# Wind Load Characteristics of Wind Barriers Induced by High-Speed Trains Based on Field Measurements
## 1 Introduction  
With the rapid development of the high-speed railways, the safety and comfort of high-speed trains under strong winds has drawn extensive attention worldwide [1; 2; 3; 4; 5]. [PERSON] et al. [6] proposed three strategies to improve the running safety of a train under strong winds; namely, optimization of the aerodynamic shape, operation management, and installation of wind barriers. However, optimization of the aerodynamic shape is impractical for existing trains. Operation management will bring about, for instance, speed limitations and temporary out of service times, which will lead to train delays and inefficiency in transportation. Moreover, this goes against the superiority of high-speed trains, which promote all-weather, fast, and on-time operations. In light of this, wind barriers can create a relatively low-wind environment for high-speed trains. The wind barrier is, therefore, an effective measure to improve the safety of high-speed trains in existing railway lines. In recent years, significantachievements on wind barriers have been obtained [7; 8; 9; 10; 11; 12; 13; 14; 15]. The relationships of wind-resistant effects, ventilation rates, and other parameters have been established preliminarily [16]. Wind barriers have been successfully implemented in some practical railway engineering, especially in China [17]. As a consequence of the limited width of the railway line, the wind barrier is usually close to the track to guarantee its wind-resistant effects. Supported girder bridges with spans of 32 m have been widely used in China's high-speed railways. The distance from the wind barrier to the nearest wall of the train is only about 1.75 m. Based on the height of the wind barrier, usually around 3.0 m, the reliability of the wind barrier itself could be a threat to traffic safety because of the strong impact generated by train-induced wind on the wind barrier. Some field test results showed that the pressure amplitude of the train-induced wind load acting on the wind barrier can be more than 1000 Pa, which far outweighs other loads [18]. Barrier cracks, fatigue failures, and other damage caused by the wind induced by high-speed trains have been observed [19]. In 2003, Germany expended approximately 30 million euros to reconstruct and repair the barriers along the Cologne-Frankfurt high-speed line due to fatigue failure induced by high-speed train passes [16]. Fluctuating forces caused by train-induced wind is one of the most significant control factors in the dynamic design of the accessory components of the railway, especially for high-speed railway lines. It has been realized that the effect of train-induced wind is proportional to the square of the train's running speed. The running speed of China's high-speed trains significantly exceed the world's average running speed for high-speed trains (240 km/h) and the maximum running speed (320 km/h). Therefore, significant investigations of the wind loads generated by high-speed trains on the wind barriers in China are highly necessary in order to build a solid background about the design of wind barriers. Train-induced wind is a complex, three-dimensional, and unsteady flow. However, accurate simulations of such three-dimensional unsteady flows cannot be achieved through existing wind tunnel tests as general wind tunnels can only simulate pulsating airflow in one direction. In order to produce a multiphase airflow, a multi-fan active wind tunnel is required. However, such wind tunnels are rare worldwide. Moreover, the maximum wind speed of such multi-fan active wind tunnels is far less than the speed of train-induced winds. Therefore, numerical simulations using computational fluid dynamics (CFD) software packages have become an appropriate and popular method to study the effects of train-induced wind loads on wind barriers. A moving train can be realized through a moving grid in the numerical simulations and the train-induced winds can be simulated [20; 21; 22].