###### Abstract  
Twin-box girders are a good option for long-span cable-bearing bridges due to their excellent stability. Nonetheless, the girder's slots may generate vortex-induced vibrations (VIVs). Fortunately, appropriate aerodynamic measures can effectively suppress the VIVs in twin-box girders while reducing costs. To examine the effects of vortex isolation plates with varying aperture diameters and opening ratios on the VIVs, a segment model wind tunnel test was conducted. The results demonstrated that a reduction in the opening ratio improved the performance under heaving VIVs, but there was no discernible trend under torsional vibrations. It was also discovered that the opening size significantly influences the length of the lock-in region of torsional vibrations. Furthermore, heaving VIVs have a substantial correlation with both of the girder's boxes, while torsional vibrations are mostly connected with the downstream section. VIV; vortex isolation plate; wind pressure; twin-box girder; wind tunnel test 2  
slot spacing between the upper and lower girders can affect the interactions, subsequently affecting the aerodynamic force. [PERSON] et al. (2018) conducted a study on slot spacing and found that unslotted sections have a better VIV performance compared to slotted sections. [PERSON] et al. (2018) used numerical simulations to show that a twin-box girder with a large angle of attack (AOA) would have large-scale vortex shedding in the downstream section. [PERSON] et al. (2018) found that the presence of a central slot enhances the overall vortex-induced force in an analysis of the aerodynamic evolution process. Additionally, by analyzing the field-measured data gathered in a wind tunnel test at Xihoumen Bridge, it was found that the vortex shedding in the slot and of the downstream box girder surface is closely related to VIVs ([PERSON] et al., 2019; [PERSON] et al., 2020). According to current research, a close correlation exists between the VIVs in twin-box girders and the central slot. Based on this, [PERSON] et al. (2018) conducted a wind tunnel test using a central stabilizing plate to study the performance of twin-box girders under VIVs. The results of this study indicated that the size and placement of the central stabilizing plate had a significant impact on vibration suppression. The research conducted by [PERSON] et al. (2018) focused on a wide twin-box girder, identifying a vortex isolation net as an effective means of mitigating VIVs. Additionally, [PERSON] et al. (2020) utilized delayed detached eddy simulations to study the function of the central grid, concluding that the central grid was beneficial for suppressing VIVs in twin-box girders. Furthermore, some scholars have implemented aerodynamic measures at various positions in twin-box girders to try to mitigate the effects of VIVs, which have proven to be effective. For example, an investigation of the Hong Kong-Zhuhai-Macao river/sea direct ship channel bridge revealed that a guide plate set on the web can effectively suppress VIVs ([PERSON] et al., 2020). Similarly, [PERSON] et al. (2020) examined Jiashao Bridge and found that a windshield plate in the bridge deck and a guide plate set at the bottom of the section can also suppress VIVs in twin-box girders. [PERSON] et al. (2020) identified that heaving VIVs can be suppressed by introducing a cover plate to form a streamlined wind fairing with the sidewalk. In conclusion, extensive research conducted on VIVs in twin-box girders has yielded significant results and valuable recommendations for engineers. However, the VIV and vibration-suppression mechanisms remain unclear. Therefore, a more comprehensive investigation into the influence of aerodynamics on twin-box girders is necessary. In this paper, a deep analysis focusing on twin-box girders is performed, and the impact of a vortex isolation plate on the performance under VIVs at different AOAs is examined.