Abstract
Distributed fibre optic sensors (DFOS) are popular for structural health monitoring applications in large engineering infrastructure because of their ability to provide spatial strain measurements continuously along their lengths. Curved paths, particularly semicircular paths, are quite common for optical fibre placement in large structures in addition to straight paths. Optical fibre sensors embedded in a curved path configuration typically measure a component of strain, which often cannot be validated using traditional approaches. Thus, for most applications, strain measured along curved paths is ignored as there is no proper validation tool to ensure the accuracy of the measured strains. To overcome this, an analytical strain transformation equation has been developed and is presented here. This equation transforms the horizontal and vertical strain components obtained along a curved semicircular path into a strain component, which acts tangentially as it travels along the curved fibre path. This approach is validated numerically and experimentally for a DFOS installed on a steel specimen with straight and curved paths. Under tensile and flexural loading scenarios, the horizontal and vertical strain components were obtained numerically using finite element analysis and experimentally using strain rosettes and then, substituted into the proposed strain transformation equation for deriving the transformed strain values. Subsequently, the derived strain values obtained from the proposed transformation equation were validated by comparing them with the experimentally measured DFOS strains in the curved region. Additionally, this study has also shown that a localised damage to the DFOS coating will not impact the functionality of the sensor at the remaining locations along its length. In summary, this paper presents a valid strain transformation equation, which can be used for transforming the numerical simulation results into the DFOS measurements along a semicircular path. This would allow for a larger scope of spatial strains measurements, which would otherwise be ignored in practice.
Highlights
IntroductionStructural health monitoring (SHM) consists of integrating the sensor devices with the structural components to extract continuous information related to the mechanical behaviour of a structure in various operational conditions [5,6]
Surface strains on a structure are usually measured using foil strain gauges (FSG)/strain rosettes (SR), which are considered as a mature technology
The Distributed fibre optic sensors (DFOS) is laid ononthe surface of a structure for measuring strains in the form of straight lines connected the surface of a structure measuring strains in the form of straight lines connected between loops.Usually, Usually,thethe strains along curved region the DFOS
Summary
SHM consists of integrating the sensor devices with the structural components to extract continuous information related to the mechanical behaviour of a structure in various operational conditions [5,6]. Different types of sensors such as microelectromechanical systems (MEMS), accelerometers, optical fibres, vibration sensors, pressure-based sensors [7], and global positioning system (GPS) sensors [8] can be used during the SHM process for measuring a wide range of critical structural parameters, such as strain, temperature, displacement, pressure, and vibration [9]. FSGs are discrete sensors and can only provide localised strain values at locations close to the gauge [12], and they cannot be used for long-term SHM applications [13].
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