As a new and sensitive sensing element, OFBG(Optical Fiber Bragg Grating) has been widely used in aerospace
engineering and civil engineering. The sensing mechanism and properties have been widely studied by lots of
researchers, but the sensing properties of OFBG under large negative strain are still destitute.
In this paper, with the aids of large shrinkage performance of PP(polypropylene) during its curing, we gained about -13000 με's strain changes by embeding bare OFBG inside the PP bar to study the sensing properties of OFBG in this
strain level. The results show that OFBG can remain its sensing properties well---- linearity, repeatability and the shape
of centre wavelength are both reasonably. And the strain sensitivity coefficient of PP-OFBG is about 0.85 pm/με, this is
very near with that of calculating results considering strain transmission between PP and OFBG. Which are all helpful and useful for further use of OFBG in other applications.
Stiffness of asphalt concrete is very low, so ordinary FRP or steel packaged sensors are not suitable for measuring its
strain accurately. In view of the problem, one innovative kind of optical fiber Bragg grating sensor packaged with
polypropylene, a thermoplastic resin, was proposed in this article. Firstly, a conveniently assembled and dissembled steel
die was designed and fabricated. Then, after characteristics study of polypropylene during heating and cooling
repeatedly, the reliable grouting technique was formed. After this, real-time monitor of the entire sensor packaging
process including die apartness was performed, and then, the sensor mechanics performance, the microscopic structure
and other properties were studied thoroughly. Results of SEM indicate that interface of optical fiber and polypropylene is
considerable tight. Measured strain during sensor making is reasonable. The FBG sensor was also embedded into a
concrete column to measure its strain during continuously 7 day-long early-age solidification and compressive strain.
Additionally, the FBG was also used to measure strain of asphalt concrete beam. Linearity and repeatability of the
sensors are quit well and measured strains are quite believable. So, we can say that due to deformation compatibility
between packaged material and FBG, FBG sensor and be measured material, especially low modulus of packaging
materials, the strain of asphalt pavement can be monitored reliably by the sensor.
Long lasting service performance has been one of the most important qualities in high way engineering. In this paper,
one type of strain sensor used for measuring and monitoring of asphalt pavement is presented and relevant numeric
analysis is introduced. Application of this kind of sensor in an express highway shows that the sensors based on Fiber
Bragg Grating technique and their embedding craft are applicable.
Construction monitor is an important way to ensure safety and economical efficiency at construction stage of civil
engineering, and monitor technique is one of the key elements to actualize the monitoring scheme. During construction
of the foundation of the Third Nanjing Yangtze Bridge, FBG techniques were adopted due to complex site environment
and high quality requirement of the engineering. The study group not only presented applicable embedding method of
FBG sensors, but also developed monitor software according to mechanical analysis of each object. The practice
demonstrates that the sensors worked well and had provided reliable data for decision-making in construction.
A new kind of FRP (Fiber Reinforced Polymer) packaged FBG temperature sensor is developed, and its installation
technique has also been studied. The experimental results show that this kind of sensor has good linearity, high accuracy.
and high sensitivity. During the construction of the Third Nanjing Yangtze Bridge they were applied to monitor the
temperature distribution of the mass concrete. The monitoring results of temperature distribution and its changes with
time, environmental temperature, setting retarder, and cooling water agree well with that from experience and qualitative
analysis. The practical application shows that the FRY-packaged FBG temperature sensors are proper to be used in
temperature monitoring in mass concrete structures.
It is a great challenge to prevent cracks occurring due to the temperature deviation of inside and exterior of large mass concrete structures during construction. 237 FRP (Fiber Reinforced Polymer)-packaged FBG (Fiber Bragg Grating) temperature and strain sensors have been used to monitor the temperature and strain course of mass concrete structures for construction control of Nanjing 3rd Yangtze Bridge. The practical investigation results show that the FRP-packaged FBG sensors are proper for construction control of mass concrete structures, which show great advantages rather than conventional sensors.
The feasibility and advantages of smart bridge cable based on FBGs are discussed. And the sensing properties of FBGs installed in the cables under dead load are tested. The experimental results and practical applications show that the smart bridge cable is proper to be used in bridge cables transfer, construction control and long-term health monitoring.