• Smart Structures and Systems
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• 제5권4호
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• pp.381-395
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• 2009

The paper presents a case study in which the structural condition assessment of the East Bay bridge in Gibsonton, Florida is evaluated with the help of remote health monitoring techniques. The bridge is a four-span, continuous, deck-type reinforced concrete structure supported on prestressed pile bents, and is instrumented with smart Fiber Optic Sensors. The sensors used for remote health monitoring are the newly emerged Fabry-Perot (FP), and are both surface-mounted and embedded in the deck. The sensing system can be accessed remotely through fast Digital Subscriber Lines (DSL), which permits the evaluation of the bridge behavior under live traffic loads. The bridge was open to traffic since March 2005, and the collected structural data have been continuously analyzed since. The data revealed an increase in strain readings, which suggests a progression in damage. Recent visual observations also indicated the presence of longitudinal cracks along the bridge length. After the formation of these cracks, the sensors readings were analyzed and used to extrapolate the values of the maximum stresses at the crack location. The data obtained were also compared to initial design values of the bridge under factored gravity and live loads. The study showed that the proposed structural health monitoring technique proved to provide an efficient mean for condition assessment of bridge structures providing it is implemented and analyzed with care.

• 대한조선학회지
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• 제3권1호
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• pp.33-45
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• 1966

The effect of thermal stress on a ship's hull is not considered to be serious by most naval architects. Frequently, however, cracking of hulls has been reported which occurred at sea while there were no external forces except the heat from the sun. Detailed investigations have been made of these reports and it has been reliably determined that the damage was initiated by solar heating. The author is not interested in all steel ship or in the applicability and validity of the formular itself, as it has already been proven by the experiments such as S.S. Boulder Victory. The author therefore proceeds directly to calculate the stress distribution on he hull and superstructure of the prototype model ship. These calculations are based on the experimental nonsymetrical temperature gradient data taken earlier on the Boulder Victory. The calculations were made principally to determine the extent of stresses which occurred on an all-steel ship in one case and secondly, those that occurred on a ship with a steel hull and an aluminum superstructure. From the calculations, the author expected the stress distribution of the two case would show distinctly different aspects, but the acquired results were very similar. Generally, at the point of junction of the steel hull and aluminum superstructure sharp peak stresses appeared. At the juncture of the superstructure and the main deck the ship with the aluminum superstructure registered almost 1000 psi more stress than did the ship with the all-steel construction. In the view of these findings, the author recommends to ship designers that pay particular attention to the point of junction of steel and aluminum plate. The author has proven that it is extremely important that a greater safety factor be used at the aluminum-steel junction point than at any other point. Although thermal effects cause high juncture-point stresses in all-steel ships, they are not nearly as critical as in ship constructed of two or more metals.

• 대한조선학회논문집
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• 제47권6호
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• pp.821-830
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• 2010

Deck plates and hatch coming of large container carrier and offshore structures are joined by ultra-thick plates whose thickness is more than 60mm. Traditionally FCAW has been used to join the thick plates in butt joint. However, FCAW has been replaced with EGW since the welding efficiency of EGW is higher than that of FCAW. Tandem EGW using two electrodes has been applied to vertical position welding by several shipyards. EGW requires one or two layers of bead whereas FCAW requires more than 20 layers of weld bead in thick welding. However, high welding residual stresses are generated by EGW since it uses higher heat input than FCAW. In the present study, a finite element model is suggested to predict the residual stresses induced by the tandem EGW. Butt specimen of EH40 TMCP shipbuilding steel plates vertical welding was modeled by a three-dimensional model. Residual stresses were measured by X-ray diffraction method and to verify the numerical result. The results show a good agreement with experimental result.

• 한국터널지하공간학회 논문집
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• 제22권4호
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• pp.435-450
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• 2020

복층터널의 분기구간은 터널 형상이 모자 모양의 대단면 구간인 '분기 전 확폭구간'과 본선과 분기터널 간 이격이 생기는 '분기 후 구간'으로 나눌 수 있으며, 분기 전 확폭구간의 터널 단면이 분기 후 구간의 단면에 비해 매우 크기 때문에 이러한 차이에 따른 굴착 영향이 분기구의 전체적인 굴착 안정성 검토 시 고려되어야 한다. 본 연구에서는 암반에서 시공되는 NATM 방식의 2차로 대심도(40 m) 본선 복층터널에서 1차로 단층터널로 분기가 되는 조건을 대상으로 3차원 유한요소해석을 통해 분기 전 확폭구간 굴착(선행굴착) 시 굴착공법과 벤치길이 변화에 따라 선행굴착이 분기 후 구간의 굴착 안정성에 미치는 영향을 검토하였다. 그 결과, 굴착공법과 벤치길이 변화에 따른 차이는 상대적으로 작은 편이었으나, 2차원 수치해석에 의한 선행굴착을 고려하지 않은 경우와 강도응력비 비교를 통해 선행굴착이 분기 후 구간의 굴착 안정성에 영향을 미칠 정도로 큰 응력의 변화를 유발함을 확인하였다.

• 산업기술연구
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• 제24권A호
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• pp.165-171
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• 2004

Latex modification of concrete provides the material with higher flexural strength, as well as high bond strength and reduced water permeability. However, If the thermal expansion properties of overlay concrete (latex-modified concretes) are big different from that of substrate (ordinary portland cement concrete), these would cause a big interfacial stresses and result in premature failure. Therefore, the purposes of this study were to investigate thermal expansion characteristics of latex-modified concrete with cement types. The result of thermal expansion showed the coefficient of thermal expansion of concretes increased with latex inclusion. The coefficient of thermal expansion of RSLMC was a little smaller than that of LMC, which might be due to the finer cement grain, compacter internal, and stiffer properties of concrete. However, the coefficients of LMC and RSLMC were quite similar to that of ordinary cement concrete. Thus, this would not cause an interfacial stresses and will enable to ensure long-term performance of concrete bridge deck overlays.

• 한국CDE학회논문집
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• 제9권2호
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• pp.112-121
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• 2004

As customers demands are rapidly changing, a product life cycle is getting shorter and a product model is forced to be changed frequently. An ejecting design system becomes more important for high productivity to eject a product in high temperature without any damage. For example, an ejector pin that is a key component of the system can cause high local stresses and strains in the molding at the time of ejection. The number, the size, and the location of pins are important to make a smooth ejection. Therefore we propose an analytical approach with the aid of designer’s experience to calculate a total release force and pressure distribution so that the number, the size, and the location of pins can be easily determined. As a part of the result, the design system is built by Intent! with AutoCAD 2000 and a video player deck example is presented to verify the approach.

• 한국자동차공학회논문집
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• 제5권3호
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• pp.147-158
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• 1997

This paper presents the analysis technique and procedure of main engine components-cylinder block, cylinder liners, gasket and cylinder head-using the finite element method, which aims to assess mainly the potential of lower oil consumption in a view point of engine design and to decide subsequently the accuracy of engine design which was done. The F.E. model of an engine section consisting of one whole cylinder and two adjacent half cylinders is used, whereby the crankcase is cut off at the block bottom deck. By means of a 3-dimensional F.E. model-including cylinder block, liners, gasket, cylinder head, bolts and valve seat rings as separate parts a linear analysis of deformations and stresses was performed for three different loading conditions;assembly, thermal and gas loads. For the analysis of thermal boundary conditions also the temperature field had to be evaluated in a subsequent step.

• 대한조선학회논문집
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• 제40권2호
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• pp.63-68
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• 2003

With the trend of large-sized ship in Korea, recently several hundreds of thousands of U-bolts for a year have been used as a pipe fastener In this paper, we have evaluated the strength for present U-bolt structure by pipe supporting conditions(deck, ceiling and wall mounting type) For this purpose, the equivalent and bending stresses have been calculated by linear elastic analysis using the finite element program ABAQUS. At the same time, a variety of load conditions such as design pressure, weight effect and acceleration are also considered.

• 한국안전학회지
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• 제18권2호
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• pp.132-138
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• 2003

고속철도교량에서 장대레일의 사용은 연결부 근처에서 레일과 교량상판사이의 비선형 거동으로 인하여 부가적인 응력을 유발한다. 고속철도 교량의 지진응답해석에서, 구조물응답은 지반운동특성에 매우 영향을 많이 받으므로, 지반운동의 위치에 따른 변화가 구조물의 응답에 영향을 미치게 되고, 그 결과는 레일에 응력을 유발하게 된다. 또한 고속철도에서 사용지진 수준의 지진발생 시에 열차의 긴 제동거리가 필요하므로 열차의 안전한 정지를 확보하는 것이 요구된다. 이러한 관점에서 장대레일에 의해 부가적으로 발생하는 응력, 지반운동의 공간변화에 대한 구조물 응답의 영향, 그리고 안전하게 정지하기 위해 필요한 열차의 제동거리 등의 사항이 레일의 응력해석에 고려될 필요가 있다. 본 논문에서는 지진하중을 받는 고속철도교량의 장대레일 응력해석을 위하여 제동하중, 지반운동의 공간적 변화, 그리고 레일의 재료 비선형을 고려한 시간영역에서의 비선형 동적해석방법을 개발하고 적용하였다. 제시된 방법을 한국고속철도의 특정부지에 적용하여 지반운동의 공간변화에 따른 응답의 타당성을 보였다.

• Journal of Welding and Joining
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• 제15권4호
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• pp.143-153
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• 1997

In this study, bending test was performed on the real-scale, built-up beam test model fabricated by the $CO_2$ arc spot welding to evaluate the applicability of the welding method to the production of the stiffened plate in car-carrying ship. The built-up beam models which were fixed at both ends in longitudinal direction or simply supported to the rigid foundation, depending on the restraint condition of the corresponding car decks considered, were subjected to simulated design vehicle loads or concentrated point loads. During the test, the central deflection and the longitudinal bending stresses were measured from several points on the longitudinal flange face to predict the section properties of the built-up beams. The longitudinal bending stress on each spot weld were also measured to calculate the average horizontal shear force subjected to spot welds. Test results revealed that the shear strength of spot welds with their current weld nugget size and welding pitch was adequate enough to withstand the horizontal shear forces under the design vehicle loads. Although the built-up beam fabricated by the arc spot welding was a discontinuous beam, its mechanical behavior was well explained by the continuous beam theory using the effective breadth of plate. Based on test results, the criterion for the size of spot weld of which the average shear stress might meet the allowable stress requirement of AWS Code could be established.