Wide application of bridges makes transportation more convenient. However, there may exist a series of potential serious problems, for example, impact on the bridge structure, long-term overload, environmental factors, etc. [1]. Due to the above problems, many bridges around the world collapsed, such as the Ezhou huhua Interchange Ramp [2], Morandi Bridge in Italy [3] and Florida International University pedestrian bridge [4], etc. Those collapses of bridges caused serious disastrous disasters to people's lives and the social economy, which prompted people to hope for a system with a comprehensive and long-lasting health monitoring on the bridge. The structural health monitoring (SHM) system of bridges emerged to meet this demand [5].
In recent years, SHM has been widely used around the world for operational and building phase, including the Golden Gate Bridge [6] in the United States, Tamar Bridge [7] and Humber Bridge [8] in the United Kingdom, Yokohama Bay Bridge [9] etc. A typical SHM system usually consists of four parts: sensors, a data acquisition system, a data transmission system and a state evaluation system [10]. Researchers have done a lot of work on these aspects and achieved many excellent results. Maha Sliti et al. [11] pointed out that a fiber Bragg grating sensor can improve the structural safety through real-time vibration monitoring, which means that the Fiber-optic Bragg grating sensor has great potential for structural monitoring. M. Pieraccini et al. [12] developed Interferometric multiple-input multiple-output (MIMO) radar for remote monitoring of bridges, which has been successfully tested as geotechnical equipment during the real case of the monitoring of a historical bridge in the city of Florence, Italy. However, sensors with high-precision and high-performance are more expensive, which causes limitations for batch applications. Therefore, in the process of sensor selection, there may need a compromise between its accuracy and cost. In addition, long-term monitoring and density of information are also aspects to be considered.
Chen [13] used two Analog-to-digital converters to realize synchronous sampling of 12 channels. They have increased the integration of the acquisition cards by increasing the number of acquisition signal channels, which effectively reduced the number of data acquisition cards used in the system.
In the data transmission system, the traditional wired communication has reached maturity in terms of information transmission stability and information carrying capacity. The development of wireless communication technology has expanded the information communication method and provided new ideas for bridge monitoring information communication. Whelan et al. [14] introduced wireless sensing technology into bridge vibration testing. Nie et al. [15] proposed a bridge monitoring architecture through ZigBee. Al-Radaideh et al. [16] applied ZigBee transmission and GPRS transmission to bridge data transmission system at the same time. However, during the data transmission process of the wireless communication method, the signal is susceptible to electromagnetic interference, which means that the stability and security of this type of data transmission are poor. People have been pursuing high-precision, multichannel, and wireless communication methods in bridge monitoring systems. Progress in these aspects has contributed to a better monitoring of bridge status. But the acquisition board with high-performance has fewer input ports and higher price, which causes limitations for engineering batch applications. Monotonic transmission is difficult to ensure data stability and efficiency in long-term bridge monitoring.
From the perspective of bridge structure, bridge bearing is an important structural device for transferring loads between the upper structure and the lower structure of the bridge. The damage of the bridge bearing directly causes the deviation or imbalance of the upper and lower structures of the bridge, posing a threat to the overall safety of the bridge structure [17]. The bridge bearing monitoring could effectively and directly reflect the global mechanical status of bridge health. However, because of the concealment of the installation position of the bridge support, the manual detection method cannot accurately determine the damage degree. According to the characteristics of bridge health monitoring parameters, we develop a high-precision and real-time data acquisition system to measure the interface stress of the bridge support. High-precision data acquisition is obtained by selecting high-precision sensors, data acquisition boards with appropriate resolution and noise reduction algorithm optimization. Combined with cloud platform technology, a monitoring service system is built in the bridge site server and cloud server to facilitate real-time monitoring of dynamic changes of the bridge.
The rest of this paper is organized as follows. In Section 2 “Materials and Methods”, the overall design of the system is given. In Section 3 “System Hardware Design”, the sensor module, signal conditioning module, ADC module, FPGA module and communication module are introduced. In Section 4 “Software System Design”, the internal logic of FPGA, unscented Kalman filter and the construction of monitoring server are introduced. Experimental results of the proposed system are presented in Section 5 “Test and Result”. Conclusions and remarks on possible further work are given finally in Section 6 “Conclusion”.