# Automated Real-Time Assessment of Stay-Cable Serviceability Using Smart Sensors
## 5 Conclusions and Discussion  
In this study, an automated real-time serviceability assessment system using wireless smart sensors was developed to monitor the serviceability of the stay-cable in a cable-stayed bridge, which operates at low cost and consumes low power. The developed system consists of a gateway node and leaf node connected to each other through Bluetooth communication. The gateway node commands the leaf node to assess the serviceability and monitor the serviceability level, and the leaf node assesses the serviceability of the stay-cable. The gateway node was designed using a Bluetooth device to check the serviceability condition of the stay-cable. Smart sensors with low cost and low power consumption were used to develop the leaf node, which is based on the Raspberry Pi 3 Model B+ single-board computer and MEMS accelerometer with ADC sensor. The system features embedded on-board processing to measure the acceleration, estimate the displacement from the measured response, and diagnose serviceability failure based on the US design code [16]. Note that the measured acceleration of the stay-cable is converted into dynamic displacement based on a previous study [26]. A series of experiments were conducted using a laboratory-scale cable to verify the developed system, and the results indicate that the system can monitor the serviceability of the stay-cable using a single type of measurement data with the Raspberry Pi-based single-board computer. In addition, the leaf node installed on the cable can be remotely commanded by the gateway node, in particular, using the Bluetooth device, which aids inspectors in monitoring the serviceability level of the stay-cable conveniently. Because the Bluetooth is appropriate for short distance communication, other wireless communication modules such as LoRa, WiFi, and Zigbee can be applied to implement wireless communication between the gateway and leaf nodes in the future work.  
As a new pioneering study implementing wireless smart sensors for the maintenance of stay-cables, the developed system can be applied not only for monitoring serviceability but also for other maintenance purposes. For example, a damper system such as a passive, active, and magneto-rheological damper has been widely applied to enhance the damping performance of the stay-cable as a means to reduce the cable vibration [4; 8]. The developed system can be used to evaluate the performance of the damper in terms of reducing vibration by monitoring the vibration of the cable  
Figure 6: Wireless communication results of serviceability assessment for serviceability threshold of 1 mm.  
before and after the damper installation. When the serviceability of the stay-cable fails continuously despite the installation of the damper, the developed system allows inspectors to adjust the damper performance to reduce the vibration enough to meet the serviceability criterion. The developed system can be extended to monitor the tension force in the cable by embedding an automated tension estimation algorithm using acceleration data obtained using the vibration-based indirect method. In conclusion, the results of this study are expected to expand present knowledge on the application of smart sensors to monitor the structural health of the stay-cable.  
Conceptualization, [PERSON] and [PERSON]-[PERSON]; formal analysis, [PERSON]; methodology, [PERSON] and [PERSON]-[PERSON]; supervision, [PERSON] and [PERSON]; validation, [PERSON]-[PERSON]; writing--Original draft, [PERSON]; writing--Review and editing, [PERSON]-J.L., [PERSON], and [PERSON]-H.S.  
This research was supported by a grant (19 SCIP-B128569-03) from Smart Civil Infrastructure Research Program funded by Ministry of Land, Infrastructure and Transport of Korean government.  
The authors declare no conflict of interest.