# Automated Real-Time Assessment of Stay-Cable Serviceability Using Smart Sensors
## 1 Introduction  
With increasing demand for long-span bridges, cable-stayed bridges have been widely applied to construction owing to their high structural stiffness and aesthetic appearance [1; 2]. Since the construction of the Stromsend bridge as the first modern cable-stayed bridge in Sweden (1955) [3], the maintenance of constructed bridges has received substantial attention to preserve their structural integrity and prolong their service life [4]. Among the various maintenance concerns of cable-stayed bridges, wind-rain-induced vibration has been recognized as one of the primary problems threatening their structural operability and serviceability since its first observation at the Meiko-West Bridge in Japan reported in 1986 [4; 5]. A stay-cable, which is one of the most significant load-carrying members of a cable-stayed bridge, is vulnerable to vibrations induced by external loads such as wind, rain, and traffic owing to its inherent low damping ratio with high flexibility [4; 6; 7; 8; 9]. Among other factors, excessive vibrations in a stay-cable cause long-term fatigue in it and impact the structural integrity of the entire bridge [4; 8; 10; 11]. Therefore, civil engineers are required to conduct maintenance measures on high priority to maintain the structural integrity of not only stay-cables but also cable-stayed bridges [4; 9; 10; 11; 12]. The structural integrity of any civil construction can be preserved by maintaining its serviceability and operability within acceptable levels with limited time and financial resources [4; 13]. Of these two parameters, serviceability tends to be a primary concern in terms of structural safety because users are likely to be sensitive to a serviceability issue far earlier than an operability issue [4; 14]. Note that serviceability determines the ability of a structure to be used, whereas operability is related to the ability of a system to continue functioning [4; 15]. As an effort to maintain the safe serviceability of a stay-cable, developed countries have assigned design codes that specify the allowable level of serviceability for bridge users [4]. In the United States, the vibration comfort level is assessed depending on the relationship between cable vibration and cable diameter, which is classified into three levels: \"not allowable\" when the amplitude of the cable vibration is twice the diameter of the stay-cable, \"recommended\" when the amplitude is close to the diameter, and \"preferred\" when the amplitude is approximately half the diameter [16]. The Korean government assigns the acceptable serviceability level of stay-cables based on the amplitude of vibration of the cable at mid-span, which is less than \(L/1600\) under an average oncoming wind speed of less than 20 m/s for 10 min, where \(L\) is the length of the subject stay-cable [4]. Both the Japanese and Chinese governments assign serviceability levels to cable-stayed bridges based on the deflection at mid-span of the bridge deck, which is less than \(L/2000\) and \(L/400\), respectively [12; 17]. Monitoring serviceability with respect to cable vibration should be emphasized as one of the critical maintenance efforts for cable-stayed bridges [4; 18; 19; 20]. An automated system that assesses the serviceability of stay-cables in real time is required to monitor their serviceability effectively. However, thus far, little work has gone into developing an automated real-time cable serviceability assessment system. Previous studies have focused on reducing vibration of the cable to improve the serviceability level or assessing the level of serviceability of stay-cables. For example, control schemes, such as active, semi-active and hybrid control, and dampers have been proposed and developed for vibration reduction of the cable [21; 22; 23; 24]. Furthermore, previous work by [PERSON] et al. (2019) developed an integrated cable vibration control system using smart sensors which embeds the semi-active control with magneto rheological (MR) damper [8].