Analysis of Long-Term Prestress Loss in Prestressed Concrete (PC) Structures Using Fiber Bragg Grating (FBG) Sensor-Embedded PC Strands

This study aims to develop a prestressed concrete steel (PC) strand with an embedded optical Fiber Bragg Grating (FBG) sensor, which has been developed by the Korea Institute of Civil Engineering and Building Technology since 2013. This new strand is manufactured by replacing the steel core of the normal PC strand with a carbon-fiber-reinforced polymer (CFRP) rod with excellent tensile strength and durability. Because this new strand is manufactured using the pultrusion method, which is a composite material manufacturing process, with an optical fiber sensor embedded in the inner center of the CFRP Rod, it ensures full composite action as well as proper function of the sensor. In this study, a creep test for maintaining a constant load and a relaxation test for maintaining a constant displacement were performed on the proposed sensor-type PC strand. Each of the two tests was conducted for more than 1000 h, and the long-term performance verification of the sensor-type PC strand was only completed by comparing the performance with that of a normal PC strand. The test specimens were fabricated by applying an optical fiber sensor-embedded PC strand, which had undergone long-term performance verification tests, to a reinforced concrete beam. Depending on whether grout was injected in the duct, the specimens were classified into composite and non-composite specimens. A hydraulic jack was used to prestress the fabricated beam specimens, and the long-term change in the prestress force was observed for more than 1600 days using the embedded optical fiber sensor. The experimental results were compared with the analytical results to determine the long-term prestress loss obtained through finite-element analysis based on various international standards.

Cladding Modified Fiber Bragg Grating for Copper Ions Detection

This paper reports a fiber Bragg grating (FBG) as a biosensor. The FBGs were etched using a chemical agent,namely,hydrofluoric acid (HF). This implies the removal of some part of the cladding layer. Consequently, the evanescent field propagating out of the core will be closer to the environment and become more sensitive to the change in the surrounding. The proposed FBG sensor was utilized to detect toxic heavy metal ions aqueous medium namely, copper ions (Cu2+). Two FBG sensors were etched with 20 and 40 μm diameters and fabricated. The sensors were studied towards Cu2+ with different concentrations using wavelength shift as a result of the interaction between the evanescent field and copper ions. The FBG sensors showed a good response in terms of significant wavelength shift in corresponding to varying Cu2+ concentrations when immersed in aqueous mediums. The sensors exhibited excellent repeatability towards Cu ions.The results demonstrate that the smaller FBG etching diameter, the better optical response in terms of wavelength and linearity.

Research on Networking Algorithm of Distributed FBG Sensor Network

The status monitoring of industrial process equipment is of great significance to its production energy efficiency and safety. A state monitoring system for complex surface structures based on the distributed FBG sensor network is proposed. The system adopts the FBG network and realizes the calculation of the stress field of the complex surface through the FBG layout design at different positions in the three-dimensional space. A 32-channel FBG sensor network is designed, and the light source, demodulation module, and processing system are selected and analyzed. On the basis of building the FBG sensor network, the stress field test was carried out on the industrial process equipment. For complex three-dimensional surface structures, an optical scanner is used for position offset calibration. Experiments show that when force is applied to the center point, the slope of the FBG at the best sensitive position is 0.715 pm/N; when force is applied on both sides, the maximum slope in the positive direction is 0.348 pm/N and the maximum slope in the negative direction is −0.381 pm/N. After data fusion correction is used, the average error of the three-dimensional position offset of the test data is 6.85%. It can be seen that the FBG network has the ability to monitor the state of complex surface structures in the industrial engineering equipment.