]

• Multiple-fan active control wind tunnel tests were performed to investigate the wind effects of a long-span rigid-frame bridge subjected to short-rise-time gusts. • The gust parameters in mountainous areas have significant impacts on the rigid-frame bridge. • The occurrence of the impact effect is related to the gust acceleration. • The flange slab has better mitigating effects for the impact of gusts on the rigid-frame bridge with bluff body cross section. Short-rise-time gusts in mountainous areas are extreme winds with the characteristics of rapidly varying wind speeds and directions, strong suddenness, and large angles of attack. Currently, studies on long-span bridges under short-rise-time gusts in mountainous areas, especially experimental studies, are limited. In this study, a typical long-span rigid-frame bridge with a bluff body girder located in a mountainous area suffering from frequent gusts was selected. Corresponding sectional and full aeroelastic model tests in a multiple-fan active control wind tunnel were performed to investigate the aerodynamic forces and wind-induced responses under strong gusts. Two aerodynamic measures (i.e., flange slab and stabilizing plate) were applied to mitigate the impact of gusts on the studied bridge. Moreover, numerical simulation analysis was also carried out to investigate the effects of gusts on the wind-induced stresses. The experimental results demonstrated that the gust parameters significantly affect the aerodynamic forces and wind-induced responses of the long-span rigid-frame bridge, especially under construction, although this type of bridge usually shows less wind-related sensitivity under normal monsoon climates. Furthermore, the proposed aerodynamic measures effectively mitigated the displacement responses of the studied bridge subjected to gusts in mountainous areas. This investigation can provide a more comprehensive understanding of the aerodynamics and aeroelastic performance of similar bridges under gusty conditions. [ABSTRACT FROM AUTHOR]

• Probabilistic vortex-induced vibration (VIV) occurrence prediction based on wind tunnel tests. • Prediction of the vortex-induced vibration occurrence using decision tree method. • Considering the effects of structural damping ratio, wind direction and wind speed. • Probabilistic cost-benefit analysis from Aerodynamic countermeasures (ACMs) application. The twin-box girder is a recommendable structural style for long-span cable-supported bridges due to its excellent aeroelastic stability. Vortex-induced vibration (VIV) is a typical wind-induced vibration for this kind of girder with a high occurrence probability associated with wind characteristics, structural properties and aerodynamic configuration under uncertainty. Therefore, probabilistic approaches should be adopted to predict the occurrence of VIV under uncertainty. This paper presents such an approach to predict the VIV occurrence using the decision tree method. Wind tunnel tests on a large-scale section model are conducted to investigate the effects of structural damping ratio and wind speed on VIV performance. Uniform and turbulent wind flow fields under three attack angles of −3°, 0°, and −3° are tested. Moreover, wind direction at the bridge site is determined as a parameter affecting VIV occurrence. As a result, a decision tree considering the effects of structural damping ratio, wind direction and wind speed is formulated to estimate the probability of VIV occurrence. In order to suppress VIV, aerodynamic countermeasures (ACMs) with L-shaped windshields are applied. Furthermore, the probabilistic cost-benefit analysis of the application of ACMs is developed using a decision tree, and the probability of the positive cost-benefit from ACMs application is accordingly estimated. The application of the proposed probabilistic approach is investigated on a long-span cable-stayed bridge with two separated steel boxes. [ABSTRACT FROM AUTHOR]

• A framework for analyzing the tropical-cyclone-induced flutter failure reliability of long-span bridges is developed. • Uncertainties of bridge dynamic characteristics and aerodynamic parameters are quantified. • The tropical-cyclone-induced wind hazard curve of at the height of the bridge deck is achieved. • The tropical-cyclone-induced flutter failure reliability of a suspension bridge is investigated. Continuously growing number and span length of long-span bridges in coastal region of China require a robust aeroelastic design to against the tropical-cyclone (TC) -induced flutter instability. Instead of using the deterministic approach, this study presents a Monte-Carlo-technique-based framework to analyze the flutter reliability of a long-span suspension bridge subjected to TC winds. A limit state function formulated as the difference between the flutter capacity and the extreme gust wind, termed as the product of a random gust factor and the TC mean wind hazard is employed. The flutter fragility curve in terms of the critical wind speed is derived using 2D and 3D flutter analysis models accounting for the structural modal and damping randomness as well as experiment-induced errors of aeroelastic flutter derivatives. The TC wind hazard curves at the height of the bridge deck described as the probability of exceedance at any given years of interest versus the extreme 10-min mean wind speed are estimated through generating a large quantity of synthetic tracks around the bridge site. The probabilistic solutions of the gust factor associated with any gust duration of interest are determined utilizing the statistics of observed TCs coupled with a theoretical model. The TC-induced flutter failure probabilities of present bridge are then predicted in different combinations of gust duration, surface roughness length and flutter analysis models, which enables the assessment of flutter risk subjected to TC winds as compared to code-suggested target reliability indices. The present reliability analysis provides some basic information to assist and enhance the flutter-resistant design of long-span bridges due to TC winds during the preliminary stage. [ABSTRACT FROM AUTHOR]

To explore the influence of bridge wind barriers, with their specific opening shapes and arrangements, on bridge deck wind fields and vehicle driving stability under different crosswinds, five bridge wind barrier schemes were designed. For two incoming wind speeds, the wind speed at different heights over three traffic lanes and the aerodynamic six-component force of the vehicle model were measured, and the influence of the wind barrier parameters on the vehicle driving stability was analyzed. The equivalent wind speed reduction coefficient of the wind barrier was compared with the dimensionless coefficients of the aerodynamic side force, roll moment, and aerodynamic lift to verify the accuracy of the shielding effect evaluation indices. The final conclusions provide a useful reference for designing bridge wind barriers. [ABSTRACT FROM AUTHOR]

• A refined joint model of wind speed and direction is proposed. • An assessment method of fatigue lifespan considering the variations in traffic and the wind load is developed. • The fatigue lifespan of a stay cable on the windward side is relatively short. Stay cables are crucial load-bearing components of long-span cable-stayed bridges. Because they are sensitive to wind, the wind load is an important control load in their safety and fatigue evaluation. To consider the effects of variations in the wind speed and direction, a joint probability density model of wind speed and direction is proposed for evaluating the fatigue lifespan of a stay cable. For this purpose, an angular–linear model is introduced to coordinate the marginal distribution of wind speed and direction. The marginal distribution of wind speed comprises a Gumbel model, while that of the direction comprises a refined mixture of a von Mises distribution model. Subsequently, based on the dynamic simulation of a coupled wind–vehicle–bridge system, an assessment method for fatigue lifespan is developed by considering the variation of traffic flow with four load levels and variations in wind speed and direction. The results indicate that the refined angular–linear distribution model yields considerable fitting results for the measured data with respect to the wind speed and direction. Although the response and fatigue damage of a stay cable mainly depend on its length and location, the effect of the direction variation of the wind load is also not negligible. Additionally, the results from the assessment method show that the fatigue lifespan of a stay cable on the windward side of the local prevailing wind direction is relatively shorter than that of the leeward side. [ABSTRACT FROM AUTHOR]

This paper presents a computationally efficient method for the conditional simulation of nonstationary fluctuating wind speeds for the buffeting analysis of long-span bridges. The fluctuating wind speeds, with part of their time histories measured at some points, are regarded as a zero-mean nonstationary Gaussian vector process characterized by an evolutionary power spectral density (EPSD) matrix. The Kriging method is then applied to the random vector of the Fourier coefficients of the evolutionary vector process for conditional simulation. A mathematical proof of this conditional simulation is provided. A fast algorithm of the conditional simulation is further derived, by converting the Cholesky decomposition of a large size covariance matrix of the Fourier coefficients into the Cholesky decomposition of a series of small-size coherence matrices with much less computational time. The procedure for implementing the fast algorithm-based conditional simulation method is detailed. Finally, this method is applied for the conditional simulation of typhoon-induced nonstationary wind speed time histories for the buffeting analysis of Stonecutters Bridge in Hong Kong. The time domain buffeting responses of the bridge obtained using the conditionally simulated wind speed time histories indicate that the proposed simulation method is feasible and applicable. [ABSTRACT FROM AUTHOR]

• A novel framework is proposed for bride buffeting analysis with insufficient wind data. • LSTM network and nearby measured data are used to compose necessary data. • A suspension bridge under construction is adopted to demonstrate performance. Buffeting analysis of long-span suspension bridge has received considerable attention in the past decades. In current practice, it is challenging to determine the wind turbulence spectrum at bridge site accurately if the field measured wind data is insufficient. To address this issue, this paper proposes a novel framework for bridge buffeting responses evaluation. The framework first proposes an approach based on long short-term memory (LSTM) network to compose long term data on wind characteristics for estimating the wind turbulence spectrum at bridge site via leveraging the wind field data acquired from the long-term monitoring data at adjacent locations (e.g., nearby meteorological station and bridges). Afterwards, the obtained wind spectrum at bridge site will be utilized for the buffeting analysis. To demonstrate the usage and performance of the proposed framework, a long-span cross-sea suspension bridge under construction is used throughout the paper as an example to investigate the buffeting-induced responses. The analysis results show that buffeting responses are significantly affected by wind speed and the identified bridge frequencies are consistent with the design frequencies. [ABSTRACT FROM AUTHOR]

Flexible bridges could experience vortex-induced and buffeting excitations below their design wind speeds and divergent self-excited oscillations (flutter) beyond a critical wind speed. For regular straight-line winds that are stationary or weakly stationary, a frequency domain formulation is routinely used for flutter analysis of bridges. However, when evaluating performance of flexible bridges subjected to gusty winds that are transient in nature, the frequency-domain formulation is not applicable, and hence time-domain methods should be used. In this paper, time-domain formulations were used to predict aeroelastic loads acting on a rigid bridge deck section model subject to stationary and gusty straight-line winds based on the knowledge of upstream wind speed and model displacement measurements. In this procedure, rational functions and indicial functions are used to formulate self-excited forces and buffeting forces, respectively. The functions used here were recently obtained from wind tunnel tests performed on a streamlined bridge deck section model with a smaller geometric scale. The results of the validation using a larger section model of this bridge deck subject to a ramp-type gust are presented here. [ABSTRACT FROM AUTHOR]

Abstract: We study the aerodynamic control of long-span suspension bridges and seek to raise the critical flutter wind speeds, while simultaneously suppressing buffeting. The control system design study is based on a simple flexible bridge section model that interacts with a constant-velocity air stream. A streamlined bridge deck is assumed and non-steady thin aerofoil theory is used to describe the interactions between the bridge deck and the air stream. Classical turbulence models, first developed in the aircraft industry, are used to model the buffet forces acting on the deck. While a wide variety of control systems is possible, we focus on a compensation scheme that can be implemented using passive mechanical components such as springs, dampers and a rack and pinion mechanism. A single-loop control system is investigated that controls a trailing-edge flap by sensing movements of the bridge deck; several such mechanisms are contemplated. The first finding is that the critical wind speed for flutter can be greatly increased, with good robustness characteristics, through passive feedback control. It is also possible simultaneously to suppress flutter using the same passive mechanical controller by solving a passive mixed control problem. The effect of flexible controller mounting arrangements are considered briefly. [Copyright &y& Elsevier]

• Extension of LU model to Volterra model improves the buffeting analysis results. • Nonlinearity and non-stationary wind effects are critical to the bridge response. • Non-stationary wind effects can be characterized by the time-varying mean wind. • Time-varying mean wind speed causes the time-varying mean response of the bridge. • Aerodynamic nonlinearity effects may become significant at high wind speeds. This paper presents a nonlinear time-domain analysis framework to simulate the buffeting response of long-span bridges subjected to the typhoon winds. The analysis framework separates the aerodynamic forces generated on the bridge deck into low- and high-frequency components modelled by the quasi-steady and Volterra series-based wind load models, respectively. The aerodynamic nonlinearity and non-stationary wind effects existing in the wind-bridge interaction are incorporated in the analysis framework in terms of the ① static force coefficients measured at low-frequency effective angle of attack, ② flutter derivatives identified at varying angles of attack, ③ higher order fluid memory terms of the Volterra series and ④ time-varying mean wind speed. The efficacy of the proposed framework is verified by presenting the numerical example of a suspension bridge fully immersed in the typhoon winds with aerodynamic characteristics sensitive to the effective angle of attack. The dynamic analysis results show good agreement in the simulation of the typhoon-induced buffeting response of the bridge deck. Moreover, the simulation results are also compared with the measurements, and the existing linear and nonlinear wind load models to elucidate the efficiency of the proposed framework. [ABSTRACT FROM AUTHOR]

• A novel aerostatic stability analysis method using a modal formulation is presented. • Convergence to the critical wind velocity is accelerated through a root-finding algorithm in the outer loop. • The proposed method is applied to a cable-stayed bridge considering multiple nonlinear features. • The collapse is driven by stiffness degradation due to stays loss of tension and ultimately stiffness. • The influence of aerodynamic and structural nonlinear features on the critical wind velocity is investigated. An efficient method for analyzing the nonlinear aerostatic stability of long-span bridges using a modal formulation is proposed. First, a simplified linear version defined as modal-based approach is introduced, which evaluates the bridge displacements using the modal properties of the bridge and speeds up the assessment of the critical velocity by applying a root-finding algorithm. Then, this scheme is further developed to identify the instability limit point in nonlinear structures by combining nonlinear FEM analyses with the linear version of the modal-based approach and a root-finding algorithm in an outer loop. The effects of considering the three components of the wind loads, the stays sag effect, structural nonlinearities, aerodynamic nonlinearities, and the initial wind angle of attack, are analyzed and discussed. The computational advantages of the proposed method and its accuracy are demonstrated through three application examples, including a simplified linear 1 DoF system, and linear and nonlinear FEM models of a full cable-stayed bridge. The collapse mechanism of the cable-stayed bridge is driven by the stiffness degradation of the stays caused by the deck vertical upward displacements. It has been found that the influence of the nonlinear aerodynamic features is very low when the structural nonlinearities control the bridge collapse. [ABSTRACT FROM AUTHOR]

As the aviation industry has entered a critical period of development, the demand for Automatic Dependent Surveillance Broadcast (ADS-B) technology is becoming increasingly urgent. Real-time detection of aviation wind field information and the early warning of wind field shear by atmospheric sounding system are two important factors related to the safe operation of aviation and airport. According to the advantages of ADS-B and Mode S data, this paper uses the Meteo-Particle (MP) model proposed by Sun et al., in their previous research to retrieve high-altitude wind field. Comparing the precision and accuracy of wind field retrieved results, and the optimization parameters of MP model suitable for meteorological model are further studied. To solve the problem of incomplete wind field coverage obtained by retrieval, an extrapolation algorithm of wind field is proposed. The results show that: (1) a comprehensive evaluation index is introduced, which can more effectively evaluate the comprehensive difference of wind field retrieval results in wind speed and direction. (2) The adaptability results of MP model in different periods and altitudes provide some reference for the research of other scholars. (3) The new parameter setting can improve the accuracy of the retrieved results, and the appropriate extrapolation of wind field fills in the blank part of aviation and meteorology. [ABSTRACT FROM AUTHOR]

• A gyroscopic stabilizer is studied to reduce propensity to long-span bridge flutter. • Frequency-domain simulations at incipient aeroelastic instability are performed. • Significant increment of critical flutter speed is noticed. Long-span cable-supported bridges are gaining considerable importance in the world. It is generally recognized that long-span cable-supported bridges can be very sensitive to wind effects due to their aerodynamic properties and deck flexibility. Flutter is usually a major concern because it can lead to structural deck failure. This communication introduces a prototype of gyroscopic device as an active stabilizer for improving flutter performance. A mathematical model of the gyroscopic device, installed at the bridge deck level, was studied and implemented to assess its effectiveness in increasing the critical wind speed. A preliminary study was conducted to evaluate the stabilizer's performance on a benchmark long-span cable-supported bridge as a function of its gyricity. The results demonstrate that the gyroscopic stabilizer is very successful and bridge flutter threshold increases with the gyricity of the gyroscopic device, within a practical operational range. [ABSTRACT FROM AUTHOR]

• Turbulence variability strongly affect the response of long-span suspension bridges. • The environmental contour method (ECM) can describe design storms for bridges. • The ECM was able to predict the scattered full-scale measured bridge response. • The ECM gave up to 60% increased design response compared with the current practice. Full-scale monitoring of the Hardanger Bridge has revealed significant turbulence-induced variability in the measured acceleration response. In this paper, a probabilistic model is used to describe the uncertain turbulence parameters, and the environmental contour method is used to investigate the long-term root-mean-square (RMS) response of the Hardanger Bridge. The results show that turbulence-induced variability has a significant impact on the bridge girder section moments. It is also interesting that the critical combination of environmental parameters does not necessarily involve the maximum mean wind velocity. By using the environmental contour method to account for turbulence uncertainty, the scattered acceleration RMS response measurements from the Hardanger Bridge are successfully eclipsed by 100-year return period response estimates, showing vast improvements compared with the traditional design methodology. The investigations presented in this paper show that the environmental contour method can be used to improve the accuracy and reduce the uncertainty in buffeting response calculations for long-span bridge design. [ABSTRACT FROM AUTHOR]

The complex wake-induced vibrations (WIVs) of four aligned hangers behind a bridge tower were numerically simulated. The aligned hangers were simplified to two-dimensional spring–mass–damperdynamic models, and the hanger collisions were described with a rigid impact model. The Newmark - β method was employed to calculate the hanger oscillations with the user-defined function embedded in the numerical Computational Fluid Dynamics (CFD) simulations. The flow fields around the bridge tower for various yaw angles were simulated first to analyse the wake velocities at the hanger point. Subsequently, the characteristics of the hanger vibrations and the correlations between the hanger vibrations and tower wake were studied. The mechanism of the hanger collisions was revealed by analysing the differences between the aerodynamic coefficients of the hangers. Finally, the changes in the characteristic size of the tower and incoming wind speed were investigated to explain the occurrence of the violent WIVs of the hangers behind the bridge tower. [ABSTRACT FROM AUTHOR]