In-fibre Bragg grating (FBG) sensors are one of the most exciting developments in the field of optical fibre sensors in recent years. Compared with conventional fibre-optic sensors, FBG sensors have a number of distinguishing advantages. Significant progress has been made in applications to strain and temperature measurements. FBG sensors prove to be one of the most promising candidates for fibre-optic smart structures. This article presents a comprehensive and systematic overview of FBG sensor technology regarding many aspects including sensing principles, properties, fabrication, interrogation and multiplexing of FBG sensors. It is anticipated that FBG sensor systems will be commercialized and widely applied in practice in the near future due to the maturity of economical production of FBGs and the availability of cost effective interrogation and multiplexing techniques.

https://iopscience.iop.org/article/10.1088/0957-0233/8/4/002/pdf

In-fibre Bragg grating sensors

In-service structural health monitoring (SHM) of engineering structures has assumed a significant role in assessing their safety and integrity. Fibre Bragg grating (FBG) sensors have emerged as a reliable, in situ, non-destructive tool for monitoring, diagnostics and control in civil structures. The versatility of FBG sensors represents a key advantage over other technologies in the structural sensing field. In this article, the recent research and development activities in structural health monitoring using FBG sensors have been critically reviewed, highlighting the areas where further work is needed. A few packaging schemes for FBG strain sensors are also discussed. Finally a few limitations and market barriers associated with the use of these sensors have been addressed.

Fibre Bragg gratings in structural health monitoring—Present status and applications

The paper provides a state of the art review of guided wave based structural health monitoring (SHM). First, the fundamental concepts of guided wave propagation and its implementation for SHM is explained. Following sections present the different modeling schemes adopted, developments in the area of transducers for generation, and sensing of wave, signal processing and imaging technique, statistical and machine learning schemes for feature extraction. Next, a section is presented on the recent advancements in nonlinear guided wave for SHM. This is followed by section on Rayleigh and SH waves. Next is a section on real-life implementation of guided wave for industrial problems. The paper, though briefly talks about the early development for completeness,. is primarily focussed on the recent progress made in the last decade. The paper ends by discussing and highlighting the future directions and open areas of research in guided wave based SHM.

https://iopscience.iop.org/article/10.1088/0964-1726/25/5/053001/pdf

Guided wave based structural health monitoring: A review

Structural Health Monitoring (SHM) can be understood as the integration of sensing and intelligence to enable the structure loading and damage-provoking conditions to be recorded, analyzed, localized, and predicted in such a way that nondestructive testing becomes an integral part of them. In addition, SHM systems can include actuation devices to take proper reaction or correction actions. SHM sensing requirements are very well suited for the application of optical fiber sensors (OFS), in particular, to provide integrated, quasi-distributed or fully distributed technologies. In this tutorial, after a brief introduction of the basic SHM concepts, the main fiber optic techniques available for this application are reviewed, emphasizing the four most successful ones. Then, several examples of the use of OFS in real structures are also addressed, including those from the renewable energy, transportation, civil engineering and the oil and gas industry sectors. Finally, the most relevant current technical challenges and the key sector markets are identified. This paper provides a tutorial introduction, a comprehensive background on this subject and also a forecast of the future of OFS for SHM. In addition, some of the challenges to be faced in the near future are addressed.

Fiber Optic Sensors in Structural Health Monitoring

Fibre-reinforced composites are rapidly gaining market share in structural applications, but further growth is limited by their lack of toughness. Fibre hybridisation is a promising strategy to toughen composite materials. By combining two or more fibre types, these hybrid composites offer a better balance in mechanical properties than non-hybrid composites. Predicting their mechanical properties is challenging due to the synergistic effects between both fibres. This review aims to explain basic mechanisms of these hybrid effects and describes the state-of-the-art models to predict them. An overview of the tensile, flexural, impact and fatigue properties of hybrid composites is presented to aid in optimal design of hybrid composites. Finally, some current trends in fibre hybridisation, such as pseudo-ductility, are described.

/pdf/fibre-hybridisation-in-polymer-composites-a-review-gcnp0ezsc7.pdf

Fibre hybridisation in polymer composites: a review

Optical fiber sensors are emerging as a superior nondestructive means for condition evaluation of civil structures. The ability of an optical fiber sensor to monitor strain distribution in a structural material depends on the bonding characteristics between the material and the optical fiber. The strain field transferred from the structure to the optical fiber sensor generates changes in the characteristics of the light signal transmitted by the glass core of the optical fiber. Transduction of this signal will provide a means for measurement of strain. However, the mechanical properties of the protective coatings employed in conjunction with optical fibers alter the strain transduction capabilities of the sensor. A portion of the strain is absorbed by the protective coating of the optical fiber, and hence, only a segment of structural strain is sensed. In the study reported here, a model is introduced and tested through which it is possible to interpret the actual level of structural strains from the values measured by an optical fiber sensor. A number of realistic assumptions were introduced to simplify the development of the mathematical rigor. It was determined that the strain transfer characteristics of optical fibers depend on the mechanical properties of the glass core, the protective coating, and the gauge length of the optical fiber. Mathematical expressions are developed through which it is possible to describe the level of strain loss within the protective coating, and the amount transferred to the optical fiber core. The theoretical findings were verified through a series of experiments involving white light interferometry. The investigation encompassed repeated experiments with a range of fiber sensor gauge lengths. The experimental program included evaluation of strain transfer capabilities of coated as well as bare fibers.

Mechanics of bond and interface shear transfer in optical fiber sensors

Implementation of successful civil structural health monitoring strategies requires selection and placement of sensors suitable for measurement of key parameters that influence the performance and health of the structural system. Optical fiber sensors have been successfully implemented in aeronautics, mechanical systems, and medical applications. Civil structures pose further challenges in monitoring mainly due to their large dimensions, diversity as well as heterogeneity of materials involved, and hostile construction environment. This article provides a summary of basic principles pertaining to practical health monitoring of civil engineering structures with optical fiber sensors. The issues discussed include basic sensor principles, strain transfer mechanism, sensor packaging, sensor placement in construction environment, and reliability and survivability of the sensors.

Practical implementation of optical fiber sensors in civil structural health monitoring

The behavior of high-strength concrete subjected to multiaxial states of stress was studied. An experimental program was undertaken to quantitatively determine the failure surface for high-strength concrete. Results from this study provide the means to predict the failure condition for high-strength concrete under combined stresses. The experimental program was comprised of testing high-strength concretes at three different compressive strength levels. The three strength levels included concretes with compressive strengths of 6 ksi (42 MPa), 10 ksi (69 MPa), and 15 ksi (103 MPa). The triaxial tests were performed on 4-by-8 in (100-by-200 mm) cylindrical specimens. The confining pressures employed in the experiments ranged from 1,200 psi (8.3 MPa) to 12,000 psi (82 MPa). A series of uniaxial tension and compression tests were also performed to develop the necessary data for establishment of the failure criterion. Empirical relationships were developed for prediction of axial strength as a function of confining pressure. In general, the axial strength of high-strength concrete increases with increased confining pressure. However, in comparison with the normal-strength concrete, the effect of confining pressure on the failure strength of high-strength concrete is less pronounced.

High - strength concrete subjected to triaxial compression

Foreword Preface Chapter I: Global perspectives on structural health monitoring of civil structures. Are civil structural engineers 'risk averse'? Can civionics help?, A.A. Mufti, B. Bakht, G. Tadros, A.T. Horosko, and G. Sparks Monitoring technologies for maintenance and management of urban highways in Japan, Y. Adachi The role of sensing and measurement in achieving FHWA's strategic vision for highway infrastructure, S.B.Chase Recent development of bridge health monitoring system in Korea, H.M. Koh, S. Kim, and J.F. Choo A strategy to implement structural health monitoring on bridges, C. Sikorsky Sensors - not just for research anymore, N.P. Vitillo Investigation of the dynamic properties of the Brooklyn Bridge, Q. Ye, G. Fanjiang, and B. Yanev Chapter II: Monitoring issues in ancient and modern structures. Distributed sensing technologies for monitoring frpstrengthened structures, Z.S. Wu and C.Q. Yang Problems and perspectives in monitoring of ancient masonry structures, A. De Stefano and R. Ceravolo Monitoring and response of CFRP prestressed concrete bridge, N.F. Grace Design of temporary and permanent arrays to assess dynamic parameters in historical and monumental buildings, P. Clemente and D. Rinaldis FRP-Strengthened structures: Monitoring issues from Quebec applications, P. Labossiere, P. Rochette, K.W. Neale, and M. Demers Structural and material monitoring of historical objects, M. Drdack Chapter III: Sensing of structural parameters and extreme events. Internal and external sensing for post-earthquake evaluation of bridges, M. Saud Saudi, R. Nelson, and P. Laplace Application of em stress sensors in large steel cables, M.L.Wang, G. Wang, and Y. Zhao Enhancing durability of structures by monitoring strain and cracking behavior, B. Hillemeier, H. Scheel, and W. Habel Development of an earthquake damage detection system for bridge structures, H. Kobayashi andS. Unjoh Determination of rebar forces based on the exterior crack opening displacement measurement of reinforced concrete, T. Matsumoto and M.N. Islam Monitoring system based on optical fiber sensing technology for tunnel structures and other infrastructure, K. Fujihashi, K. Kurihara, K. Hirayama, and S. Toyoda Development of FBG sensors for structural health monitoring in civil infrastructures, Z. Zhou and J. Ou Chapter IV: Smart sensors, imaging and NDT of civil structures. Monitoring of a smart concrete beam, Q.B. Li, L. Li, and F. Zhang Fiber optic nerve systems with optical correlation domain technique for smart structures and smart materials, K. Hotate Use of active sensors for health monitoring of transportation infrastructure, S. Nazarian Health monitoring of concrete structures using self-diagnosis materials, H. Inada, Y. Okuhara, and H. Kumagai Application of image analysis to steel structural engineering, K. Tateishi and T. Hanji Shape memory alloy based smart civil structures with self-sensing and repairing capabilities, H. Li, C. Mao, Z. Liu, and J. Ou Smart sensors and integrated SHM system for offshore structures, Z. Duan, J. Ou, Z. Zhou, and X. Zhao Chapter V: Sensor system design, data quality, processing, and interpretation. Design considerations for sensing systems to ensure data quality, R. Zhang and E. Aktan Practical implementations of intelligent monitoring systems in HIT, J.Ou Health monitoring, damage prognosis and service-life prediction - issues related to implementation, V.M. Karbhari Adaptive event detection for shm system monitoring, D.K. McNeill and L. Card A note on interpretation of shm data for bridges, B. Bakht Chapter VI: Sensor and instrumentation performance and reliability instrumentation performance during long-term bridge monitoring, I.N. Robertson, G.P. Johnson, and S. Wang Stability and reliability of fiber-optic measurement systems -

Farhad Ansari

Papers

Mechanics of bond and interface shear transfer in optical fiber sensors

Practical implementation of optical fiber sensors in civil structural health monitoring

High - strength concrete subjected to triaxial compression

Sensing issues in civil structural health monitoring

Structural health monitoring of civil infrastructure systems