## 1 Introduction  
More and more long-span bridges choose double-deck truss girders because of their high rigidity, low cost, and quick construction [1, 2]. Truss girders are composed of many discrete parts, and expansive double-layer bridge decks are prone to multiple eddy current regions, and various instances of multi-frequency vortex shedding occur, which complicates the VIV of truss girders. In addition, steel truss girders have partly changed members along the axis, making VIV difficult to evaluate [3, 4, 5]. VIV is one of the typical wind-induced vibrations of bridges. It is self-excited and forced, so it is easy to cause fatigue damage to the structure, and it significantly impacts driving comfort and safety [6, 7, 8, 9, 10]. In order to ensure the safety of structures and avoid disasters and financial losses caused by wind-induced vibration, structural health monitoring is a necessary procedure for long-span bridge structures [11, 12]. Xihoumen Bridge [13], Humen Bridge [14], Rio-Niteroi Bridge [15], and Second Severn Bridge [16], have experienced obvious VIV. Therefore, research on VIV suppression measures of long-span bridges is vital [17]. Currently, the measures commonly used to suppress VIV mainly include structural, mechanical, and pneumatic measures [18, 19, 20, 21, 22]. Aerodynamic measures improve the aerodynamic stability of structures by changing the shape of bridge structures [23]. VIV is very sensitive to aerodynamic shape, and various aerodynamic measures may suppress the larger amplitude to meet the engineering requirements. Standard aerodynamic measuresinclude setting fairing, stability plates, and deflector plates, changing the shape of the railings, changing the ventilation rate of the railings, adjusting the height of the sidewalk base, and changing the position of the maintenance lane. Aerodynamic measures involving deflector plates have the characteristics of simple structure, convenient setting, and remarkable vibration suppression effect [24; 25; 26; 27]. This paper mainly studies the influence of aerodynamic measures involving deflector plates on the VIV of double-deck truss girders. Scholars conducted a detailed study of deflector geometry, dimensions, and mounting positions, focusing on the effect of changing geometry, dimensions, and mounting positions on VIV. [PERSON] et al. [28] studied the effect of an inverted L-shaped deflector on the VIV of a main girder section by taking the side-box \(\Pi\)-shaped girder section as the test object and finally arrived at the practical application range of inverted L-shaped deflector plate size. [PERSON] et al. [29] studied the VIV of a main girder and the effect of pneumatic measures on vibration suppression by using a \(\Pi\)-shaped cable-stayed bridge as the engineering background and gave the amplitude effect curves of the bridge structure by using the variable control method with different size combinations under three aspect ratios. The results showed that the larger the horizontal and vertical dimensions of the inverted L-shaped deflector were, the better the VIV suppression effect of the bridge. [PERSON] et al. [30] explored the mechanism of VIV of a double-deck truss girder through a wind tunnel test and numerical simulation. The results showed that because the double-deck truss girder was composed of multiple members, vortices with different main frequencies were formed in the wake region. The vertical VIV of the bridge may be caused by the eddy current behind or above the bridge. [PERSON] et al. [31] explored the influence of aerodynamic measures on the VIV of a double-deck truss girder through wind tunnel tests and numerical simulations. The results showed that the upper chord fairing and the lower chord inverted L-shaped deflector plate played a vital role in suppressing VIV. [PERSON], [PERSON] et al. [32] proposed a method for predicting wind speed to improve VIV for various natural frequencies of a road-rail bridge with truss girders.