Estimation of Tendon Force Distribution in Prestressed Concrete Girders Using Smart Strand

Cho, Keunhee; Kim, Sung Tae; Cho, Jeong-Rae; Park, Young-Hwan

doi:10.3390/app7121319

Cited by 7 publications

(7 citation statements)

References 12 publications

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“…If a temperature gradient occurs in a no-stress state, the relationship between the wavelength and the strain change can be derived as equations (8) and (9) from equation 1for the bare optical FBG and equation 2for the smart rod, respectively.…”

Section: Thermal Expansion Coefficient Of the Smart Rodmentioning

confidence: 99%

“…With the thermal expansion coefficient α f being 0:5 × 10 −6 /°C for the bare optical fibre made of SiO 2 , the unknowns in equations (8) and (9) are the thermooptic coefficient ξ and the thermal expansion coefficient α h of the host material. As shown in Figure 5, a temperature test was performed on the bare optical fibre and the smart rod in order to determine the thermooptic coefficient ξ of the smart rod and the thermal expansion coefficient α h of the material hosting the FBG in the smart rod.…”

Section: δλ λmentioning

confidence: 99%

“…A FBG-embedded CFRP rod (smart rod, thereafter) is proposed to solve these problems, which provides extra protection for the optical fibre and also perfect bondage between the sensor and concrete [6]. This smart rod was utilized to measure the prestress force in a PSC (prestressed concrete) structure by disposing the smart rod instead of the core wire of the strand [7,8]. The smart rod thus played both the roles of the sensor and the core wire of the strand.…”

Section: Introductionmentioning

confidence: 99%

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Measurement of Mechanical and Thermal Strains by Optical FBG Sensors Embedded in CFRP Rod

et al. 2019

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The present study intends to provide the photoelastic coefficient and thermal expansion coefficient needed to use an FBG-embedded CFRP rod (smart rod) as strain sensor. Due to the monolithic combination of the FBG sensor with a CFRP rod, the smart rod is likely to exhibit thermal and mechanical properties differing from those of the bare FBG sensor. A tensile test showed that the photoelastic coefficient of the smart rod is 0.204, which is about 7.3% lower than the 0.22 value of the bare optical FBG. Moreover, the thermal expansion coefficient of the smart rod obtained through a thermal test appeared to be negative with a low value of −0.190×10−6/°C. Consequently, the temperature dependence of the smart rod is mainly expressed by means of the thermooptic coefficient. Compared to the bare FBG sensor, the smart rod is easier to handle and can measure compressive strains, which make it a convenient sensor for various concrete structures.

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Section: Thermal Expansion Coefficient Of the Smart Rodmentioning

confidence: 99%

Section: δλ λmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Measurement of Mechanical and Thermal Strains by Optical FBG Sensors Embedded in CFRP Rod

et al. 2019

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“…However, prestress losses can be directly, simply, and accurately determined over time if the internal tendons of PC girders are instrumented by load cells, vibrating wire strain gauges, or elasto-magnetic sensors during construction [10][11][12][13]. Besides, FBG sensors can be embedded in seven-wire strands along PC girders for long term monitoring of tensile forces [14,15]. Although instrumentation of external tendons is easy during their serviceability, NonDestructive Testing (NDT) methods are required.…”

Section: Introductionmentioning

confidence: 99%

State-of-the-Art Review on Determining Prestress Losses in Prestressed Concrete Girders

2020

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Prestressing methods were used to realize long-span bridges in the last few decades. For their predictive maintenance, devices and dynamic nondestructive procedures for identifying prestress losses were mainly developed since serviceability and safety of Prestressed Concrete (PC) girders depend on the effective state of prestressing. In fact, substantial long term prestress losses can induce excessive deflections and cracking in large span PC bridge girders. However, old unsolved problematics as well as new challenges exist since a variation in prestress force does not significantly affect the vibration responses of such PC girders. As a result, this makes uncertain the use of natural frequencies as appropriate parameters for prestress loss determinations. Thus, amongst emerging techniques, static identification based on vertical deflections has preliminary proved to be a reliable method with the goal to become a dominant approach in the near future. In fact, measured vertical deflections take accurately and instantaneously into account the changes of structural geometry of PC girders due to prestressing losses on the equilibrium conditions, in turn caused by the combined effects of tendon relaxation, concrete creep and shrinkage, and parameters of real environment as, e.g., temperature and relative humidity. Given the current state of quantitative and principled methodologies, this paper represents a state-of-the-art review of some important research works on determining prestress losses conducted worldwide. The attention is principally focused on a static nondestructive method, and a comparison with dynamic ones is elaborated. Comments and recommendations are made at proper places, while concluding remarks including future studies and field developments are mentioned at the end of the paper.

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“…Two kinds of FBG sensors have been proposed for prestress monitoring. The first type is named as “smart strand” consisting of six helical wires and a core wire embedded an FBG sensor [29,30,31,32,33]. Although the FBG sensor can accurately measure prestress in the core wire, the “smart strand” also has two drawbacks in practice.…”

Section: Introductionmentioning

confidence: 99%

Evaluation of Prestress Loss Distribution during Pre-Tensioning and Post-Tensioning Using Long-Gauge Fiber Bragg Grating Sensors

Shen

Wang

et al. 2018

Sensors

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Prestress loss evaluation in prestressed strands is essential for prestressed structures. However, the sensors installed outside the duct can only measure the total prestress loss. The sensors attached on strands inside the duct also have several problems, such as inadequate durability in an aggressive environment and vulnerability to damage during tensioning. This paper proposes a new installation method for long-gauge fiber Bragg grating (LFBG) sensors to prevent accidental damage. Then the itemized prestress losses were determined in each stage of the pre-tensioning and post-tensioning according to the LFBG measurements. We verified the applicability of the LFBG sensors for prestress monitoring and the accuracy of the proposed prestress loss calculation method during pre-tensioning and post-tensioning. In the pre-tensioning case, the calculated prestress losses had less deviation from the true losses than those obtained from foil-strain gauges, and the durability of the LFBG sensors was better than foil-strain gauges, whereas in post-tensioning case, the calculated prestress losses were close to those derived from theoretical predictions. Finally, we monitored prestress variation in the strand for 90 days. The itemized prestress losses at each stages of post-tensioning were obtained by the proposed calculation method to show the prospect of the LFBG sensors in practical evaluation.

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Estimation of Tendon Force Distribution in Prestressed Concrete Girders Using Smart Strand

Cited by 7 publications

References 12 publications

Measurement of Mechanical and Thermal Strains by Optical FBG Sensors Embedded in CFRP Rod

Measurement of Mechanical and Thermal Strains by Optical FBG Sensors Embedded in CFRP Rod

State-of-the-Art Review on Determining Prestress Losses in Prestressed Concrete Girders

Evaluation of Prestress Loss Distribution during Pre-Tensioning and Post-Tensioning Using Long-Gauge Fiber Bragg Grating Sensors

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