The FBG sensor has globally been commercialized in various fields that is actively applied in Korea as well. Especially it is widely used as a structural monitoring sensor in civil engineering and construction structures due to its advantages including electrical stability, chemical stability and multiplexing. This report aims to introduce safety inspection of the FBG sensor in respect of radioactivity which has been applied to a silo structure for radioactive waste disposal as an example.
Fiber optic sensor system, which is not corrosible semi-permanent, no influence by electromagnetic waves, and able to
multiplex, can be expect to take an important part to assess the safety and residual estimate the life span of the highway
pavement structure.
In this research, as in situ monitoring of roughness of pavement, we propose the vibration monitoring method using fiber
optic sensors. We designed and produced prototype fiber optic vibration sensor packages. Laboratory impact tests with
the sensors were performed. The sensors showed very good responsibility to the impact and nice damping shape like
other ordinary accelerometers. Actual road tests with the prototype vibration sensor were also performed. The ambient
vibration by the vehicles was used for the experiment.
For monitoring of railway structures, optical fiber sensors are very convenient. The fiber sensors are very small and do
not disturb the structural properties. They also have several merits such as electro-magnetic immunity, long signal
transmission, good accuracy and multiplicity of one sensor line. Strain measurement technologies with fiber optic
sensors have been investigated as a part of smart structure. In this paper, we investigated the possibilities of fiber optic
sensor application to the monitoring of railway structures. We expect that the fiber optic sensors have much less noises
than electrical strain gauges because of electro-magnetic immunity while railways operate electric power of 22000 volts.
Fiber optic sensors showed good durability and long term stability for continuous monitoring of the railway structures as
well as good response to the structural behaviors during construction.
In this paper, a Fiber Bragg Grating (FBG) sensor system for smart structures is described. FBGs are well-suited for long term and extremely severe experiments, where traditional strain gauges fail. In the system, a reflect wave-length measurement method which employs a tunable light source to find out the center wave-length of FBG sensor is used. The real field test was performed to verify the behaviors of fiber Bragg grating (FBG) sensors attached to the containment structure in Uljin nuclear power plant as a part of structural integrity test which demonstrates that the structural response of the non-prototype primary containment structures within predicted limits plus tolerances when pressurized to 115% of containment design pressure, and that the containment does not sustain any structural damage. The system works very well and it is expected that it can be used for a real-time strain, temperature and vibration detector of smart structure.
In this paper, a Fiber Bragg Grating (FBG) sensor system for smart structures is described. FBGs are well-suited for long term and extremely severe experiments, where traditional strain gauges fail. In the system, a reflect wave-length measurement method which employs a tunable light source to find out the center wave-length of FBG sensor is used. The real field test was performed to verify the behaviors of fiber Bragg grating (FBG) sensors attached to the containment structure in Uljin nuclear power plant as a part of structural integrity test which demonstrates that the structural response of the non-prototype primary containment structures within predicted limits plus tolerances when pressurized to 115% of containment design pressure, and that the containment does not sustain any structural damage. The system works very well and it is expected that it can be used for a real-time strain, temperature and vibration detector of smart structure.
In this paper, a high speed fiber optic sensor weigh-in-motion (WIM) system is proposed. Bragg gratings which have several advantages such as good reproducibility and good multiplicity compare to other optical fiber sensors are used for the system. Fabry-Perot filter for the signal process, which cannot be used in the high speed measurement because of the limitation in fast operation of PZT, is excluded. A new signal processing system which employs bandwidth filter is proposed and bridge type new sensor package design is also proposed. The proposed fiber optic WIM system is tested in the laboratory and experimented with actual trucks. The new concept of calibration coefficient "k" is introduced and calculated by the experiments. The calculated calibration coefficients show good approximations to real axial weights regardless tire widths.
In order to extend the life time of building and civil infra-structure, nowadays, patch type fibrous composite retrofitting materials are widely used. Retrofitted concrete columns and beams gain the stiffness and strength, but they lose toughness and show brittle failure. Usually, the cracks of concrete structures are visible with naked eyes and the status of the structure in the life cycle is estimated with visible inspection. After retrofitting of the structure, crack visibility is blocked by retrofitted composite materials. Therefore, structural monitoring after retrofitting is indispensable and self diagnosis method with optical fiber sensor is very useful. In this paper, we try to detect peel out effect and find the strain difference between main structure and retrofitting patch material when they separate each other. In the experiment, two fiber optic Bragg grating sensors are applied to the main concrete structure and the patching material separately at the same position. The sensors show coincident behaviors at the initial loading, but different behaviors after a certain load.
Fiber Bragg grating (FBG) sensor systems are being widely used as temperature measurement and strain measurement systems for aerospace structures, civil structures, and high rise buildings. However, the systems are rather complicated because the wavelength change must be measured using several kinds of optical filters such as Fabry-Perot filters, edge filters, and bandwidth filters. In this paper, FBG sensor without filter system is proposed. The system consists of SLD (Super Luminescence Diode), diode driver, FBG sensors and the photo diode as a detector. Neither Fabry-Perot filter nor edge filter is applied. SLD has its own intensity slope according to various wavelengths. The slope is very linear at certain wave length range. In the beam experiments, the 1525 nm center wavelength FBG is employed as a sensor and the grating shows good linear responses to the dynamic loads. The data compare to those of electric strain gauges. The system also has a potential to be multiplexed by the pulse modulations in the time domain. If the FBGs have different wavelengths, they can be placed in the same fiber and if the FBGs have the same wavelength, they must be in the separate optical fiber and connected with couplers in order to be multiplexed.
Intrinsic Fabry-Perot optical fiber sensors were attached to a steel girder of the Sungsan Bridge which is one of the longest span bridges in Han River in Seoul, Korea. The tests were performed as parts of safety diagnosis of the bridge. We performed the visual inspection first, then we chose three spans for System Identification of the bridge. We applied numbers of strain gauges, acceleration sensors and a deflection gauge as well as optical fiber sensors. Static and dynamic loads were applied to the bridge with 30 ton weigh trucks. The optical fiber sensor system showed good responses to the static and dynamic loading with a resolution of approximately 0.12 (mu) strain. In conclusion,the optical fiber sensors can be used as elements of bridge monitoring system.
Civil structures play important roles in human being's life for convenience and practical purposes. But in the same manner, it needs proper maintenance because of the change of nature such as earthquake, typhoon, flood and the degradation of themselves with passing of time. Therefore, it has emphasized necessity of health monitoring system that always measures degree of deterioration of civil structure and predicts the life span of the structure and informs its repair time. Besides the existing strain gauge, potential candidates of the sensing elements of the system are optical fiber sensors because of no disturbance from electromagnetic waves, good durability, quick response. In this experiment, embedded intrinsic Fabry-Peort optical fiber sensors were employed.
Intrinsic Fabry-Perot optical fiber sensors were embedded to the tensile side of the 20 cm by 20 cm by 150 cm cement concrete structures. The sensors were attached to the reinforcing steels and then, the cement concretes were applied. It took 30 days for curing the specimens. After that, the specimens were tested with 4-point bending method by a universal testing machine. Strains were measured and recorded by the strain gauges embedded near optical fiber sensors. Output data of fiber sensor showed good linearity to the strain data from the strain gauges up to 2000 microstrain. The optical fiber sensors showed good response after yielding of the structure while embedded metal film strain gauges did not show any response. We also investigated the behavior of the optical fiber sensor when the specimens were broken down. In conclusion, the optical fiber sensors can be used as elements of health monitoring systems for cement concrete infra-structures.
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