# Evaluation of Ride Comfort under Vortex-Induced Vibration of Long-Span Bridge
## 1 Introduction  
To reduce transportation costs, minimize spatial-temporal distances between regions, and align with the trends of regional integration and economic globalization, countries are actively constructing and enhancing transportation networks through infrastructure development. As the integral components of infrastructures, including high-speed railways and sea-crossing channels, long-span bridges have been widely constructed and applied all over the world, creating new span records [1]. Wind-induced vibrations, such as flutter, galloping, buffeting, and vortex-induced vibration, present significant challenges to the stability of long-span bridges. Among these vibration types, vortex-induced vibration is the most prevalent, occurring in numerous bridges both domestically and internationally [2; 3; 4; 5; 6]. Vortex-excited vibration is a wind-induced, self-excited vibration that typically manifests at low wind speeds on long-span bridges, and it is theoretically inevitable. Contrary to divergent vibrations like flutter and galloping, VIV rarely causes dynamic instability or catastrophic bridge damage. However, its relatively high amplitude, coupled with frequent occurrences, can inevitably reduce the structural strength and fatigue resistance of bridges [7; 8; 9], impacting visual safety and ride comfort. In 2020, significant vortex vibrations with amplitudes ranging from 0.1 m to 0.3 m were observed on the Humen suspension bridge in China [10]. Other examples of VIV occurrences on real bridges include the Xiioumen Bridge [6] and Yingwuzhou Yangtze River Bridge [11] in China, as well as the Yi Sun-sin Bridge in Korea [12]. Investigations revealed that, despite the short duration of these conditions, several drivers experienced different levels of short-term physical discomfort [13]. The occurrence of vortex vibrations on the Humen Bridge led to panic among the on-site personnel and drivers, posing a significant traffic safety hazard. As a result, the bridge had to be closed for up to ten days, resulting in significant economic losses and public outcry [10]. Despite its limited amplitude, VIV can contribute to vehicle vibrations, causing short-term discomfort during extended driving. Concurrently, the literature shows that long-term high-intensity whole-body vibrations increase health risks, particularly to the lumbar spine and related nervous systems, as outlined in ISO 2631 [14]. Vehicle ride comfort remains a global research focus. Most studies concentrate on drivers' and passengers' comfort with respect to vibrations in everyday wind conditions, while also accounting for road irregularities and crosswinds. [PERSON] et al. [15] proposed a comprehensive evaluation method for vehicle ride comfort and driving safety on a slender coastal bridge under the influence of vehicle, wind, and wave loads, which evaluates ride comfort using the Overall Vibration Total Value (OVTV) index recommended by the ISO 2631-1 standard [14] and analyze driving safety based on roll safety criteria (RSC) and sideslip safety criteria (SSC). [PERSON] et al. [16] assessed the ride comfort of vehicles travelling on a slender arch bridge, which is made of ultra-high performance fiber-reinforced concrete (UHPFRC) and under turbulent crosswinds; the results showed that the bridge's vibration response is significantly affected by crosswinds in terms of peak acceleration and frequency distribution. [PERSON] et al. [17] investigated the comfort of drivers and passengers considering the road surface roughness and crosswind; the results showed that both road surface roughness and wind load have a significant impact on the comfort of drivers and passengers. [PERSON] et al. [18] numerically evaluated the ride comfort of three representative vehicles and assessed the impact of dynamic interaction between the bridge and the vehicle on ride comfort, considering typical traffic flow and wind excitation on a prototype of a long-span bridge. [PERSON] et al.