The importance of real-time detection of cable force during stretching construction can hardly be overstated, especially in long-span space cable system. In this paper, a novel approach to monitor the cable structure health using fiber Bragg grating (FBG) sensors was elaborated and applied in monitoring the tensioning process of suspend-cable dome of Dalian Gymnasium under construction. The encapsulated FBG strain sensors were adhered to the anchor to detect the cable force. Calibration tests conducted prior to leaving factory in order to get the cable force sensitivity coefficient were also presented. The monitoring results of stage stretching construction prove that this cable force monitoring method based on FBG sensors has advantages of easy installation, non-destruction to structure and high precision, showing promising potential in cable structure health monitoring.
An extensive model test program had been carried out to investigate the issues of ice loading on bridge pier model. This
paper investigated design principle of three kinds of FBG sensor modules, including FBG-based displacement sensor
module, FBG-based strain sensor module and FBG-based force sensor module. A series of calibration tests of all FBG
sensors had been made to detect the sensitivity of FBG sensor modules previously. There were 12 FBG-based sensors
applied to monitor the failure progress and to predict the cracking inside the bridge pier model. The results of the ice
loading tests proved that the FBG-based sensor had many advantages, characterized by its small size, high precision,
easier installation, water resistance and cold resistance, demonstrating promising potentials in cracking and failure
monitoring of bridge pier model.
Fiber Bragg grating (FBG) sensors demonstrate great potentials for structural health monitoring of civil structures to
ensure their structural integrity, durability and reliability. The advantages of applying fiber optic sensors to a tall building
include their immunity of electromagnetic interference and multiplexing ability to transfer optical signals over a long
distance. In the work, FBG sensors, including strain and temperature sensors, are applied to the construction monitoring
of an 18-floor tall building starting from its construction date. The main purposes of the project are: 1) monitoring the
temperature evolution history within the concrete during the pouring process; 2) measuring the variations of the main
column strains on the underground floor while upper 18 floors were subsequently added on; and 3) monitoring the
relative displacements between two foundation blocks. The FBG sensors have been installed and interrogated
continuously for more than five months. Monitoring results of temperature and strains during the period are presented in
the paper. Furthermore, the lag behavior between the concrete temperature and its surrounding air temperature is
investigated.
Accurate measurement of strain variation and effective prediction of failure within models has been a major objective for
strain sensors in dam model tests. In this paper, a FBG strain sensor with enhanced strain sensitivity and packaged by
two gripper tubes is presented and applied in the seismic tests of a small scale dam model. This paper discusses the
principle of enhanced sensitivity of the FBG strain sensor. Calibration experiments were conducted to evaluate the
sensor's strain transferring characteristics on plates of different material. This paper also investigates the applicability of
the FBG strain sensors in seismic tests of a dam model by conducting a comparison between the test measurements of
FBG sensors and analytical predictions, monitoring the failure progress and predicting the cracking inside the dam
model. Results of the dam model tests prove that this FBG strain sensor has the advantages of small size, high precision
and embedability, demonstrate promising potential in cracking and failure monitoring and in identification of the dam
model.
When a fiber Bragg grating (FBG) sensor is embedded in a structure to sense its strain, a portion of strain is absorbed by the protective interlayer of the fiber optical sensor. If an angle exists between the FBG sensor axis and external principal stress direction of the host material, the strain transfer from the host material to the sensor will be much different than that of the external stress parallel to the sensor axis. A suitable strain transfer model is developed for evaluating the interaction between the surrounding matrix and a length of optical fiber under nonaxial stress. A number of realistic assumptions are introduced to simplify the process of the mathematics rigor. Strain transfer rate is introduced to describe the level of strain loss within the protective interlayer and the amount transferred to the optical fiber core. Theoretical results show that the angle of the optical fiber sensor plays an important role in strain transferring from the surrounding materials to the optical fiber core. The theoretical findings are verified through a series of experiments with FBG sensors. The evaluation error of average strain transfer rate is discussed because of sensor-located angle deviation.
Biomechanical studies often involve measurements of the strains developed in tendons or ligaments in posture or
locomotion. Fiber optic sensors present an attractive option for measurement of strains in tendons and ligaments due to
their low cost, ease of implementation, and increased accuracy compared to other implantable transducers. A new
displacement sensor based on fiber Bragg grating and shape memory alloy technology is proposed for the monitoring of
tendon and ligament strains in different postures and in locomotion. After sensor calibration in the laboratory, a
comparison test between the fiber sensors and traditional camera displacement sensors was carried out to evaluate the
performance of the fiber sensor during application of tension to the Achilles tendon. Additional experiments were
performed in cadaver knees to assess the suitability of these fiber sensors for measuring ligament deformation in a
variety of simulated postures. The results demonstrate that the proposed fiber Bragg grating sensor is a high-accuracy,
easily implantable, and minimally invasive method of measuring tendon and ligament displacement.
Fiber Bragg grating (FBG) sensors show superior potential for structural health monitoring of civil structures to ensure their structural integrity, durability, and reliability. In this work, FBG sensors, including strain and temperature sensors, are applied for health monitoring of the oil production offshore platform number CB271, which is located in the Bohai Sea, East China. The procedure of FBG sensor installation during platform construction, as well as model validation in a laboratory under a variety of loading conditions on a seismic simulation shaking table, is also presented. In the tests, FBG strain sensors are placed as a strain rosette on the surface of the platform central pillar, and an FBG temperature sensor is installed close to those strain sensors for temperature compensation. The FBG sensors have been in operation for one year without any significant reduction of working performance. Strain responses induced by the impacts of ocean waves and the ship's hundred tons of weight are monitored on site successfully. The fundamental frequency of the platform identified by the results of the FBG sensors agrees well with that obtained by theoretical analysis. In the monitoring, FBG sensors exhibit excellent performance and higher tolerance to harsh environments in the long-term real-time health monitoring of ocean offshore platforms.
Optical fiber sensors have received increasing attention in the fields of civil engineering due to their advantages such as explosion proof, immunity to electromagnetic interference and high accuracy, especially fitting for measurement applications in harsh environment. In this paper, a novel FBG (fiber Bragg grating) strain sensor, which was packaged in a 1.2mm stainless steel tube by epoxy resin, was developed. Strain transferring characteristics was conducted in the calibration experiment on the plain concrete beam using universal testing machine. Three tube-packaged strain FBG sensors were applied in the vibration experiment of roller compacted artificial concrete dam model. The strain analysis was done with different work conditions by three dynamic loads of noise, sine wave and random wave. The different parts of roller compacted artificial concrete dams were monitored successfully in elastic strain and split strain by action of dynamic load. The results show that possible fatigue and breakage damages can be monitored conveniently by embedded FBG sensors, and information can be well provided for structure health diagnoses under the action of dynamic load.
Optic fiber Bragg grating sensor is a new type of sensor, which plays an important role in structural healthy monitoring. When the optic fiber Bragg grating sensor is embedded in the structure or adhered to the structure, there is a strain transferring course between structure and sensor for the existence of interlayer. Important factors that affect the strain transferring are conducted on the base of existent theory in this paper. The influencing parameters are the length of the sensor, the thickness, Young's modulus and Poisson's ratio of interlayer. At the same time, different influencing factors on strain transfer rate are discussed in detail. Some useful conclusions are developed, which provide a theoretical basis for future researches and designs.
We develop an analytical model for the relationship between the strain measured by a fiber Bragg grating sensor and the actual structural strain. The values of the average strain transfer rates calculated from the analytical model agree well with available experiment data. Based on the analytical model, the critical adherence length of an optical fiber sensor can be calculated and is determined by a strain lag parameter, which contains both the effects of the geometry and the relative stiffness of the structural components. The analysis shows that the critical adherence length of a fiber sensing segment is the minimum length with which the fiber must be tightly bonded to a structure for adequate sensing. The strain transfer rate of an optical fiber sensor embedded in a multilayered structure is developed in a similar way, and the factors that influence the efficiency of optical fiber sensor strain transferring are discussed. It is concluded that the strain sensed by a fiber Bragg grating must be magnified by a factor (strain transfer rate) to be equal to the actual structural strain. This is of interest for the application of fiber Bragg grating sensors.
Optical fiber sensors have received increasing attention in the fields of aeronautic and civil engineering for their superior ability of explosion proof, immunity to electromagnetic interference and high accuracy, especially fitting for measurement applications in harsh environment. In this paper, a novel FBG (fiber Bragg grating) strain sensor, which was packaged in a 1.2mm stainless steel tube by epoxy resin, was developed. Experiments were conducted on the universal material testing machine to calibrate its strain transferring characteristics. The sensor has the advantages of small size, high precision and flexible use, and demonstrates promising potentials. Ten of tube-packaged strain FBG sensors were applied in the vibration experiment of submarine pipeline model. The strain measured by FBG sensor agrees well with the electric resistance strain sensor.
Optical fiber sensors have received increasing attention in the fields of aeronautic and civil engineering for their superior ability of explosion proof, immunity to electromagnetic interference and high accuracy, especially fitting for measurement applications in harsh environment. In this paper, a novel FBG (fiber Bragg grating) strain sensor, which was packaged in a 1.2mm stainless steel tube by epoxy resin, was developed. Experiments were conducted on the universal material testing machine to calibrate its strain transferring characteristics. The sensor has the advantages of small size, high precision and flexible use, and demonstrates promising potentials. Ten of tube-packaged strain FBG sensors were applied in the vibration experiment of submarine pipeline model. The strain measured by FBG sensor agrees well with the electric resistance strain sensor.
This paper discusses of the monitoring of the temperature distribution by an optical fiber Bragg grating sensor system. The sensors are embedded in a pipe underground. Ground-source heat pump system utilizes the thermal energy of the underground soil to heat or cool a building. Optical fiber Bragg grating sensors are used to measure the temperature distribution of the soil and the thermal difference of the circulating water system. The sensors were designed and packaged delicately to eliminate the influence of strain as well as to improve the thermal sensitivity. Three Bragg grating sensors were placed at intervals of five meters in a deep well with a length of 25 meters. Data were collected immediately after the installation of the water pipes using a commercial FBG interrogation system. The ultimate purposes of these tests are to measure the water temperature fluctuation along the pipe at the places where the sensors were installed during the operation of the ground source heat pump system, and evaluate the reliability of FBG sensor system for a long period.
Optical fiber sensors show superior potential for structural health monitoring of civil structures to ensure their structural integrity, durability and reliability. Apparent advantages of applying fiber optic sensors to a marine structure include fiber optic sensors’ immunity of electromagnetic interference and electrical hazard when used near metallic elements over a long distance. The strains and accelerations of the newly proposed model of a single post jacket offshore platform were monitored by fiber Bragg grating (FBG) sensors. These FBG sensors were attached to the legs and the top of the platform model in parallel with electric strain gauges or traditional piezoelectric accelerometers, respectively. Experiments were conducted under a variety of loading conditions, including underwater base earthquake simulation dynamic tests and static loading tests. Underwater seismic shaking table was utilized to provide the appropriate excitations. The natural frequencies measured by the FBG accelerometer agree well with those measured by piezo-electrical accelerometers. The monitoring network shows the availability of applying different fiber optic sensors in long-distance structural health monitoring with frequency multiplexing technology. Finally, the existing problems of packaging, strain transferring ratio between the bare fiber and the host structure on which the fiber embedded, and installation and protection of fiber optic sensors are emphasized.
This paper describes a novel fiber-optic level sensor designed to measure the level of benzene, diesel oil and other chemical liquid discretely or continuously. It is an intensity-modulated on-off switching sensor whose operating principle is based on the frustrated-total-internal-reflection effect caused by the refraction index change of the surrounding medium. The sensor head is made from standard multi-mode communication silica fiber with a taper tip. Different tip shapes and fabrication methods were studied and the maximum signal contrast of 15 dB of the sensor tip has been obtained. The experiment results demonstrated that the resolution of the system of 10?m and the level measurement accuracy of ±0.5 mm have been achieved in a continuous measurement range of 2m.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.