1, Application in Civil and Hydraulic Engineering
Structural monitoring in civil engineering is the most active field of fiber grating sensor application. The measurement of mechanical parameters is very important for the maintenance and health monitoring of bridges, mines, tunnels, dams and buildings. By measuring the strain distribution of the above structure, the local load and health state of the structure can be predicted. Fiber Bragg grating sensors can be pasted on the surface of the structure or embedded in the structure in advance, and at the same time, the structure can be tested for health, impact, shape control and vibration reduction to monitor the defects of the structure. In addition, a plurality of fiber grating sensors can be connected in series to form a sensing network, and the structure can be detected in a quasi-distributed way, and the sensing signal can be remotely controlled by a computer.
2. Application in bridge safety monitoring
At present, the most widely used field of fiber grating sensor is bridge safety monitoring. Stay cables of cable-stayed bridges, main cables of suspension bridges, suspenders and tie bars of tied arch bridges are the key stress components of these bridge systems, as are prestressed anchorage systems of other civil engineering structures, such as anchor cables and anchor rods used for structural reinforcement. The stress magnitude and distribution changes of the above-mentioned stressed members directly reflect the health status of the structure, so it is of great significance to monitor the stress status of these members and analyze and evaluate their safety on this basis.
The Beddington Trail Bridge near Calgary is one of the earliest bridges to use fiber grating sensors for measurement (1993). 16 fiber grating sensor is attached to the steel bar and carbon fiber composite bar supported by prestressed concrete, which was previously considered impossible to monitor the bridge structure for a long time. There is a prestressed concrete bridge with a span of 72 m on the A 4 highway near Dresden, Germany. Meis-sner of Dresden University and others buried the Bragg grating in the concrete prism of the bridge to measure the basic linear response under the load, and compared it with the conventional strain gauge, which confirmed the feasibility of the application of the fiber grating sensor. During the construction of V aux box girder viaduct near Lausanne, Switzerland, the Swiss Stress Analysis Laboratory and the US Naval Research Laboratory used 32 fiber grating sensors to monitor the quasi-static strain of box girder during push and pull. 32 fiber gratings are distributed in different positions of the box girder, and the signals are demodulated by scanning berthing system.
In June, 2003, the health inspection project of Lupu Bridge hosted by Shi Jiajun, the Bridge Department of Tongji University, used the fiber grating sensor of Shanghai Zi Shan Optoelectronics to detect the stress, strain and temperature changes of the bridge under various working conditions.
Construction: The implementation of the whole testing project mainly includes three steps: sensor layout, data measurement and data analysis. Eight fiber grating strain sensors and four fiber grating temperature sensors are arranged at the selected end face of Lupu Bridge, of which eight fiber grating strain sensors are connected in series to 1 and four temperature sensors are connected in series to 1, and then transmitted to the bridge management office through optical fibers, thus realizing centralized management of the bridge. The period of data measurement is determined according to the owner's requirements, loaded on the bridge deck, and the dynamic strain test of the bridge is completed by using the fiber grating sensor network analyzer.
3. Application of concrete beam strain monitoring.
1989, Mendez of Brown University and others first proposed to embed optical fiber sensors in concrete buildings and structures, and described some basic ideas in this research field in practical application. Since then, universities and research institutions in the United States, Britain, Canada, Japan and other countries have invested a lot of energy to study the application of optical fiber sensors in intelligent concrete structures.
A very difficult problem encountered in pouring concrete structure is how to avoid damaging sensors and optical cables when pouring concrete. Fiber Bragg grating is usually written on ordinary single-mode communication fiber, which is fragile and easy to break. In order to adapt to the extensive characteristics of civil engineering construction, appropriate protective measures should be taken when it is used as a sensor to measure the strain of building structures.
A feasible scheme is: after arranging the optical fiber loop of the concrete strain sensor in the reinforcement cage, fix the concrete strain sensor in the reinforcement cage at a predetermined position with something like iron wire, and then wrap the middle section with gauze and fix it with adhesive tape. However, the bonded steel bar strain sensor is generally protected by an outer rubber layer.
In September 2003, the fiber grating sensor strain gauge independently developed by Shanghai Zi Shan Optoelectronic Technology Co., Ltd. was buried in concrete to measure the static strain of a landmark building in Zhongguancun, Beijing. The grating strain gauge independently developed by Shanghai Zi Shan Optoelectronic Technology Co., Ltd. has the advantages of high precision (generally 65,438+0 μ ε, small-scale strain measurement of 0.5με), high reliability, diverse installation methods and convenient use. It has been successfully applied to a landmark building in Zhongguancun, Beijing, laid on steel beams and buried in concrete to monitor the construction process of column steel beams.
4. Application of water level telemetry.
A high-precision optical water level sensor based on fiber grating technology is specially used to measure the water level of rivers, lakes and sewage systems. The accuracy of the sensor can reach 0.1%f s, and the fiber is installed inside the sensor, and FBG is formed due to the periodic change of the refractive index of the fiber core, which reflects the optical signal of a certain wavelength meeting the Bragg condition. When FBG is connected with elastic diaphragm or other equipment, the change of water level will stretch or compress FBG. And the reflection wavelength will change with the periodic change of refractive index. Then, the change of water level can be monitored according to the deviation of reflected wavelength.
5. Application in highway health detection.
The necessity of highway health monitoring;
Traffic is closely related to people, and it is also the main factor restricting the development of a city. It can be said that the quality of traffic can directly determine the development fate of a city. The state invests a lot of money in highway construction and maintenance every year, of which the maintenance cost accounts for a large part. Even so, there are still a large number of highways damaged every year, and the early damage of highways has become a major disease that affects the use of highways and induces traffic accidents. Damage is generally caused by overload, overspeed and natural reasons, which also has a great relationship with the quality of highway construction. Therefore, it is very necessary to carry out health examination in the process of highway construction and use. At present, highway construction is generally divided into three layers, namely subbase, ordinary layer and asphalt layer. In the process of construction, temperature and strain sensors can be buried to obtain the changes of temperature and strain in time and monitor the highway quality in real time. Understand the characteristics of building materials and the factors affecting construction quality in detail.