| 1. |
- Bado, Mattia Francesco, et al.
(author)
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Characterization of concrete shrinkage induced strains in internally-restrained RC structures by distributed optical fiber sensing
- 2021
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In: Cement and Concrete Composites. - : Elsevier BV. - 0958-9465. ; 120
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Journal article (peer-reviewed)abstract
- The present paper reports the result of an inter-university experimental investigation on concrete shrinkage induced strains on embedded rebars instrumented with Distributed Optical Fiber Sensors (DOFS). The monitoring was performed for a standard 28 days drying time and for a shorter 6 days time span (reflecting realistic constructions schedules accelerations to meet set deadlines). The tested specimens were Reinforced Concrete (RC) tensile members differing in their geometry, DOFS employed and fiber/rebar bonding techniques. Regarding the latter, a combination of cyanoacrylate (for gluing) and silicone (protection) was found to be the optimal one for deployments inside RC structures. The DOFS-reported combined effect of concrete shrinkage and creep on the embedded rebars is compared with the Model Code 2010's predictions and employed to extract conclusions on the residual performance of the RC members at the end of their drying phase.
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| 2. |
- Blomfors, Mattias, 1990, et al.
(author)
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Incorporation of pre-existing cracks in finite element analyses of reinforced concrete beams without transverse reinforcement
- 2021
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In: Engineering Structures. - : Elsevier BV. - 1873-7323 .- 0141-0296. ; 229
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Journal article (peer-reviewed)abstract
- Cracking in reinforced concrete (RC) bridges and other structures is common and not necessarily detrimental. However, some cracks may grow past specified limits and, aside from aesthetic and durability aspects, may influence the ductility and structural capacity of an RC member. This is not generally reflected in current assessment methods and, therefore, improved methods are needed. The aim of the current work was to develop a modelling methodology to incorporate pre-existing cracks into finite (FE) analysis for improved structural assessments. Two different approaches were investigated: (1) weakening the continuum elements at the position of a crack and (2) introducing discrete crack elements with weakened properties. In both approaches, a total-strain based model was used in the continuum elements. These modelling approaches were applied to analyses of experiments, in which concrete beams had been pre-cracked and tested in four-point bending. The pre-existing cracks led to differing failures limiting the deformation capacity, plus varying ultimate capacity and ductility. In the current study the weakened-elements approach captured the failure characteristics, ultimate capacity and ductility more accurately than a standard FE analysis without cracks included; the discrete-crack approach, on the other hand, did not. Furthermore, the bending stiffness differed between the experimental tests and the FE analyses. Damaged bond properties and closure of cracks in the compressive zone were identified as probable causes. Moreover, the choice of shear retention used for the weakened elements was shown to noticeably affect the predicted capacity and ductility. In conclusion, the weakened-elements approach was the most straightforward to implement. It was less time-consuming and led to better agreement with experimental results, compared to the discrete-crack approach. Based on this study, the weakened-elements approach is regarded as a promising approach for the structural assessments of tomorrow.
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| 3. |
- Chen, Teresa E, 1988, et al.
(author)
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Corrosion Pattern and Mechanical Behaviour of Corroded Rebars in Cracked Plain and Fibre Reinforced Concrete
- 2021
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In: RILEM Bookseries. - Cham : Springer International Publishing. - 2211-0844 .- 2211-0852. ; 30, s. 477-488
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Conference paper (peer-reviewed)abstract
- This paper presents experimental results of corrosion pattern and tensile behaviour of corroded rebars extracted from 4 uncracked and 18 pre-cracked plain concrete and fibre reinforced concrete (FRC) beams. The beams were pre-cracked through three-point bending to a target maximum crack width of 0.1 and 0.4 mm, and then subjected to natural corrosion through cyclic exposure to a 16.5% NaCl solution for more than three years. 3D-scanning was used to characterise the pit morphology and evaluate the maximum local corrosion level of extracted rebars. Under the same loading condition and crack width, most rebars in FRC had smaller maximum local corrosion level than those in plain concrete. Subsequently, tensile tests were carried out on the extracted rebars, with Digital Image Correlation (DIC) technique adopted to investigate the influence of pit morphology on the local strain development. Finally, the time-dependent influence of transverse and longitudinal cracks on the pit morphology which governs the ultimate strain of corroded rebars was discussed. The time-varying nature of corrosion morphology should be considered when predicting the durability and long-term safety of conventional reinforced concrete and FRC structures with reinforcing bars under chloride environments.
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| 4. |
- Fernandez, Ignasi, 1984, et al.
(author)
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Long-term performance of distributed optical fiber sensors embedded in reinforced concrete beams under sustained deflection and cyclic loading
- 2021
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In: Sensors. - : MDPI AG. - 1424-8220. ; 21:19
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Journal article (peer-reviewed)abstract
- This paper explores the performance of distributed optical fiber sensors based on Rayleigh backscattering for the monitoring of strains in reinforced concrete elements subjected to different types of long-term external loading. In particular, the reliability and accuracy of robust fiber optic cables with an inner steel tube and an external protective polymeric cladding were investigated through a series of laboratory experiments involving large-scale reinforced concrete beams subjected to either sustained deflection or cyclic loading for 96 days. The unmatched spatial resolution of the strain measurements provided by the sensors allows for a level of detail that leads to new insights in the understanding of the structural behavior of reinforced concrete specimens. Moreover, the accuracy and stability of the sensors enabled the monitoring of subtle strain variations, both in the short-term due to changes of the external load and in the long-term due to time-dependent effects such as creep. Moreover, a comparison with Digital Image Correlation measurements revealed that the strain measurements and the calculation of deflection and crack widths derived thereof remain accurate over time. Therefore, the study concluded that this type of fiber optic has great potential to be used in real long-term monitoring applications in reinforced concrete structures.
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| 5. |
- Gil Berrocal, Carlos, 1986, et al.
(author)
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A fiber optics enriched Digital Twin for assessment of reinforced concrete structures
- 2021
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In: IABSE Congress, Ghent 2021: Structural Engineering for Future Societal Needs. ; , s. 382-390
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Conference paper (peer-reviewed)abstract
- This paper presents the results of SensIT, an ongoing research initiative at Chalmers University of Technology aimed at developing a digital twin concept to improve the asset management strategies of reinforced concrete infrastructure. The developed concept relies on data collected from distributed optical fiber sensors (DOFS), which are then analysed to extract relevant features, such as deflections and crack widths, that can be used as indicators of the structural performance. Thereafter, intuitive contour plots are generated to deliver critical information about the element's structural condition in a clear and straightforward manner. Last, both raw and analysed data are integrated into a collaborative web application where information can be readily accessed, and results can be visualized directly onto a 3D model of the element. The concept has been tested on a large-scale reinforced concrete beam subjected to flexural loading in laboratory conditions.
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| 6. |
- Gil Berrocal, Carlos, 1986, et al.
(author)
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Assessment and visualization of performance indicators of reinforced concrete beams by distributed optical fibre sensing
- 2021
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In: Structural Health Monitoring. - : SAGE Publications. - 1475-9217 .- 1741-3168. ; 20:6, s. 3309-3326
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Journal article (peer-reviewed)abstract
- The implementation of structural health monitoring systems in civil engineering structures already in the construction phase could contribute to safer and more resilient infrastructure. Due to their lightweight, small size and high resistance to the environment, distributed optical fibre sensors stand out as a very promising technology for damage detection and quantification in reinforced concrete structures. In this article, the suitability of embedding robust distributed optical fibre sensors featuring a protective sheath to accurately assess the performance indicators, in terms of vertical deflection and crack width, of three reinforced concrete beams subjected to four-point bending is investigated. The results revealed that a certain strain attenuation occurs in embedded robust distributed optical fibre sensors compared to commonly used thin polyimide-coated distributed optical fibre sensors bonded to steel reinforcement bars. However, the presence of the protective sheath prevented the appearance of strain reading anomalies which has been a frequently reported issue. Performance wise, the robust distributed optical fibre sensors were able to provide a good estimate of the beam deflections with errors of between 12.3% and 6.5%. Similarly, crack widths computed based on distributed optical fibre sensor strain measurements differed by as little as ±20 µm with results from digital image correlation, provided individual cracks could be successfully detected in the strain profiles. Finally, a post-processing procedure is presented to generate intuitive contour plots that can help delivering critical information about the element’s structural condition in a clear and straightforward manner.
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| 7. |
- Gil Berrocal, Carlos, 1986, et al.
(author)
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Crack monitoring in reinforced concrete beams by distributed optical fiber sensors
- 2021
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In: Structure and Infrastructure Engineering. - : Informa UK Limited. - 1573-2479 .- 1744-8980. ; 17:1, s. 124-139
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Journal article (peer-reviewed)abstract
- This paper investigates the use of distributed optical fiber sensors (DOFS) based on Optical Frequency Domain Reflectometry of Rayleigh backscattering for Structural Health Monitoring purposes in civil engineering structures. More specifically, the results of a series of laboratory experiments aimed at assessing the suitability and accuracy of DOFS for crack monitoring in reinforced concrete members subjected to external loading are reported. The experiments consisted on three-point bending tests of concrete beams, where a polyamide-coated optical fiber sensor was bonded directly onto the surface of an unaltered reinforcement bar and protected by a layer of silicone. The strain measurements obtained by the DOFS system exhibited an accuracy equivalent to that provided by traditional electrical foil gauges. Moreover, the analysis of the high spatial resolution strain profiles provided by the DOFS enabled the effective detection of crack formation. Furthermore, the comparison of the reinforcement strain profiles with measurements from a digital image correlation system revealed that determining the location of cracks and tracking the evolution of the crack width over time were both feasible, with most errors being below +/- 3 cm and +/- 20 mu m, for the crack location and crack width, respectively.
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