Prestress loss is critical to impact the safety of prestressed reinforced concrete (RC) structures. Unfortunately, up to now,
there are no qualified techniques to handle this issue. This paper proposes a life-cycle concept to monitor the full-scale
prestress loss of RC beams utilizing optical fiber distributed sensors. And the optical fiber distributed sensors-based
smart steel strands and load cell were configured. A prestressed RC beam with embedded smart steel strands was built to
illustrate the above methodology. The prestress loss data obtained from the smart steel strand and load cell agrees well,
and also matches that from the theoretical code.
It is still a big challenge to set up a durable and stable long-term liquid pressure monitoring system at many points for
long pipeline under harsh environment. In this paper, according to the need from customers, a practical high-reliable
liquid pressure sensor based on dual optical fiber Bragg grating (FBGs) has been studied and developed. The FBG-based
liquid sensor structure has been brought forward and optimized, and its sensing principle has also been given in details.
Besides, the novel sensor has been tested by serious experiments. The research results show that the FBG-based liquid
pressure sensor has good linearity, repetition and immunity of temperature changes, and the theoretical sensitivity agrees
well with that from the experimental results. Such kind of FBG-based liquid pressure sensor can be applied in practical
Optical fiber Bragg grating (FBG) has been accepted widely throughout the civil infrastructures, especially for bridges.
In this paper, a new case study, FBG-based intelligent monitoring system of the Tianjin Yonghe Bridge is introduced.
For this case, techniques of FBG sensors installation have been tested and 40 FBG strain sensors, 10 FBG temperature
sensors and 96 FRP-OFBG based smart cable sensors have been successfully installed on Yonghe Bridge. The concrete
strain change and cables load gradients have been monitored during the bridge static test using those FBG sensors. And
besides, after the bridge was completed, the strain course under traffic load and temperature changes were monitored
with these sensors. The monitoring results show that traffic fluxes and possible fatigue damages can be conveniently
analyzed, which can be applied for structural health diagnosis. The monitoring system has stood the ordeal for more than
2 years, which shows that the FBG can meet the demands of long-term monitoring of the bridge.
Optical Fiber Bragg Grating (OFBG) is now widely accepted as smart sensor due to its advantages of electric-magnetic resistance, small size, distributed sensing, durability, and so on. However, to our great regret, the bare FBG can only stand 3000~5000με, which can not satisfy the need of practical strain monitoring of infrastructures, especially for the damage detection, such as crack and large strain. In this paper, new technique of sensitivity-decreasing of FBG strain sensor has been brought forward and a new kind of FBG-based crack sensor is also developed. The novel FBG-based crack sensor (also named large FBG strain sensor) can detect 100,000με at maximum, just like 20mm crack at the calibration length of 20 centimeter, and the accuracy can reach 0.01 mm. The new kind of crack sensor is proper for high accuracy crack detection for long-term structural health monitoring of infrastructures.
Ice pressure is one of the most important loads in high-latitude area. It is challengeable to build a durable and stable real-time structural health monitoring system for ice-pressure under such aggressive environment as windiness, coldness, and even vibrating, which can not be met by strain gauge based sensors, whereas FBG fits it well due to its great advantage of corrosion resistance, absolute measurement, high accuracy, electro-magnetic resistance, quasi-distribution sensing, absolute measurement and so on. In this paper, a novel FBG based ice-pressure sensor has been developed. Firstly, in consideration of the monitoring of ice-pressure of offshore platform, a novel ice pressure sensor structure has been designed and it sensing principle is given in details, which theoretically shows the properties of temperature self-compensation and independence of the load position. And secondly, the properties of FBG-based ice-pressure sensor have been tested by experiments. Finally, theoretical sensitivity has been compared with that from experiments. The research results show that the FBG-based ice-pressure sensor has good linearity, repetition, immunity of temperature changes and loading position. Such kind of FBG-based ice-pressure sensor can be used to monitor ice load of offshore platform conveniently.