Weight data of vehicles play an important role in traffic planning, weight enforcement, and pavement condition assessment. In this paper, a weigh-in-motion (WIM) system that functions at both low-speeds and high-speeds in flexible pavements is developed based on in-pavement, three-dimensional glass-fiber-reinforced, polymer-packaged fiber Bragg grating sensors (3D GFRP-FBG). Vehicles passing over the pavement produce strains that the system monitors by measuring the center wavelength changes of the embedded 3D GFRP-FBG sensors. The FBG sensor can estimate the weight of vehicles because of the direct relationship between the loading on the pavement and the strain inside the pavement. A sensitivity study shows that the developed sensor is very sensitive to sensor installation depth, pavement property, and load location. Testing in the field validated that the longitudinal component of the sensor if not corrected by location has a measurement accuracy of 86.3% and 89.5% at 5 mph and 45 mph vehicle speed, respectively. However, the system also has the capability to estimate the location of the loading position, which can enhance the system accuracy to more than 94.5%.
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A constrained cylinder model of strain transfer for packaged fiber Bragg grating sensors embedded in inelastic medium
In this study, the strain transfer rate from an axially loaded, inelastic concrete tube to a glass fiber reinforced polymer (GFRP) packaged optical fiber with Bragg gratings is derived when the radial deformation of an “equivalent elastic” concrete tube is constrained by the packaged fiber. The concrete strains, both undisturbed and disturbed by the presence of the fiber Bragg gratings sensor, are analytically evaluated, and their difference (up to over 30%) is related to the development length at two free ends of the GFRP package. The mechanism of strain transfer is dominated by a ratio of average fiber and concrete strains in elastic range and by the averaging effect and a ratio of disturbed and undisturbed concrete strains in inelastic range. The analytical strain transfer rate was significantly reduced from 0.95, when concrete behaved elastically, to less than 0.4, when concrete damaged severely. This result was experimentally validated with less than 10% difference prior to concrete fracture. The validated model is applicable to fiber optic sensors that are embedded into concrete structures by a concrete cover of at least 10 times of the radius of the optic fiber.
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- Award ID(s):
- 1750316
- NSF-PAR ID:
- 10089615
- Date Published:
- Journal Name:
- Structural Control and Health Monitoring
- ISSN:
- 1545-2255
- Page Range / eLocation ID:
- e2335
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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This study presents an experimental investigation on the combined effect of mechanical loads and corrosion using the designed polytetrafluoroethylene tube-packaged fiber Bragg grating (FBG) sensors, as to implement long-gauge FBG (LFBG) sensors in corrosion detection practices for structural health monitoring. A simplified LFBG-based sensing model was proposed for strain measurement in terms of the Bragg wavelength change. Correspondingly, a systematic corrosion assessment strategy was developed to estimate corrosion severity and average corrosion rate. Upon this, the experimental study was performed on epoxy-coated steel specimens embedded with LFBG sensors, where the loading, corrosion, and combined loading–corrosion tests were used to explore the effect of mechanical loads on corrosion behavior. Test results revealed that the specimens subjected to combined conditions exhibited more severe corrosion damage. The maximum mass loss was observed to be 1.82 and 2.43 in percentage under individual corrosion and combined loading–corrosion conditions, respectively. Also, the pit depth under combined conditions was found to develop rapidly in the early stage. The pit depth severity ratio was around 0.2–0.8 during the 67 days of exposure, indicating an evident impact of loading on corrosion severity. Furthermore, the maximum average corrosion rate under combined conditions was found to be 5.66 times that under individual corrosion conditions.
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Quantitative dynamic strain measurements of the ground would be useful for engineering scale problems such as monitoring for natural hazards, soil-structure interaction studies, and non-invasive site investigation using full waveform inversion (FWI). Distributed acoustic sensing (DAS), a promising technology for these purposes, needs to be better understood in terms of its directional sensitivity, spatial position, and amplitude for application to engineering-scale problems. This study investigates whether the physical measurements made using DAS are consistent with the theoretical transfer function, reception patterns, and experimental measurements of ground strain made by geophones. Results show that DAS and geophone measurements are consistent in both phase and amplitude for broadband (10 s of Hz), high amplitude (10 s of microstrain), and complex wavefields originating from different positions around the array when: (1) the DAS channels and geophone locations are properly aligned, (2) the DAS cable provides good deformation coupling to the internal optical fiber, (3) the cable is coupled to the ground through direct burial and compaction, and (4) laser frequency drift is mitigated in the DAS measurements. The transfer function of DAS arrays is presented considering the gauge length, pulse shape, and cable design. The theoretical relationship between DAS-measured and pointwise strain for vertical and horizontal active sources is introduced using 3D elastic finite-difference simulations. The implications of using DAS strain measurements are discussed including directionality and magnitude differences between the actual and DAS-measured strain fields. Estimating measurement quality based on the wavelength-to-gauge length ratio for field data is demonstrated. A method for spatially aligning the DAS channels with the geophone locations at tolerances less than the spatial resolution of a DAS system is proposed.more » « less
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null (Ed.)Structural health monitoring (SHM) activities are essential for achieving a realistic characterisation of bridge structural performance levels throughout the service life. These activities can help detect structural damage before the potential occurrence of component- or system-level structural failures. In addition to their application at discrete times, SHM systems can also be installed to provide long-term accurate and reliable data continuously throughout the entire service life of a bridge. Owing to their superior accuracy and long-term durability compared to traditional strain gages, fiber optic sensors are ideal in extracting accurate real-time strain and temperature data of bridge components. This paper presents a statistical damage detection and localisation approach to evaluate the performance of prestressed concrete bridge girders using fiber Bragg grating sensors. The presented approach employs Artificial Neural Networks to establish a relationship between the strain profiles recorded at different sensor locations across the investigated girder. The approach is capable of detecting and localising the presence of damage at the sensor location without requiring detailed loading information; accordingly, it can be suitable for long-term monitoring activities under normal traffic loads. Experimental laboratory data obtained from the structural testing of a large-scale prestressed concrete bridge girder is used to illustrate the approach.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1002/stc.2335
