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Determining the extreme wind speed and basic wind speed in mountain areas is the fundamental topic in wind-resistant design for engineering structures. The traditional epochal approach commingles all types of wind's maximum speeds in a hybrid set regardless of their respective distributions. While the mountain wind climate is a typical mixed system that consists of local and synoptic wind events, differences in meteorological mechanisms lead to deviation in their wind speed distribution. Therefore, it is necessary to distinguish the mixed wind speed distribution and calculate the combined extreme wind speed. This study extends the extreme wind speed theory in mixed wind climates to the mountain wind field. The measured mountain wind data are classified into periodic thermally-driven winds caused by local thermal gradient, cooling windstorms driven by cold high pressure, and sudden intense winds caused by severe convection. Their respective distribution parameters are determined through the peaks-over-threshold approach with generalized Pareto distribution, and the combined extreme wind speed concluding all types of wind is obtained. The combined extreme wind speeds considering wind direction and attack angle are subsequently obtained. Results show that the combined value is a conservative estimation in mountain mixed wind climates. [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]

Long-span bridges in mountainous areas are greatly disturbed by wind, and the wind field at the mountain gorge bridge site is extremely complex. Therefore, it is of great engineering significance to accurately evaluate the wind field characteristics of this kind of terrain. In this paper, to enhance understanding of this kind of wind field, the wind field in a mountainous gorge is measured for a long time using wind radar, and the mean wind parameters are statistically analyzed. The results show that the mean wind parameters vary greatly under different wind directions, and the wind speed profile does not meet the power-law model. Therefore, a mixed model suitable for the wind speed profile in a mountainous gorge is proposed. Additionally, GEV distribution and Logistic distribution are found to be suitable for describing the distribution characteristics of wind speed and angle of attack, respectively. In addition, considering the correlation between wind parameters, this paper also constructs the joint probability model of wind speed and angle of attack at different heights by the Copula function. Thus, a combined wind parameters profile model is developed under different exceedance probabilities based on the inverse first-order reliability method (IFORM). This study can provide a reference for the construction of the joint probability model of wind parameters. [ABSTRACT FROM AUTHOR]

To leverage the abundant wind energy resources available in mountainous regions, an increasing number of wind power facilities and associated transportation infrastructure are being constructed in these areas. There are different types of intense winds in mountainous areas and the non-linear characteristics of the different intense winds vary significantly. The periodic thermally-developed winds are the commonly occurring type of intense wind. Based on the comparison of wind characteristics, this research proposes a prediction model for the periodic thermally-developed winds. The research utilizes the Bi-directional Long Short-Term Memory model(Bi-LSTM), which has been optimized by the Bayesian optimization(BO), to predict wind speed. Based on the relationship between wind field characteristics in periodic thermally-developed winds, a regression correction module is proposed using a joint probability model. Additionally, to address the volatility and uncertainty of wind speed, a Gaussian mixture model is employed for probability prediction. The experimental results demonstrate several findings: 1. The BO-Bi-LSTM model accurately and reliably predicts multi-step results for periodic thermally-developed winds in mountainous areas. 2. The proposed correction module, when combined with other models, yields improved wind speed accuracy compared to the uncorrected values. 3. The Gaussian mixture model produces probabilistic prediction results that consider both interval coverage and interval bandwidth simultaneously. 4. The proposed model can successfully predict periodic thermally-developed winds in mountainous areas for practical engineering purposes, resulting in reliable probabilistic prediction outcomes. It is of great significance for the utilization of wind energy resources and the driving safety of vehicles on ancillary structures. [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 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]

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]

The typical U-shaped deep-cut canyon is widely distributed in the western mountainous areas of China, especially in Sichuan province and Yunnan province. The deep-cut canyon has the characteristics of the high drop in elevation, high-temperature difference, and complex wind environment. A 50 m high meteorological mast with a total of eight anemometers was erected in such topography, and a long-span suspension bridge will be constructed in the area where the meteorological mast is located. Based on the long-term monitor data, the wind characteristic parameters including average and fluctuating wind characteristics and coherence between different heights are investigated. The results are as follows. The dominant wind direction which depends on the topography is north–south. The attack angle of wind is mainly less than zero, and its probability distribution obeys the hypothetical Gaussian distribution. Both the increases in height of anemometer and in wind speed reduce the dispersion of the attack angle of wind. The gust factor has a similar change law of attack angle of wind. Turbulence intensities are affected by the height of the anemometer and the wind speed, and they are different from the recommended value of China Codes. In terms of turbulence integral length scale, the value increases with an increase in the height of the anemometer in the same component. The largest value occurs in the longitudinal direction and the smallest occurs in the vertical direction at the same level. The coherence between any two locations is relatively strong, and the longitudinal component is stronger than others. The measured wind power spectrum for longitudinal, lateral, and vertical wind in deep-cut canyon fits the von Kármán model better. [ABSTRACT FROM AUTHOR]

Moving on a bridge, a road vehicle will experience a gusty crosswind caused by the shielding effects of the bridge tower. The corresponding driving safety is affected by several uncertain factors. In this study, a closed-loop driver-vehicle-crosswind (DVC) model is established to obtain the dynamic responses of the vehicle under given driving conditions. The nonlinear tire cornering force, the real driver behavior and the vehicle aerodynamic loads considering the wind shielding effects of the bridge tower can be taken into account. Based on the support vector classifier approach, a probability-based procedure is established to assess the driving risk of a road vehicle passing by a bridge tower under crosswind. A typical two-axle road vehicle passing by a bridge tower is studied as a numerical case. The dynamic responses of the vehicle and driver reaction under two given driving conditions are analyzed by solving the DVC numerical model firstly. Then, the probability-based model is used to assess the driving risk of the vehicle under different driving conditions; the effects of vehicle speed, wind velocity and friction coefficient of road surface on the driving risk are investigated. [ABSTRACT FROM AUTHOR]

Accurate evaluation of wind field characteristics in complex mountainous areas has essential reference significance for the wind-resistant design of bridges. This paper systematically considers the nonstationary characteristics of the wind field, the randomness, and the correlation of average and turbulent wind parameters (TWPs) via the field measurement data. Combined with the C-Vine Copula and inverse reliability method, the joint probability model (JPM) and environmental contour model of wind speed, turbulence intensity, and turbulence integral length are constructed, respectively. Finally, the probabilistic turbulence wind spectrum models are obtained. The results show that the nonstationary characteristics are prominent, and the disturbance by the wind speed threshold is slight; Furthermore, wind speed, turbulence intensity, and turbulence integral length have a strong nonlinear correlation with wind direction preference. Ignoring the influence of wind direction can incorrectly estimate the correlation characteristics between wind parameters (WPs). In addition, the environmental contour model derived from the joint probability model (JPM) of wind parameters (WPs) is far smaller than the extreme combination under a given probability without considering the correlation. It is concluded that the wind spectrum constructed in this paper can provide an essential reference for evaluating uncertainty in the design stage of long-span bridges. • Combined with the measured data, the nonstationarity of the wind field in the V-shaped Canyon is evaluated. • The wind direction preference, randomness, and correlation between different wind parameters are characterized. • Develop a multi-dimensional joint probability model of wind speed, turbulence intensity, and turbulence integral scale. • Construct the environmental contour of wind parameters and compare it with the traditional design method. • Implementation of probabilistic turbulence wind spectrum based on wind parameter environmental contour. [ABSTRACT FROM AUTHOR]

Cold fronts passing through the mountain areas may produce continuous windstorm and cooling processes, potentially impacting the mountain areas' infrastructure. Cooling windstorms belong to the dynamically-driven wind in the mountain wind system. To accurately estimate the wind field parameters of these storms and provide a basis for structural wind resistance design, cooling windstorms should be extracted and analyzed separately from the wind field observation data. Based on the long-term field measurement in complex mountain terrain, a framework for identifying cooling windstorms is established according to temperature and wind speed features. The mean and fluctuating wind parameters of these intense winds are then obtained. Strong nonstationary is detected for cooling windstorms. This paper focuses on the time-varying regularity of fluctuating parameters during intense wind with cooling based on the evolutionary power spectral density. From the perspective of turbulent energy, the basis for selecting the optimal wavelet decomposition levels is put forward when extracting the time-varying mean wind through discrete wavelet transform in the nonstationary wind speed model. This investigation can provide a reference for studying the nonstationary wind field. • A series of windstorms accompanied by continuous cooling were captured through wind observation in mountain terrain. • The identification and classification framework for cooling windstorm events are established. • Cooling windstorms' nonstationary pulsation characteristics are discussed based on the evolutionary power spectral density. • A selection basis for the optimal decomposition level number of DWT is proposed when extracting time-varying mean wind. [ABSTRACT FROM AUTHOR]

The mixed wind climate in mountain terrain includes periodic thermally-developed winds and synoptic winds. The periodic thermally-developed wind is driven by the local thermal and is the most frequent intense wind event in mountain terrain. Based on the long-term multi-point wind data along the main cable of a long-span bridge in a U-shaped canyon, the identification method for periodic thermally-developed wind considering spatial relationships is put forward. The correlation between mean wind speed and temperature, the non-stationarity of fluctuating wind speed, the temporal variation and spatial distribution of wind characteristics, and horizontal coherence are studied. Results show that the local topography affects the wind parameters of periodic thermally-developed wind along the bridge axis; meanwhile, the wind parameters will change periodically in different periods. The inconsistency of wind characteristics in time and space will make the wind load acting on the structure very complex, which should be considered in the wind-resistance design of wind-sensitive infrastructures in mountain terrain. • The strong correlation between mean wind speed and temperature is analyzed. • The identification principle for periodic thermally-developed wind considering spatial relationships are put forward. • The influence of local topography on the wind parameters of periodic thermally-developed winds is discussed. • The regularity of the wind parameters changing periodically with time is identified. • The horizontal coherence of the fluctuating wind speed is studied. [ABSTRACT FROM AUTHOR]

The temporal and spatial distribution of wind fields in the deep-cut gorge bridge site is complex, and the impact of different incoming flows on the structure is also essentially different. Therefore, it is essential to comprehensively consider the correlation between wind direction, wind speed, and angle of attack. The joint probability models between average wind parameters are first established using the Pair-Copula decomposition based on the field-measured data. Then, the concept of the probability-segmentation-based first order inverse reliability method (PSB-IFORM) is proposed for calculating the environmental surface of the multi-peak joint distribution model. The results show that the mixed von Mises distribution is ideal to fit the wind direction with multi-peak characteristics. The trivariate joint probability model constructed in this paper ultimately represents the correlation of average wind parameters, and the most unfavorable combination of design wind parameters can be found on the environmental surface. Furthermore, the proposed PSB-IFORM can effectively avoid the defects of the inverse first-order reliability method (IFORM) and the conservative highest probability contour (HDC) method in solving the multi-peak joint probability distribution model. This study is of particular interest to researchers and engineers engaged in wind resistance of mountain structures. • The reasonable univariate distribution model of the mean wind parameters are found. • A binary and trivariate joint probability model with periodic bimodal characteristics are constructed. • The inverse first-order reliability method (IFORM) is improved and extended. • The environmental surfaces and contours of the mean wind parameters are solved. [ABSTRACT FROM AUTHOR]

Due to the local terrain and temperature, various types of intense wind, such as sudden intense winds, thermally developed winds, and thunderstorms, will occur in mountainous areas of different regions and periods of time. The identification and separation of intense wind events into different families are key topics in wind engineering to study the characteristics of intense winds in mountainous areas, which are essential to investigate the wind-excited response of structures. This research presents a systematic field measurement study on intense wind events in a deep-cut canyon situated in a mountainous area of southwestern China and identifies a series of sudden intense wind events whose wind speed, direction, ambient temperature, and other characteristics change rapidly. To distinguish and isolate such events, an automatic classification method was proposed, and 11 sudden intense wind events were captured. Additionally, it was also found that the sudden intense wind had relatively strong nonstationary characteristics. Finally, the average and fluctuating wind characteristics of sudden intense winds were investigated, and the time-variant characteristics were discussed in detail. These varying characteristics at high wind speeds, which will make the loads acting on bridges more complex, should be considered in the wind-resistant design of long-span bridges. • An automatic classification method is proposed for extracting sudden intense winds from long-term field measurement data in mountainous terrain. • A series of wind samples are found interesting with sudden changes in wind speed and temperature drops. • Sudden intense wind is found to have relatively strong nonstationary characteristics. • The regulation of fluctuating wind characteristics changing with time is discussed in detail. [ABSTRACT FROM AUTHOR]

The univariate design method may not match the wind resistance demands of bridges in mountainous areas. Therefore, it is crucial to comprehensively consider the joint effect of multiple wind parameters for determining wind-resistant design parameters of bridges. To address challenges such as short measurement periods and difficulties in expanding the extreme value model of wind parameters, a Bootstrap resampling strategy incorporating seasonal wind speed trends was developed, verified, and applied to long-term probabilistic modeling; thus, the uncertainty of the probability model of average wind parameters was investigated. Then, taking the environmental contour of wind speed and attack angle under varying wind directions as the basis, a technical framework for wind-resistant bridges based on multi-parameter joint design is proposed. Meanwhile, the main girder's longitudinal and lateral design wind speeds are derived under the joint influence of attack angle and yaw angle. The results show that the control wind direction of longitudinal and lateral design wind speed is different. The joint design considering multiple wind parameters effectively makes up the limitations of traditional methods. It provides valuable insights for wind-resistant design and lifecycle toughness evaluation of bridges in mountainous areas. • Developed a resampling method with seasonal wind trends for randomness quantification and long-term probabilistic modeling. • Established a mapping between turbulence parameters and wind speed for design value calculation and uncertainty evaluation. • Built a joint wind parameter design framework for long-span bridges based on field measurements. • Joint design wind speeds for a gorge long-span bridge were determined under large attack and deflection angles. [ABSTRACT FROM AUTHOR]

Long-span bridges are strongly sensitive to wind, and it is important to accurately assess the wind field of bridge sites. Thus, to strengthen the understanding of the wind field of deep-cut gorges and study the influence effect of the wind direction on the wind characteristic parameters, the wind data from an ultrasonic anemometer installed on a catwalk and bridge tower were used to perform statistical analysis. The results show that the wind characteristic parameters (including wind speed, wind attack angle, turbulence intensity and turbulence integral scale) vary greatly between directions. In addition, the wind speed, turbulence intensity and turbulence integral scale in all directions follow the log-normal distribution, whereas the attack angle follows the normal distribution. At the same time, the effects of incoming flow direction on the distribution of wind parameters differs between spatial points. In addition, without considering the influence of wind speed, the statistical distribution of the attack angle and turbulence intensity has adverse effects on the wind resistance of the structure. Therefore, the combined effect of wind speed and incoming flow direction should be considered in the wind resistance of structures. ∙ The distribution characteristics of wind parameters including wind speed, wind attack angle, turbulence intensity and turbulence integral scale in the deep-cut gorge bridge site are clarified, and the distribution differences of wind parameters under different incoming flows are revealed. ∙The relationship between wind speed and attack angle, turbulence intensity and turbulence integral scale is explored, and the influence of wind speed on the distribution characteristics of wind parameters is verified. ∙The influence of wind speed and wind direction on the wind resistant design of structures in the same deep-cut gorges is pointed out. [ABSTRACT FROM AUTHOR]

• The mixed intense wind climate was observed in a canyon by field measurement. • The classification framework and automatic program for mixed winds are set up. • Mean and fluctuating parameters of three intense winds are different significantly. • Time-frequency characteristics of turbulent kinetic energy for each wind compared. • The importance of mixed wind classification in mountainous terrain is emphasized. The wind in mountainous terrain is a mixed system, including large-scale synoptic wind and local-scale periodic thermally-driven wind. Placing all kinds of intense winds into one group may misestimate the mountain wind field's extreme wind speed and wind parameters. So, there is an urgent demand for classifying intense winds into homogenous groups. For this reason, a classification framework and extraction program for intense winds in mountain terrain according to their wind speed and temperature features is undertaken. A series of local-scale periodic thermally-driven winds, sudden intense winds, and large-scale cooling windstorms are identified and extracted from the long-term field measurements in a mountain area. Further, the mean and fluctuating characteristics of various intense winds are compared. The time–frequency changes of turbulent kinetic energy in several typical strong wind processes are studied through the evolutionary power spectrum. Remarkable differences are founded in wind parameters for intense winds with different scales. [ABSTRACT FROM AUTHOR]

To raise the wind speed prediction accuracy, Wavelet Transform (WT) is widely employed to disaggregate an original wind speed series into several sub series before forecasting. However, the highest frequency sub series usually has a great disturbance on the final prediction. In the study, for raising the forecasting accuracy, Singular Spectrum Analysis (SSA) is applied to make further processing on the highest frequency sub series, instead of making no modification on or getting rid of it. So a hybrid decomposition technology called Improved WT (IWT) is proposed. Meanwhile, a new hybrid model IWT-ENN combined with IWT and Elman Neural Network (ENN) is also designed. The procedure of IWT is systematically investigated. Experimental results show that: (1) the performance of the hybrid model IWT-ENN has a great improvement compared to that of others including the persistence method, ENN, Auto-Regressive (AR) model, Back Propagation Neural Network (BPNN) and Empirical Mode decomposition (EMD)-ENN; (2) compared to the two general strategies where the highest frequency sub series is without retreatment or eliminated, the new proposed hybrid model IWT-ENN has the best prediction performance. [ABSTRACT FROM AUTHOR]

Turbulence coherence in mountainous areas necessitates meticulous evaluation due to the complex terrain blocking. This study focuses on the turbulence coherence of the non-uniform wind field in a canyon via the anemometers positioned along a bridge span. Based on a proposed multi-point clustering, two categories of strong winds impacted by a nearby ridge are identified. The turbulence coherence of the two strong winds is then investigated with an extra focus on the phase spectrum. Several complex coherence functions are extended from commonly employed real forms, including the simplified Krenk's formula proposed. The fitting results of them all suggest that parameters such as the decay factor of the two strong winds show a negative linear correlation with separation but their relationship with wind speed is not significant. For the phase spectrum, in addition to skew winds, the contribution of horizontal wind shear is first emphasized in the two strong winds with piecewise fittings. This paper also discusses single-point coherence between the along-wind and vertical turbulence components. It is found to be unusually positive in sign due to the influence of the local topography and a formula with a constant term is suggested that substantially improves the fitting compared to Solari's formula. • The turbulence coherence with different separations is studied in a non-uniform wind field. • The strong winds are classified by multi-point clustering of the orthogonal components. • The contributions of horizontal wind shear and skew wind to the phase spectrum are emphasized. • The single-point coherence between different turbulence components is investigated. [ABSTRACT FROM AUTHOR]

Driven by local heat, the periodic thermally-developed wind often occurs in mountain terrain, and there is a strong correlation between wind speed and temperature. Other intense winds such as thunderstorms and sudden intense winds may also occur. Classifying mixed wind climates into homogeneous families helps accurately obtain the wind field characteristics and is essential to the structural wind-excited response in mountain terrain. For this reason, based on the long-term field measured data of the bridge site in a typical U-shaped canyon, a framework is set up to detect and extract periodic thermally-developed wind. Its statistical and time-varying wind characteristics are analyzed subsequently. Results show that the mean wind has a dominant direction along the canyon during the intense wind period, strongly correlated with the attack angle. The mean and fluctuating wind parameters will change obviously and periodically with wind speed every day. Due to the strong nonstationarity of these events, the power spectrum of pulsating components extracted from periodic thermally-developed intense wind events by the nonstationary model can be well described by Von Kármán power spectrum function. This study is of great significance to the structural durability and comfort for wind-sensitive structures in mountain terrain. • A series of periodic thermally-developed winds are identified from long-term measure data recorded in mountain terrain. • Strong correlations are found both between mean wind speed and temperature, wind direction and attack angle. • The periodic thermally-developed wind has such strong nonstationary characteristics that the nonstationary model is needed. • Mean wind parameters change with periodic variations daily. • The regulations of fluctuating wind parameters temporal and spatial distribution are discussed in detail. [ABSTRACT FROM AUTHOR]