• Proceedings of the Korean Geotechical Society Conference
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• 1999.10a
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• pp.397-404
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• 1999

It is essential to measure load transfer mechanism of pile to check the appropriateness of assumptions made for design purpose and to continuously monitor the behavior of pile foundation. Through many attempts to monitor the behavior of super-structure in civil engineering area using several optical fiber sensors have been made, application of optical fiber sensor technology on pile foundation has not been tried up to now. Load transfer of model piles during compression loading was measured by optical fiber sensors and compared with the measurement by strain gauges. Fiber Bragg Grating(FBG) sensor system was used since it has many advantages, such as easy multiplexing, high sensitivity, and simple fabrication. Besides the model pile tests, uniaxial tension test of steel bar and compression tests of mortar specimen were carried out to evaluate the performance of FBG sensors in embedded environments. The shift of refilming wavelength due to the strain in FBG sensor is converted to the strain at sensor location and the dependence between them is 1.28 pm/${\mu}$ strain. FBG sensors embedded in model pile showed a better survivability than strain gauges. Measured results of load transfer by both FBG sensors and strain gauges were similar, but FBG sensors showed a smoother trend than those by strain gauge. Based on the results of model pile test, it was concluded that the use of FBG sensor for strain measurement in pile has a great potential for the analysis of pile load transfer.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2002.05a
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• pp.112-116
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• 2002

In cold forging, the elastic behavior of the die has a direct influence on the accuracy of the forging part. And the die dimension is continuously changed during the loading, unloading, and ejecting stage. In this paper, we evaluated the elastic deflections of cold forging die during loading, unloading, and ejecting stage. Uni-axial strain gauges are used to measure elastic strain of die during each forging stage. Strain gauges are attached on the surface of die. A commercial F.E.M code, DEFORM-2D$\^$TM/ is used to predict elastic strain of die. Two method of F.E.M. analysis are used to compare with measured and calculated elastic strain. One is to regard the die as rigid body over forging cycle. And then, the die sass is analyzed by loading the die with pressure from the forging part. The other is to regard the die as elastic body from forging cycle. The elastic strain of die is calculated and the die is elastically deformed at each strop. The calculated results under the elastic die assumption are well agreed with experimental data using strain gauges.

• Proceedings of the Korea Concrete Institute Conference
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• 1996.04a
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• pp.295-299
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• 1996

Intrinsic Fabry-Perot Optical fiber sensors were embedded to tensile side of the 20cm$\times$20cm$\times$150cm cement concrete structures. The sensors were attached to the reinforcing steels and then, the cement concretes were applied. It took 30 days for curing the specimens. After that, the specimens were tested with 4-point bending method by universal testing machine. Strains were measured and recorded by the strain gauges embedded near optical fiber sensors. Output data of fiber sensor showed good linearity to the strain data from the strain gauges up 2000microstrain. The optical fiber sensors showed good response after yielding of structure while embedded metal film strain gauges did not show any response. We also specimens were broken down. In conclusion, the optical fiber sensors can be used as elements of health monitoring systems for cement concrete infra-structures.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.05a
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• pp.692-695
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• 1999

This paper presents annealing characteristics of CrN thin-film strain gauges, which were deposited on glass by DC reactive magnetron sputtering in an argon-nitrogen atmosphere)Ar-(5-~25%)$N_2$. The physical and electrical characteristics of these films investigated with the thickness range 3500$\AA$ of CrN thin films, annealing temperature (100~30$0^{\circ}C$) and annealing time (24-72hr) . The optimized condition of CrN thin-film strain gauges were thickness range of 3500$\AA$ and annealing condition(30$0^{\circ}C$ , 48hr) in Ar-10%$N_2$ deposition atmosphere. Under optimum conditions, the CrN thin-films for strain gauge is obtained a high resistivity, $\rho$=1147.65$\Omega$cm a low temperature coefficient of 11.17. And change in resistance after annealing for the CrN thin film were quitely linear and stable.

• Journal of the Semiconductor & Display Technology
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• v.14 no.2
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• pp.23-27
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• 2015

In this paper, eco-friendly paper strain gauge was fabricated in the way of printing strain gauge on paper substrate, using PEDOT:PSS ink and inkjet printer technology. As a p-type conductive high polymer, PEDOT:PSS is known to be piezoresistive effect. I formed a strain gauge by connecting in parallel 5 lines of $60{\mu}m$ width printed with PEDOT:PSS. To minimize surrounding influence such as temperature, I formed wheat-stone bridge by combining 4 strain gauges (quarter-bridge strain gauge) which were made up of PEDOT:PSS 5 lines and measured. In quarter-bridge strain gauge, only two strain gauges, facing each other, arranged in strain and horizontal direction were deformed while the other two strain gauge of vertical direction were not. Therefore, quarter-bridge strain gauge showed the output of half bridge. The fabricated quarter-bridge strain gauge had output sensitivity of $105.6{\mu}V/V{\cdot}mm$ and its output linearity was relatively good.

• Computers and Concrete
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• v.20 no.5
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• pp.595-603
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• 2017

Piezoceramic transducers have been widely used in the health monitoring of civil structures. However, in most cases, they are used as sensors either to measure strain or receive stress waves. This paper proposes a method of using piezoelectric transducers as strain gauges and acoustic emission (AE) sensors simultaneously. The signals received by piezoceramic transducers are decomposed into different frequency components for various analysis purposes. The low-frequency signals are used to measure strain, whereas the high-frequency signals are used as acoustic emission signal associated with local damage. The b-value theory is used to process the AE signal in piezoceramic transducers. The proposed method was applied in the bending failure experiments of two reinforced concrete beams to verify its feasibility. The results showed that the extracted low-frequency signals from the piezoceramic transducers had good agreement with that from the strain gauge, and the processed high-frequency signal from piezoceramic transducers as AE could indicate the local damage to concrete. The experimental results verified the feasibly of structural health monitoring using piezoceramic transducers as strain gauges and AE sensors simultaneously, which can advance their application in civil engineering.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.8
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• pp.757-766
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• 2004

This paper focuses on the formulation and validation of an automatic strategy to select the optimal location and direction of strain gauges for the measurement of the modal response. These locations and directions are important to render the strain measurements as robust as possible when a random mispositioning of the gauges and gauge failures are expected. The approach relies on the evaluation of the signal-to-noise ratios of the gauge measurements from strain data of finite element. The multi-step optimization strategy including genetic algorithm is used to find the strain gauge locations-directions that maximize the smallest modal strain signal-to-noise ratio in the absence of gauge failure or its expected value when gauge failure is possible. A flat Plate is used to prove the applicability of the proposed methodology and to demonstrate the effects of the essential parameters of the problem such as the mispositioning level, the probability of gauge failure, and the number of gauges.

• Journal of Industrial Technology
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• v.23 no.A
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• pp.165-173
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• 2003

The purpose of this paper is to analysis of initial behavior of concrete pavement with initial measurement strain gauge for concrete pavement at field, and to investigate the field test results for field applicability testing. The early-age behaviors of concrete pavement slabs were measured using the strain gauges. From the slab depths and positions, the outputs from each gauges were recorded at initial curing period. The initial measurement of concrete pavement and check of crack at the joint were performed, the results could be summarized as follows. From the results of concrete strength, compressive strength and flexural strength were showed $271kgf/cm^2$, $43kgf/cm^2$ respectively. From the tests of early-age strain measurement, it was found that the strain varied at the maximum value of $150{\mu}{\varepsilon}$ and early behavior of concrete slab was showed a tensile strain. However, for long-term was showed a compressive strain due to dry-shrinkage.

• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.96-102
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• 2006

Because of the increasing need to use clayey soil as the backfill in reinforced soil structures and embankment material, nonwoven geotextiles with the drain capability have been receiving much attention. However, there are few studies of the deformation behavior of nonwoven geotextiles at geosynthetics reinforced soil structures in the field because the nonwoven geotextile, which has low tensile stiffness and higher deformability than geogrids and woven geotextiles, is difficult to measure its deformation by strain gauges and to prevent the water from infiltrating. This study proposes a new, more convenient method to measure the deformation behaviour of nonwoven geotextile by using a strain gauge; and examines the availability of the method by conducting laboratory tests and by applying it on two geosynthetics reinforced soil (GRS) walls in the field. A wide-width tensile test conducted under confining pressure of 7kPa showed that the local deformation of nonwoven geotextile measured with strain gauges has a similar pattern to the total deformation measured with LVDT. In the field GRS walls, nonwoven geotextile showed a larger deformation range than the woven geotextile and geogrid; however, the deformation patterns of these three reinforcement materials were similar. The function of strain gauges attached to nonwoven geotextile in the walls works normally for 16 months. Therefore, the method proposed in this study for measuring nonwoven geotextile deformation by using a strain gauge proved useful.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.1 s.94
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• pp.3-11
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• 2005

For monitoring of the civil and building structure, optical fiber sensors are very convenient. The fiber sensors are very small and do not disturb the structural properties. They also have several merits such as electro-magnetic immunity, long signal transmission, good accuracy and multiplexibility in one sensor line. Strain measurement technologies with fiber optic sensors have been investigated as a part of smart structure. In this paper, we investigated the possibilities of fiber optic sensor application to the monitoring of beam-column joints of structures. We expect that the fiber optic sensors replace electrical strain gauges. The commercial electric strain gauges show good stability and dominate the strain measurement market. However, they lack durability and long term stability for continuous monitoring of the structures. In order to apply the strain gauges, we only have to attach them to the surfaces of the structures. In this paper, we investigate the possibility of using fiber optic Bragg grating sensors to joint structure. The sensors show nice response to the structural behavior of the joint.