• Proceedings of the Korean Society of Precision Engineering Conference
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• 1994.04b
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• pp.449-453
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• 1994

공작기계의 가공정밀도는 공구와 공작물간의 상대변위 크기로서 평가되는데, 이 상대변위는 가공중에 발생 하는 절삭력이 공구-척-주축-기계구조물-안내면-가공테이블-공작물로 이어지는 하중전달 폐곡선을 흐르면서 경로상의 정적, 동적 취약부의 주된 영향을 받아 생기거나 각 요소부품의 변형이 누적되어 생겨난다. 본 연구에서는 주축의 취약부를 규명하기 위하여 정적으로는 정적 처짐곡선을 이용하고, 동적으로는 진동모우드의 굽힘곡선을 이용하여 주축선단의 처짐에 가장 영향을 많이주는 부위를 파악하였다. 취약부의 개선방법으로는 주축지름을 변화시켜 주축선단 근처에서 굽힘이 집중되지 않도록 유도하였다. 그리고 구조개선의 효과를 확인 하기 위해서 기존 주축시스템과 개선 주축시스템의 정적, 동적 특성변화를 비교하였다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.5 no.4
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• pp.266-273
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• 1981

갑자기 작용하는 외압을 받는 직교이방성원통쉘의 동적좌굴을 해석하였다. Donnell-Karnam 형의 비선형방정식을 유도하였으며 쉘의 초기불완전성도 고려하였다. Galerkin의 방법을 사용하여 운동방정식을 구하고 Runge-Kutta 수직해법으로 비선형방정식을 풀었다. 쉘의 직교이방성특성이 처짐-하중 관계식의 비선형성에 미치는 영향을 검토하였으며 동적산출하중의 판별법을 정의하였다. 본 연구의 결과, 직교이방성원통쉘은 쉘의 초기불완전성에 그리 민감하지 않음을 보여주었다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1994.04a
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• pp.100-105
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• 1994

본 연구에서는 변속기 중립상태에서 클러치 설계 인자인 비틀림 스프링과 건마찰에 의해서 클러치에 나타나는 히스테리시스, 그리고 클러치 디스크의 정적처짐을 발생시키는 드래그토크(drag torque)가 클러치의 동적인 거동과 기어래틀에 미치는 영향을 분석하고자 한다.

• Magazine of the Korea Concrete Institute
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• v.7 no.6
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• pp.233-241
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• 1995

In this thesis, the fatigue tests were performed on a series of R /C beams repaired with co& crete-lmlyrner composites to investigate the fatigue bahavior. The three point loading system is used in the fatigue tests. In these tests, relations between the repeated loading cycles and mid-span deflections, number of repeated loading cycles when repaired beams were fractured, the bonding performance of repair materials were observed. On this basis, the mid-span deflections, the crack growth and failure mode of repaired R /C beams were studied. A S-N curve was drawn to present the fatigue strength of repaired beams. From the test results, it was shown that behavior of R /C beams repaired with polymer-cement series were very sirnillar to control beam about bonding performance, mid-span deflections and fatigue strength according to S-N curve drawn by the regression anlysis on the fatigue test results.

• Journal of the Korea institute for structural maintenance and inspection
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• v.28 no.2
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• pp.35-42
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• 2024

This study evaluated the buildability and mechanical properties of 3DP concrete printed in air and underwater environments. Buildability was evaluated by green strength test on fresh concrete and height and deflection immediately and 1 hour after printing. The green compressive strength of the concrete was 5.0 kPa after 30 minutes and 7.9 kPa after 3 hours, an increase of 1.6 times the initial strength. The total height of the laminated parts met the design height regardless of the printing environment. The amount of deflection in air and under water 1 hour after printing was 1 mm and 0.2 mm, respectively, indicating a small amount of deflection under water. The apparent density of the sample appeared in the order of A-M > A-P > UW-P. This is believed to be because a large amount of air is mixed into the concrete during the printing process, and water infiltrates during the underwater printing process. The compressive strength ratio of UW-P/A-P was 0.86 at 1 day, but the compressive strength of the underwater printed concrete was high from 7 days.

• Journal of the Korean Geosynthetics Society
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• v.11 no.3
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• pp.27-35
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• 2012

In this paper, the frost heaving and thawing characteristics of flexible pavement structure were evaluated in the large scale freezer which have a specification of temperature range $-20^{\circ}C{\sim}10^{\circ}C$ and $3.2m(L){\times}3.2m(B){\times}2.4m(H)$ in size. The insulated steel box with the size of $0.9m(L){\times}0.9m(B){\times}0.9m(H)$ was used to simulate actual pavement road structure. The variation of temperature, frost heave amount and frost heave pressure were measured through the instrument of TDS-602 data logger. LFWD (light falling weight deflectometer) was used to determine the change of deflection due to the frost heaving and thawing. Furthermore, the influence of aggregate layer to the freezing of the subgrade soil was studied to verify the function and effectiveness of the anti-freezing layer.

• Journal of the Korean Society of Hazard Mitigation
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• v.10 no.2
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• pp.15-21
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• 2010

Structural analysis used to evaluate the load carrying capacity of a bridge should implement behavioral characteristics similar to the actual behaviors of the structure through loading tests, but it is not feasible in many cases due to the behavioral characteristics of points, inadequate modeling method in structural analysis, errors in loading tests, changes in strength and rigidity resulting from cross-sectional damage, etc. This problem can be more serious if bridge bearings have been damaged or were not installed and, consequently, the bearings do not function properly. This study produced results similar to actual behaviors using a structural analysis model built with support moment derived from the difference $\Delta{\delta}$ between measured deflection obtained by confining the cantilever segment of a solid beam and calculated deflection under a unrestrained condition. When the load carrying capacity of a bridge in operation was evaluated in consideration of the confinement condition of supports, the result was 15~19% lower than load carrying capacity calculated by the existing method.

• Journal of the Earthquake Engineering Society of Korea
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• v.15 no.3
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• pp.1-9
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• 2011

The purpose of this study is to examine the dynamic characteristics of low, medium and high speed Maglev trains and guideways through dynamic interaction analysis. The coupled dynamic equations of motion for a vehicle of 10-dof and the associated guideway girders are developed by superposing vibration modes of the girder itself. The controller used in the UTM-01 Maglev vehicle is adopted to control the air gap between the bogie and guideway in this study. The effect of roughness, the guideway deflection-ratio and vehicle speed on the dynamic response of the maglev vehicle and guideway are then investigated using the 4th Runge-Kutta method. From the numerical simulation, it is found that the air gap increases with an increase of vehicle speed and the roughness condition. In particular, the dynamic magnification factor of the guideway girder is small at low and medium speeds, but the factor is noticeable at super-high speeds.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.2
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• pp.175-182
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• 2020

The application of epoxy coated reinforcements is increased as a means to prevent a corrosion of reinforcements embedded in reinforced concrete structures, However, epoxy coating may reduce the bond capacity between concrete and reinforcement, which results a longer development length and lap splice length. This paper aims to the possibility of modification in lap splice length from reduction of basic development length which was confirmed using a direct pull out test. Total 36 beam specimens were tested to compare the lap splice properties of normal and epoxy coated reinforcements with beam-end test for various lap lengths and diameters of reinforcements. According to the results on failure modes, deformations, and crack widths of this experiments, the modification factor of 1.2 should be used, though the direct bond capacity is assured through direct pull out test.

• Composites Research
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• v.34 no.6
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• pp.394-399
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• 2021

Piecewise Integrated Composite (PIC) is a new concept to design composite structures of multiple stacking angles both for in-plane direction and through the thickness direction in order to improve stiffness and strength. In the present study, PIC beam was suggested based on 3D training data instead of 2D data, which did offer a limited behavior of beam characteristics, with enhancing the stiffness accompanied by reduced tip deformation. Generally training data were observed from the designated reference finite elements, and preliminary FE analysis was conducted with respect to regularly distributed reference elements. Also triaxiality values for each element were obtained in order to categorize the loading state, i.e. tensile, compressive or shear. The main FE analysis was conducted to predict the mechanical characteristics of the PIC beam.