Purpose – The purpose of this paper is to investigate an online monitoring strategy that incorporates fiber Bragg gratings (FBGs) for deformation displacement detection, with the background that slope deformation monitoring is crucial to engineering safety supervision and disaster prevention. Design/methodology/approach – A “beam element” method has been proposed, introduced and experimentally verified in detail. The deformation displacement along a flexible bar can be obtained based on this method, using the distributed strain detected by the FBGs embedded in the bar. A novel sensor structure containing inclinometer casings and a series of connected flexible pipes with FBGs embedded has been proposed. Based on the features of this structure, two FBG deformation sensors have been manufactured and installed into a slope. A matched monitoring station which permits real-time supervision, warning and remote access across the Internet was established and operated. Findings – Displacement data from September 2013 to August 2014 are obtained, which is basically consistent with the practical situation. Originality/value – The FBG deformation sensors demonstrated a robust and reliable measurement performance, which is promising for real-time disaster warning in slope engineering.

Abstract:The theoretical design method of enhanced sensitivity fiber grating (FBG) strain sensors was given, and moreover high qualified strain sensors were developed and fabricated, whose sensing properties were good for practical applications. The strain sensor with cylindrical shell encapsulation contained three tubular structures, due to the uneven surface structure, in the area of the strain concentration, improving the sensitivity. It could achieve the embedment strain measurement and surface measurement and had the advantages of the easy installation. The good agreement was obtained between the measurements and theoretical simulation results. After each calibration test, twenty-four FBG strain sensors and six FBG temperature compensation sensors have been installed on the undersurface of the box girder of Diaoshuiyan bridge in Yongtaiwen highway. Finally, we built up a long-term structure health system for the highway bridge.

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Purpose – This paper aims to present an effective sensing detection system based on fiber Bragg grating (FBG) sensing technology for protective barriers that have been effectively applied to intercept and stop rocks from falling onto railway tracks. . Determination of exact stress and deformation values during impact tests for key components of the protective barrier forms important criteria for quality control of these barriers. Monitoring changes in force along the protective barrier when deployed in field application allows for real-time disaster warning for collapse and falling rocks. Design/methodology/approach – In this paper, we propose a monitoring strategy for key components of a protective barrier. During performance tests, dynamic force and strain were measured for the steel strands and supporting I-beam, respectively. Design of a special elastic structure for the force transducer based on finite element analysis and tensile tests has been discussed here. Two types of FBG force transducers were manufactured based on the elastic structure. Four FBG force transducers and four FBG strain sensors were used for impact verification testing of a new rigid protective barrier with a design protection level of 25 KJ. Findings – Dynamic force and strain responses were obtained during an impact of free-falling block with a kinetic energy of 25 KJ. Originality/value – The FBG monitoring scheme can be extremely valuable for optimized design of the barrier and can provide real-time disaster warning in regions of collapse and falling rocks.

A fiber Bragg grating (FBG) sensing network with a bus chain typology structure based on time-division multiplexing (TDM) technology has been developed. Each FBG sensor was placed in an isolated branching circuit separated by an optical splitter. By doing this, multiple reflection and spectrum shadow, which are common in a traditional TDM network, were eliminated since incident light reflected by each sensor did not go through the other sensors. Interference among different FBGs was also avoided. The system was experimentally verified by constructing such a network with 17 FBGs involved. Wavelength and position interrogation were successfully realized. Temperature experiment was carried out on four of the FBGs and the sensitivity was 9. 87, 9.92, 9.91, and 9.97 pm∕°C, respectively. The durability, reliability, and measuring accuracy of the sensing network were effectively improved due to the bus chain typology structure.