1. Characteristics of Fiber Grating Technology

Fiber Bragg grating is an optical sensor that forms a periodic refractive index modulation structure within the fiber core through ultraviolet laser, and it has several outstanding advantages. Firstly, its measurement accuracy is extremely high, with a strain resolution of up to 1 microstrain and a temperature measurement accuracy of ±0.1℃. Secondly, it has extremely strong anti-electromagnetic interference ability and is particularly suitable for use in strong electromagnetic environments such as substations and subways. Furthermore, it is made of quartz glass material, which has excellent corrosion resistance and a service life of over 20 years. In addition, a single optical fiber can be connected in series with multiple gratings to achieve distributed measurement, which greatly improves the monitoring efficiency. These characteristics make it an ideal choice for long-term monitoring in civil engineering.

2. Main Application Scenarios

In bridge engineering, fiber Bragg gratings are widely used in strain monitoring of key parts such as main beams, piers and abutments, and cables, which can monitor the stress changes caused by vehicle loads and wind loads in real time. Meanwhile, by dynamically monitoring the vibration frequency of the bridge, the degradation of the structural stiffness can be effectively evaluated. Many large Bridges, such as the Tsing Ma Bridge in Hong Kong and the Sutong Yangtze River Bridge, have adopted this technology for long-term health monitoring.

Tunnel and underground engineering monitoring is another important application field. By pre-embedding fiber Bragg grating sensors in the tunnel lining, the strain changes caused by the surrounding rock pressure can be accurately monitored, and the possible collapse risks can be warned in a timely manner. If sensor networks are arranged in soft soil foundations or subway tunnels, the uneven settlement can be monitored in real time. Engineering practices such as Shenzhen Metro have proved the reliability of this technology.

In terms of building structure monitoring, fiber Bragg gratings can be used not only for wind vibration and seismic response monitoring of high-rise buildings, but also for stress concentration analysis of large-span spatial structures. The monitoring of steel roofs at Beijing Daxing International Airport and the wind vibration monitoring of super high-rise buildings at Shanghai Tower are both typical application cases.

In slope and geological disaster monitoring, implanting fiber Bragg grating sensors into anchor rods or soil can accurately capture the strain changes in the slip zone, providing key data for landslide early warning. Both the slope monitoring projects in the Three Gorges Reservoir Area and those on expressways have achieved good results.

For concrete structures, fiber Bragg gratings can not only monitor the hydration heat temperature field during the pouring of large-volume concrete to prevent the occurrence of temperature cracks, but also indirectly detect the corrosion and expansion of steel bars by combining with rust-sensitive materials. They play an important role in projects such as hydropower station DAMS and nuclear power plant containment vessels.