Jingyu Zhang

Aerodynamic characteristics of vehicles are directly related to their running safety, especially for the high-sided vehicles. In order to study the aerodynamic characteristics under multiple sheltering conditions, a complex large scale (1:20.4) truss model and three high-sided vehicles including articulated lorry, travelling bus and commercial van models with the same scale were built. The aerodynamic coefficients under various sheltering effects of wind barriers with different heights and porosities, bridge tower and the vehicle on the adjacent lane were measured. According to the results, wind barriers can effectively reduce wind speed behind them, thus decreasing the wind load acting on the vehicle, which causes the decrease of the aerodynamic response of all three vehicles. However, the influence at the leeward side is limited due to installation of central stabilizers. When the vehicle passes through the bridge tower, a sudden change occurs, the aerodynamic coefficients decrease and fluctuate in varying degrees, especially for the commercial van. When the vehicle moves in different lanes behind the bridge tower, the sheltering effect of the tower on the aerodynamic coefficient in Lane 1 is much greater than that in Lane 2. With regard to the interference between two vehicles on the adjacent lanes, the relative windward area between the test vehicle and the interference vehicle greatly affects the aerodynamics of the test vehicle.

Accurate and timely identification of modal parameters of long-span bridges is important for bridge health monitoring and wind tunnel tests. Wavelet analysis is one of the most advantageous methods for identification because of its good localization characteristics in both time and frequency domain. In recent years, the wavelet method has been applied more frequently in parameter identification of linear and nonlinear systems. In this article, based on wavelet ridges and wavelet skeleton, the improved modal parameter identification method was studied. To find the appropriate time-frequency resolution, an optimal wavelet basis design principle based on minimum Shannon entropy was proposed. Aiming at endpoint effect in wavelet transform, a prediction continuation method based on support vector machine (SVM) was proposed, which can effectively suppress the endpoint effect of the extended samples. In view of the fact that the ridges of metric matrices obtained by the traditional crazy climber algorithm cannot fully reflect the distribution of ridges of modulus value matrices of wavelet coefficients, an improved high-precision crazy climber algorithm was put forward to accurately identify the position of the ridge of wavelet coefficients. Finally, taking a long-span cable-stayed bridge and a long-span suspension bridge as the engineering background, improved continuous wavelet transform (CWT) was applied to modal parameter identification of bridge under ambient excitation. The modal parameters such as modal frequency, damping ratio, and mode shape were obtained. Compared with the calculation value of the numerical simulation of long-span cable-stayed bridge and wind tunnel test of long-span suspension bridge, the reliability of CWT for modal parameter identification of long-span bridges under ambient excitation was verified.

The wind environment and aerodynamic characteristics of vehicles are easily affected by the structural form of the railway. To investigate the aerodynamic effects of viaduct-cutting connection sections on vehicles, models of standard cutting, viaduct, and China Railway Highspeed (CRH2) trains at a scale of 1:20 were tested in wind tunnel tests. The wind speed profiles and vehicle aerodynamic coefficients were developed using a Cobra probe and balance, respectively. Additionally, the effects of wind barriers were applied. The test results indicate that the wind speed profile at the railway juncture is almost independent of the lateral positions at the same position. The aerodynamic influence of vehicles on different tracks (windward and leeward railway tracks) is different. Moreover, wind barriers can change both wind speed profiles and aerodynamic coefficients and significantly reduces wind speed and changes the aerodynamic coefficients to improve vehicle wind-resistant performance.

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.

To investigate the shielding effects of mountains in front of a bridge on the wind field at the bridge site in an area with complex topography, a numerical simulation model of the bridge site, which is located in a deep cut V-shaped gorge, was conducted by a computational fluid dynamics method. In this study, taking the shielding effects of mountains in front of the bridge into consideration, the mean velocity, wind attack angle, wind profile, and wind direction angle under different flow cases were calculated and compared. The spatial distribution characteristics of the wind field in an area with complex topography considering shielding effects are presented. The calculation results indicate that the characteristics of the wind field near the mountain at the bridge site are affected by the mountain and the direction of the incoming flow. The shielding effects of the mountain on the eastern side of the bridge are very different under different flow directions. The wind load distribution along the girder is severely uneven in some cases due to a local cyclone existing around the girder. The conclusions of this study provide a basis for improved wind resistance designs of bridges.

The sea-crossing railway bridge is exposed to a high risk of wind and wave, which threatens the safety of the bridge and railway. A wind–wave–vehicle–bridge dynamic analysis model for sea-crossing railway bridge under wind and wave loadings is developed by extending the previous wind–vehicle–bridge model. The developed wind–wave–vehicle–bridge model involves multipoint fluctuating wind field, irregular wave field, finite element model of the bridge, and mass–spring–damper model of the vehicle. The correlation between wind and wave is considered by an empirical curve derived based on field measurement. Static, buffeting, and self-excited wind forces on the bridge and vehicle are considered with coefficients obtained from wind tunnel tests. The wave forces on the bridge are calculated by Morison equation including stretching modification. The governing equations of the wind–wave–vehicle–bridge model are solved in time domain by Newmark-β method to compute the dynamic response of bridge and vehicle. The dynamic response of bridge and vehicle is compared and discussed in both wind–wave–vehicle–bridge and wind–vehicle–bridge model. The performance of bridge and vehicle are finally evaluated. Studies of dynamic response under correlated wind and wave are found to be imperative for assessment of structural and vehicle safety and driving comfort of sea-crossing railway bridge.

To improve the flutter stability of a long-span suspension bridge with double-decks, aerodynamic optimization on the upper and lower bridge decks is studied, and a series of countermeasures are considered, including slotted deck, wind fairings, porosity of guardrail, and horizontal and vertical stabilizers. Wind tunnel tests were performed to measure the critical flutter wind speed of the bridge and find effective aerodynamic countermeasures for improvement of the flutter stability. The results show that double-vertical stabilizers symmetrically installed at the two sides of the bottom of the lower deck with the distance of 9.32 or 11.55 m to the center efficiently improve the flutter performance of the original section at −3°, 0°, and 3° angles of attack simultaneously, while other common aerodynamic measures can hardly achieve this effect alone. The composite measure which consists of two central stabilizers installed on the top of the upper and lower decks, respectively, is promise and superior to the single measure. The combination of wind fairing and central stabilizer on the top of the lower deck is also an effective countermeasure. The results can provide the reference information for flutter optimization of the long-span steel truss girder suspension bridge with double-deck in the future.