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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]

The local wind environment above the bridge deck affects the aerodynamic characteristics of vehicles, thus affecting the driving safety of the bridge deck. Influenced by the mountain topography and the bridge deck's ancillary facilities, the local wind environment above the bridge deck is complex and changeable, and its impact on the bridge deck traffic can not be ignored. In order to accurately evaluate the local wind field parameters, a monitoring system of the local wind environment is developed. Utilizing the monitoring system, wind parameters above the approach deck of a long-span suspension bridge in a mountain area are measured. The relationship of wind characteristics between the incoming flow and the wind above the bridge deck is investigated. Results show the significant difference between the local wind environment above the bridge deck and the incoming flow's characteristics; the wind profile above the bridge deck does not follow the exponential distribution; the equivalent height of the wind load on the vehicle is higher than the vehicle's gravity centre. This study is relevant for studying the local wind environment, driving safety, and serviceability of long-span bridges in mountainous areas. [ABSTRACT FROM AUTHOR]

This study revisits the modeling of buffeting forces on bridge decks and establishes the relationship between one- and two-wavenumber admittances, and between the spanwise coherence functions of turbulence and buffeting forces. The two-wavenumber admittance of the lift of a thin, flat plate section caused by vertical turbulence is then used to investigate the three-dimensionality effect of turbulence on integrated buffeting lift of a finite length. To investigate the characteristics of two-wavenumber admittance of bridge deck sections, synchronous pressure distributions of a streamlined bridge deck are measured and characterized in a wind tunnel at three different turbulent flows and several angles of attack. The means and standard deviations of surface pressure coefficients and integrated drag, lift and moment coefficients, the power spectra, spanwise correlation, and coherence of turbulence and buffeting forces are analyzed, from which the two-wavenumber admittances of drag, lift, and moments are determined. The effects of integral length scale and intensity of turbulence and angle of attack on static force coefficients and admittances are characterized. Finally, the three-dimensionality effect of turbulence on integrated buffeting forces and responses of long span bridges are investigated using the measured two-wavenumber admittances. The results of this study highlight the importance of appropriate simulation of large-scale turbulence in wind tunnel for characterizing static force coefficients and admittances of bridge deck sections, and for estimation of buffeting responses 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]

The newly-built single-level rail-cum-road bridge brings the issue of the aerodynamic impact of train-induced wind on road automobiles. This research introduced a validated computational fluid dynamics (CFD) model regarding this concern. Such an aerodynamic impact mechanism was explored; a relationship between the transverse distance between train and motor-van (hereinfafter referred to as van) and the aerodynamic effects on the van was explored to help the optimization of bridge decks, and the relationship between the automobile speed and aerodynamic variations of a van was fitted to help traffic control. The fitting results are accurate enough for further research. It is noted that the relative speed of the two automobiles is not the only factor that influences the aerodynamic variations of the van, even at a confirmed relative velocity, the aerodynamic variations of the van vary a lot as the velocity proportion changes, and the most unfavorable case shows an increase of over 40% on the aerodynamic variations compared to the standard case. The decay of the aerodynamic effects shows that not all the velocity terms would enhance the aerodynamic variations; the coupled velocity term constrains the variation amplitude of moments and decreases the total amplitude by 20%–40%. [ABSTRACT FROM AUTHOR]

The buffeting analysis of an uncertain long-span bridge deck was carried out in this paper. Due to the effect of strong spatial correlation of wind excitation, it should be assumed as partially coherent multiple excitations. The following includes a theoretical formula for the buffeting analysis of a long-span bridge deck with uncertain parameters, which was achieved mainly by a combination of the stochastic pseudo excitation method (SPEM) and response surface method (RSM). The SPEM-RSM was firstly applied to deal with the complicated spectral density function matrix of wind excitation. The buffeting response of the bridge deck was then calculated and verified by the results from the Monte Carlo simulation (MCS). The efficiency and applicability of the hybrid method for strong spatial correlation was proved. After the comparison, the effect of uncertain structural parameters and wind speed on the buffeting performance of the bridge deck were computed. The results showed that the whole uncertainties essentially affected the buffeting response of the deck. The uncertain wind speed played the most significant role in the vertical and lateral motion of the deck. The joint influences between structural uncertainties and uncertain wind speed further affect the random characteristics of the responses. Finally, the effects of different wind speed and wind angle of attack on the aerodynamic performance of the bridge are examined. The variance of the responses increased with the development of wind speed. The effect of different attack angles on the buffeting responses was significant. [ABSTRACT FROM AUTHOR]

To study the impact coefficient of track beams due to moving suspended monorail vehicles under the bridge deck, this paper presents a vehicle-bridge dynamic model based on the rigid-flexible coupling method. Finite element method is used to establish the bridge model, and the vehicle is simulated as a multi-body dynamic model The mechanical characteristics of running tire are precisely modelled and the dynamic equations for the suspended monorail vehicle-bridge coupling system are derived. The proposed approach employs a double-line 7-span bridge with 210 m length as a numerical example, the impact performance of two track beams are studied and the results are verified by comparing with the theoretical solutions. The influences of critical system parameters, such as the train formation and double-line trains loads, on the dynamic responses of vehicles and the bridge are explored. The results show that it is feasible to study the impact effect with the proposed method. The separation phenomenon of rubber running tires jumping up on track surface occurs when vehicle speed is high, which may lead to negative impact coefficients. The impact coefficients of the track beam vary much with different locations, which can even be negative values at locations nearing the pier area. [ABSTRACT FROM AUTHOR]

The aerodynamic performance of vehicles on a bridge deck depends on the local wind field, especially in a region near a bridge tower. This study was carried out on a large-scale (1: 20.4) truss girder, and wind tunnel tests were performed to determine how the wind fields were affected by the bridge tower in the presence of different wind barriers. The wind barrier parameters significantly affect the wind field. Wind barriers should be sufficiently high to provide a wide protection range and have relatively small porosities to reduce the wind speed. The opening form of the wind barrier should also be considered, where a circular-holed form reduces the wind speed and turbulence more than a horizontal-slatted form. The wind field is affected by structures and bridge towers on the deck. A turning point in the wind speed occurs at a measurement point near the bridge tower, and this point gradually moves upward towards lanes on the leeward side of the bridge. The equivalent wind speed is significantly reduced over a four-meter height range because of shadowing from the bridge tower and the wind barrier. [ABSTRACT FROM AUTHOR]

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

Traffic accidents on bridges occur occasionally and have attracted the wide attention of the whole society as well as world. Therefore, researching and exploring the wind environment on bridge deck is a significant and urgent incident, which is able to provide crucial reference for vehicle driving safety. In this paper, the wind environments on the bridge deck of twin-box girder with large scale of 1:20.4 are investigated through wide-ranging wind tunnel tests. During the tests, multiple wind barriers with different heights, porosities and opening forms are considered precisely. Also, the wind environments of truss girder are studied and compared in the process of experiment. Eventually, after handling with the data, analyzing the figures and comparing with other test results, the most significant disciplines are as follows: The wind environments of twin-box girder and truss girder are fairly various; the power spectrum and the wind velocity of twin-box girder are much larger, and there is a lag at the wind velocity stabilization point of truss structure. At the same time, while the parameters of wind barriers change, lower porosity creates lower wind velocity and lower power spectrum. And the height of the wind barriers affects the wind profiles a lot on the windward lanes and lower power spectrum. In addition, the effects of the opening form on windproof and power spectrum are relatively limited. [ABSTRACT FROM AUTHOR]

For the simulation of fluctuating wind velocity field with n processes, the existing spectral representation method requires a total of n(n+1)/2 executions of the fast Fourier transform (FFT) algorithm. This requirement is found to be computationally expensive for large structures where the number of processes n becomes very large. An efficient spectral-representation-based method is proposed for the simulation of stochastic wind velocity field using Fourier-Stieltjes integral and polynomial decomposition of order q. The proposed approach is very efficient because only q×n executions of the FFT algorithm are required. Numerical investigations involving the simulation of stochastic wind velocities along the deck of a bridge show that the order of the polynomial decomposition q is very small compared to the number of processes n , and more than 50% of computation time can be saved for the simulation of 100 processes. [ABSTRACT FROM AUTHOR]

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

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

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

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

Tsunamis can cause destructive damage to coastal bridges resulting in huge economic losses and human casualties. Different types of countermeasures can reduce the horizontal and vertical uplift forces of tsunami on coastal bridges, thus protecting them from tsunami damage. However, previous studies have mainly focused on a single measure for the bridge deck. This study concentrates on the integrated countermeasure of the fairing and opening holes on typical coastal T-girder bridge deck. The effect of the integrated measure on reducing tsunami forces under different tsunami bore conditions is investigated through experiments and numerical simulations. The optimal fairing shape is also examined using an adaptive machine learning based technique. Results show that: (a) The openings on the bridge deck can effectively reduce the vertical uplift tsunami forces on the T-girder, but will slightly increase the horizontal tsunami forces on it; (b) With installation of the fairing only, the horizontal force on the T-girder can be effectively reduced due to the diversion effect of the fairing; however, in some cases, this measure will adversely increase the vertical uplift tsunami force on the T-girder; and (c) The combination of the fairing and opening-hole countermeasures for tsunami has a favorable mitigation effect on both horizontal and vertical uplift forces applied to the T-girder bridge deck. The mitigation effect increases beneficially with the increase of the tsunami bore wave height for the studied cases. • A combined countermeasure using opening-hole and fairing is proposed for a typical T-girder coastal bridge against tsunami. • The effectiveness of the countermeasure is verified through the tsunami flume experiments and CFD simulations. • A high-resolution numerical flume and adaptive machine learning framework are used to optimize the fairing shape. • The combined countermeasure can effectively reduce both horizontal and vertical tsunami loads. [ABSTRACT FROM AUTHOR]

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