• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.4
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• pp.305-312
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• 2007

Among many types of light rail transits (LRT), the rubber-tired automated guide-way transit (AGT) is prevalent in many countries due to its advantages such as good acceleration/deceleration performance, high climb capacity, and reduction of noise and vibration. However, AGT is generally powered by high-voltage electric power feeding system and it may cause electromagnetic interference (EMI) to measurement sensors. The fiber optic sensor system is free from EMI and has been successfully applied in many applications of civil engineering. Especially, fiber Bragg grating (FBG) sensors are the most widely used because of their excellent multiplexing capabilities. This paper investigates a prestressed concrete girder bridge in the Korean AGT test track using FBG based sensors to monitor the dynamic response at various vehicle speeds. The serviceability requirements provided in the specification are also compared against the measured results. The results show that the measured data from FBG based sensors are free from EMI though electric sensors are not, especially in the case of electric strain gauge. It is expected that the FBG sensing system can be effectively applied to the LRT railway bridges that suffered from EMI.

• Journal of the Korean Geotechnical Society
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• v.24 no.1
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• pp.81-89
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• 2008

The purpose of this study is to develop a new technique to quickly assess the quantitative stability of a tunnel by using measured displacement at the tunnel construction site. To achieve this purpose, in this study, a critical strain concept was introduced for the first time and applied to an assessment of a tunnel under construction. The new technique calculates numerically the strains of the surrounding ground by using displacements measured during tunnel excavation. The techniques considering the relative displacement, shotcrete, and anisotropic characteristics of ground were newly introduced after reinvestigating the existing analysis technique. In addition, an analysis module was developed based on the proposed analysis technique in this study, and the applicability of the developed module was verified. To verify the module, first of all, the calculated excavation displacements of a cylindrical tunnel by analytic method and commercial programs (Pentagon-3D, Flac-2D) were compared for the confirmation of applicability of commercial programs. Then, the calculated excavation displacements under the same initial condition, both with and without a shotcrete lining, by two commercial programs were compared. finally, we assess the load condition and material properties of in-situ ground by inputting tunnel excavation displacement, which was calculated by a commercial program, into the developed analysis module (FAST-Ver. 1.2, feedback Analysis System for Tunneling), and checked whether the assessed results conform to the originally assumed values.

• Journal of Aerospace System Engineering
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• v.16 no.1
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• pp.104-109
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• 2022

The bomb rack unit (BRU) installed inside the pylon serves to fix external attachments such as external fuel tank or external weapon, and also serves to separate external attachments in case of emergency. In particular, the load generated when the external attachment is separated from the BRU is called the punching load. In this study, we present the results of a structural static test performed to verify the structural integrity of the pylon under the BRU punching condition acting on it. In the structural static test report, we present the implementation method for the separation load of the external attachment and the test profile for the BRU punching load condition, and compared the error between the load input signal and the feed-back signal to determine the appropriateness of load control in each test. Furthermore, we compared the strain results obtained in the numerical analysis and structural test at the main positions of the specimen. As a result, it was shown that the load of the actuators were properly controlled within the allowable error range in each test, and the numerical analysis effectively predicted the test result. Finally, through structural static tests conducted by design limit load and design ultimate load, we verified that the aircraft pylon dealt with in this study has sufficient structural strength for external attachment separation condition.

• Journal of the Korean GEO-environmental Society
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• v.16 no.12
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• pp.23-35
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• 2015

Nonlinear soil behavior before failure under dynamic loading is often implemented in a numerical analysis code by a mathematical fitting function model with Masing's rule. However, the model may show different behavior with an experimental results obtained from laboratory test in damping ratio corresponding secant shear modulus for a certain shear strain rage. The difference may come from an unique soil characteristics which is unable to implement by using the existing mathematical fitting model. As of now, several fitting models have been suggested to overcome the difference between model and real soil behavior but consequence of the difference in dynamic analysis is not reviewed yet. In this paper, the effect of the difference on site response was examined through nonlinear response history analysis. The analysis was verified and calibrated with well defined dynamic geotechnical centrifuge test. Site response analyses were performed with three mathematical fitting function models and compared with the centrifuge test results in prototype scale. The errors on peak ground acceleration between analysis and experiment getting increased as increasing the intensity of the input motion. In practical point of view, the analysis results of accuracy with the fitting model is not significant in low to mid input motion intensity.

• Journal of the Korean Geotechnical Society
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• v.23 no.7
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• pp.65-76
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• 2007

Recently, there have been many construction projects on soft ground with growth of industry and various construction problems concerning soft soil behavior also have been reported. Especially, foundation piles of abutments and (or) buildings which were constructed on the soft ground have been suffering from a lot of stability problems of inordinary displacement due to lateral flow of soft ground. Although many researches for this phenomena have been carried out, it is still difficult to assess the mechanism of lateral flow on soft ground quantitatively. And reliable design method for judgement of lateral flow occurrence is not established yet. In this study, PNN (probabilistic neural network) and CNN (committee neural network) theories were applied for judgment of lateral flow occurrence based on eat data compiled from Korea and Japan. Predictions of PNN and CNN models for new data which were not used during model development are compared with those predicted by conventional empirical methods. It was found that the developed PNN and CNN models can predict more precise and reliable judgment of lateral flow occurrence than conventional empirical methods.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.1C
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• pp.1-8
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• 2008

Recently, there have been many construction projects on soft ground with growth of industry and economy. Therefore foundation piles of abutments and(or) buildings had been suffering from a lot of stability problems of inordinary displacement due to lateral flow of soft ground. Although many researches about lateral flow have been carried out, it is still difficult to assess the mechanism of lateral flow in soft ground quantitatively. And reasonable design method for judgement of lateral flow occurrence in soft ground is not established yet. In this study, six PNN (Probabilistic Neural Network) models were developed according to input variables and database compiled from Korea and Japan for the judgment of lateral flow occurrence. PNN models were compared with present empirical methods. It was found that the developed PNN models can give more precise and reliable judgment of lateral flow occurrence than empirical methods.

• The korean journal of orthodontics
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• v.30 no.2 s.79
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• pp.159-174
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• 2000

Many treatment approaches of Cl III malocclusion have been introduced and the choice of treatment should be a function of the individual problem, not of the clinician(personal preference, experience and success rate of the operator). Therefore a function of the individual problem should be analysed exactly Much has been written in the orthodontic literature concerning the nature of Cl III malocclusion. It has been reported by many investigators that a Cl III malocclusion occurs in a variety of skeletal and dental configurations by differences of race and age. Lateral cephalometric radiographs of 125 individuals were studied for the presence and distibution of four horizontal components and one vortical component in a manner similar to McNamara. The results were as follows : 1. Cl III malocclusion is not a single clinical entity. It can result from numerous combinations of skeletal and dental components. 2. Maxillary skeletal retrusion was the most common single charateristic of the Cl III sample. 3. Only a small percentage of the cases in this study exhibited maxillary dentoalveolar protrusion. 4. Only a small percentage of the cases in this study exhibited mandibular dentoalveolar retrusion. 5. Mandible was usually well-positioned, but a wide variation was observed. 6. A large percentage of the cases in this study exhibited excessive vertical development. Thus, it appears that in designing the ideal treatment regime, those approaches which might restrict vertical development and promote maxillary horizontal growth could be more appropriate in many cases.

• The korean journal of orthodontics
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• v.33 no.2 s.97
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• pp.121-130
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• 2003

The purpose of this study was to evaluate the possibile clinical application of electroplating to increase diameter of an orthodontic wire, through examining the change of physical properties. The diameter of stainless steel orthodontic wire was increased from 0.016 inch to 0.018 inch by electroplating in a bath of nickel sulfate 100g/L, nickel chloride 60g/L, boric acid 30g/L, and sodium chloride 50g/L, under the conditions of 1.7V, $25\~29^{\circ}C\;and\;3.1\~3.3pH$. During the electroplating, the rate of diameter increase was measured every minute. To investigate uniformity, the diameter was measured at three different locations of each wire specimen aster electroplating. An X-ray diffraction test was performed to analyze the nature of the electroplated metal. Following heat treatment to improve adhesion between the wire and electroplated metal, a three-point bending test was conducted to compare stiffness, field strength, and ultimate strength among four wire groups; 0.016 inch, electroplated 016, electroplated and heat-treated 016, and 0.018 inch wires. Through the comparison of each wire group, following results were obtained. 1. In the load-deflection graph, the curve of the electroplated group was Placed between that of the 0.016 inch group and the 0.018 inch group, and the owe was closer to the 0.018 inch group by heat treatment. 2. In the electroplated and heat-treated 016 wire group, the values of stiffness, yield strength and ultimate strength showed higher tendency than in the original 0.016 Inch group. Stiffness and ultimate strength showed statistically significant differences between two groups. 3. Stiffness, yield strength, and ultimate strength of electroplated wire presented lower values than those of 0.018 inch wire group. 4. Stiffness, yield strength, and ultimate strength of electroplated and heat-treated wire showed higher tendency than those of electroplated wire group, and ultimate strength showed statistically significant difference between two groups. 5. After electroplating, the difference in diameter between the three locations was within $0.1\~0.3\%$ variation, and showed no statistical significance.

• Journal of the Korean Geotechnical Society
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• v.21 no.4
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• pp.65-70
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• 2005

Many case histories of re-liquefaction phenomena seem to support the idea that sand deposits, if they once have been liquefied, could be reliquefied again by a subsequent earthquake even though the earthquake is smaller than the previous one. The magnitude of the strains induced in the initial liquefaction has a significant influence on the resistance of the sample to re-liquefaction. The deposits undergoing liquefaction experience large shear strain during liquefaction. And this previous strain changes the microstructure into highly anisotropic structure such as columnlike structure and connected voids. This type of anisotropy is so unstable that it can reduce re-liquefaction resistance. It is blown that the extent of anisotropic structural change depends on the gradation characteristics of ground. The purpose of this study is to estimate the correlation between the gradation characteristics of the sand and the ratio of re-liquefaction resistance to liquefaction resistance. In this study, 1-g shaking table tests were carried out on five different kinds of sands. During the tests the values of excess pore pressure at various depths and surface settlements were measured. Re-liquefaction resistances were not affected by the initial void ratio and the effective confining pressures, and the deposits of all test sands which had once been liquefied were reliquefied in the cyclic loading number below 1 to 1.5. The ratio of re-liquefaction resistance to liquefaction resistance linearly decreased as $D_{10}/C_u$ increased, and was constant as about 0.2 above the value of $D_{10}/C_u$, 0.15 mm.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.37 no.1
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• pp.67-76
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• 2024

In this paper, we present a DIP-MLS testing method that combines digital image processing with a rigid body-based MLS differencing approach to measure mechanical variables and analyze the impact of target location and image resolution. This method assesses the displacement of the target attached to the sample through digital image processing and allocates this displacement to the node displacement of the MLS differencing method, which solely employs nodes to calculate mechanical variables such as stress and strain of the studied object. We propose an effective method to measure the displacement of the target's center of gravity using digital image processing. The calculation of mechanical variables through the MLS differencing method, incorporating image-based target displacement, facilitates easy computation of mechanical variables at arbitrary positions without constraints from meshes or grids. This is achieved by acquiring the accurate displacement history of the test specimen and utilizing the displacement of tracking points with low rigidity. The developed testing method was validated by comparing the measurement results of the sensor with those of the DIP-MLS testing method in a three-point bending test of a rubber beam. Additionally, numerical analysis results simulated only by the MLS differencing method were compared, confirming that the developed method accurately reproduces the actual test and shows good agreement with numerical analysis results before significant deformation. Furthermore, we analyzed the effects of boundary points by applying 46 tracking points, including corner points, to the DIP-MLS testing method. This was compared with using only the internal points of the target, determining the optimal image resolution for this testing method. Through this, we demonstrated that the developed method efficiently addresses the limitations of direct experiments or existing mesh-based simulations. It also suggests that digitalization of the experimental-simulation process is achievable to a considerable extent.