## 1 Introduction  
In recent decades, wind disasters have become more and more violent across the world. Damages to property with attendant economic losses and casualties are frequently reported by the public media [1; 2]. Among the disasters, extreme wind events--e.g., typhoons/hurricanes, downbursts, tornadoes, etc.--have become the most severe cases that will cause destructive damages or significant performance deteriorations to engineering structures [2; 3]. With the worsening of global climatic environment, many places have been known as typical wind-prone areas. For example, every year the coastal area of East China will be attacked many times by the severe typhoons from the Pacific Ocean. However, in the wind-prone areas above, there are a great number of long-span bridges constructed or still under construction over rivers or even seas, which is catering to the developments of local transportation and economics [4]. With the rapid increase of the bridge span, the bridge will be a typical slender structure which is sensitive to the wind effects [5]. There are four main types of wind-induced vibrations occurring on bridges known as flutter, buffeting, galloping, and vortex-induced vibration. Among them, buffeting is a typical forced vibration induced by the turbulence existing inherently in natural wind. Different from the other three vibrations, buffeting is daily experienced by long-span bridges and becomes more prominent with the increase of the bridge span. Although the buffeting will not cause direct catastrophic failure to structures, it will result in instability of the vehicles travelling on the deck as well as discomfort of pedestrians, it will also severely shorten the fatigue life of structural components [6; 7; 8; 9; 10]. Many studies have been conducted on the buffeting performance of cable-supported bridges. For example, [PERSON] and [PERSON] investigated the buffeting responses of Tsing Ma Bridge under skew winds during Typhoon Sam [11]. [PERSON] et al. conducted a comparative study on the buffeting performance of Sutong Cable-Stayed Bridge based on design and measured spectrum [10]. In recent years, a typical bridge with a brand new type of structural form, which is called the triple-tower suspension bridge, has been put into engineering practices for long-span bridges, e.g., Taizhou Yangtze River Bridge and Ma'anshan Yangtze River Bridge in China. The triple-tower suspension bridge has not only two towers at the ends of two main spans, but also a dominant mid-tower between two main spans to alleviate the strain of main cables. Compared to the double-tower suspension bridge, structural characteristics of a triple-tower suspension bridge are strikingly different because of the existence of the middle tower and an additional main span [12; 13]. Most existing research focuses on the static analysis of long-span triple-tower suspension bridges [14; 15; 16]. Several studies also made efforts to the flutter stability [17; 18; 19]. However, few researches are concerned about the buffeting problem of the long-span triple-tower suspension bridge. With the increase of the bridge span, buffeting may perform an important role in the structural design of long-span triple-tower suspension bridges, especially for the ones located in the typhoon/hurricane-prone areas. In order to improve the travelling comfort and keep sufficient structural fatigue life, effective measures need to be adopted to mitigate the buffeting responses of long-span triple-tower suspension bridges during strong winds. There are a lot of dampers available in the vibration control of engineering structures--e.g., viscous damper, magnetorheological damper, tuned mass damper (TMD) [20; 21; 22; 23; 24]. Buffeting responses of long-span bridges are prominent in the main girder, which is a linear and flexible structure. Obviously, the viscous damper and magnetorheological damper are not easy to be applied in the vibration control since they are usually installed between two adjacent joints to alleviate the comparative motions.