• Journal of Welding and Joining
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• 제20권3호
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• pp.84-90
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• 2002

The strength and the life of welded components are affected extensively by the residual stresses distributed around their weldments not only under static loads, but also fatigue loads. The residual stress can be superimposed with externally applied loads, so that unexpected deformations and failures of members will be occurred. These residual stresses are not kept constant, but relaxed or redistributed during in service. Under static loads the relaxation takes place when the external stress superimposed with the residual stress exceeds locally the yield stress of material used. It is shown that under fatigue loads the residual stress is considerably relieved by the first or flew cycle loading, and then gradually relaxed with increasing loading cycles. In this study the phenomenon and mechanism of the stress relaxation by mechanical means were investigated and a model to predict quantitatively the residual stress relaxation for the case of static and fatigue loading condition was proposed.

• 패션비즈니스
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• 제14권2호
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• pp.57-72
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• 2010

The purposes of the research were to find out the clothing construction factors of the mechanical industry working clothes by analyzing the working clothes supplied to 5 subject companies; and to suggest the optimized sewing conditions and the seam strength and elongation experimental data according to the clothing material and seam types implied to the working clothes collected. The fabric types and trimmings used for the mechanical manufacturing working clothes were Polyester/Cotton(65/35%), Polyester/Rayon(65/35%), Cotton(100%); and linings, interlining, various fastenings etc. 2 stitch types, i.e. lock and two-thread chain stitches were applied to the construction of the flat, lap felled, French, superimposed, lapped and bound seams for the seam strength and elongation experiment. The results derived from the experiment were as follows. (1) The seam strength results according to the seam types were high in the order of lap felled>lapped>flat, superimposed and French seams. (2) Considering the features of the seam construction, as the number of fabric layers at the seam line increased the seam strength also increased. (3) Apart from the highest seam strength from the experiment using the net lining with the main fabric, the seam construction consisting of two fabric layers with the interlining showed relatively high seam strength results. (4) The seam elongations according to the stitch types were high in the order of two-thread chain>lock stitches.

• 한국전문물리치료학회지
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• 제29권2호
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• pp.140-146
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• 2022

Background: The superimposed technique (ST) involves the application of electrical muscle stimulation (EMS) during voluntary muscle action. The physiological effects attributed to each stimulus may be accumulated by the ST. Although various EMS devices for the quadriceps muscle are being marketed to the general public, there is still a lack of research on whether ST training can provide significant advantages for improving quadriceps muscle strength or thickness compared with EMS alone. Objective: To compare the effects of eight weeks of ST and EMS on the thicknesses of the rectus femoris (RF) and vastus intermedius (VI) muscles and knee extension strength. Methods: Thirty healthy subjects were recruited and randomly assigned to either the ST or EMS groups. The participants underwent ST or EMS training for eight weeks. In all participants, the thicknesses of the RF and VI muscles were measured before and after the 8-week intervention by ultrasonography, and quadriceps muscle strength was measured using the Smart KEMA tension sensor (KOREATECH Co., Ltd.). Results: There were significant differences in the pre- and post-intervention thicknesses of the RF and VI muscles as well as the quadriceps muscle strength in both groups (p < 0.05). RF thickness was significantly greater in the ST group (F = 4.294, p = 0.048), but there was no significant difference in VI thickness (F = 0.234, p = 0.632) or knee extension strength (F = 0.775, p = 0.386). Conclusion: EMS can be used to improve quadriceps muscle strength and RF and VI muscle thickness, and ST can be used to improve RF thickness in the context of athletic training and fitness.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1995년도 가을 학술발표회 논문집
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• pp.215-218
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• 1995

This paper presents an experimental study on the strength and deformation of concrete-filled circular steel short columns. Six specimens of concrete-filled circular short columns were tested under concentric compressive load. For comparsion, three specimens of circular steel short columns were also loaded to failure. The ultimate strength, ductility, and confinement mechanism of columns were compared. In the comparison, the effect of witch-thickness ratio and concrete compressive strength on the behavior of colimns were examed. As a result, the axial load verse axial average strain relationship of concrete-filled circular steel columns was very stable, because of interactions between the concrete and steel, the strength are 13% and 30% larger than the strength extimated by simply superimposed method of the concrete and steel. The ratio of the circumferential to longitudinal strain increment, both measured on the steel suface, was 0.28 up to the longitudinal strain of 0.1%, increases from 0.3 to 0.8 between the strain of 0.1% to 0.3%, and 0.8 beyond the strain of 0.3%

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집A
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• pp.424-429
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• 2001

Residual stresses can be produced during manufacturing processes, eg. welding, machining and plastic working, and also in service. It can be superimposed with externally applied loads, so that unexpected deformations and failures of members will be occurred. Especially, the strength and the life of welded components are affected extensively by the residual stresses distributed around their weldments not only under static loads, but also fatigue loads. These residual stresses are not kept constant, but relaxed or redistributed during service. Under static loads the relaxation takes place when the residual stress superimposed with external stress exceeds locally the yield stress of material used. It is shown that under fatigue loads the residual stress is considerably relieved by the first or few cycle loading, and then gradually relaxed with increasing loading cycles. Although many investigations in this field have been carried out, the phenomenon and mechanism of the stress relaxation by mechanical means are still not clear, and there are few comprehensive models for predicting specific effects on the stress relaxation. In this study, the effects of applied static and fatigue loads on the residual stress relaxation were Investigated, and a model to predict quantitatively the residual stress relaxation was proposed.

• 한국지반환경공학회 논문집
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• 제19권12호
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• pp.5-14
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• 2018

최근 국내에 사용되고 있는 보강토옹벽 공법은 전면체의 재질, 보강재, 축조방법, 축조경사에 따라 수많은 종류가 제안되었으나 각 공법에 따른 설계방법이나 상세검토항목 등의 규정이 명확하지 않으며 집중호우에 따른 붕괴도 빈번하게 발생하고 있는 실정이다. 본 연구에서는 이러한 보강토옹벽의 설계에 있어서 좀 더 안정된 기술적 접근을 위해 설치높이별 단면을 가정하고 단일 강도의 보강재를 사용한 보강토옹벽의 인발파괴와 높이별 최적의 보강재 조합을 산정하고 산정된 각 단면에 대해서 보강길이비(L/H)에 따른 안전율 변화를 통하여 보강재의 최적 설계와 다단식 보강토옹벽의 최적 설계 그리고 보강재인 토목섬유의 재질에 따른 최적 길이비를 산정하여 제시하였다.

• Steel and Composite Structures
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• 제34권3호
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• pp.423-440
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• 2020

In the recent years, steel box girder bridges have been extensively used due to high bending stiffness, torsional rigidity, and rapid construction. Therefore, researches related to this girder bridge have been widely conducted. This paper investigates the effect of residual stresses and geometric imperfections on the load-carrying capacity of steel box girder bridges spanning 30 m and 50 m. A three - dimensional finite element model of the steel box girder with a closed section was developed and analyzed using ABAQUS software. Nonlinear inelastic analysis was used to capture the actual response of the girder bridge accurately. Based on the results of analyses, the superimposed mode of webs and flanges was recommended for considering the influence of initial geometric imperfections of the steel box model. In addition, 4% and 16% strength reduction rates on the load - carrying capacity of the perfect structural system were respectively recommended for the girders with compact and non-compact sections, whose designs satisfy the requirements specified in AASHTO LRFD standard. As a consequence, the research results would help designers eliminate the complexity in modeling residual stresses and geometric imperfections when designing the steel box girder bridge.

• 한국지반공학회지:지반
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• 제4권3호
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• pp.35-42
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• 1988

이방성과추밀점토의 3차원 강도특성을 조사하기 위하여 일연의 압밀비배수 입방기형삼축시험이 실시되었다. 현장에시 직접 채취된 자연시료가 사용되었으며, 공시체의 주응력축을 시초채취시의 직교 좌표축과 일치시켜 정팔면체면상의 3차원 성괴면이 충분히 얻어질 수 있도흑 충분한 회수의 시험을 실시하였다. 본 연구결과, 측정된 유효내부라찰각은 재료축방향에 따라 현저하게 차이를 보이고 있으나 동일한 정팔면체면상에 투영시킨 응력상태로 부터 구한 수정된 유효내부마찰각은 이방성을 거의 보이지 않았다. 따라서 등방체의 파양규준으로 제안된 Lade의 파장각잘은 업방성과맥밀점 토의 파괴규준으로도 충분한 실용성이 있음을 알 수 있었다. 또한 파양시의 변형율 증분벡터도 정팔면체면상의 파괴면에 직교성을 보였다.

• 콘크리트학회논문집
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• 제11권4호
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• pp.43-54
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• 1999

Shear tests are performed on four full-scale 12.5 m proto-type models, "least depth double tee," which are resulted from the optimization process. Domestic superimposed live load regulation, domestic material properties which is available to product. Korean building code requirements, construction environments and economy are considered as the main factors to establish the process. All of the specimens tested fully comply with the shear strength requirements as specified by ACI 318-95. The research has shown following results. 1) The development length requirement of ACI 318-95 does not seem a good predictor for the estimation of bond failure in a beam with the strands below the supports. 2) The load required for the first initial coner cracking in the dap end and first web shear cracking does not seem to have any relation with the dimension and shear strength of the section in the test beams. 3) The strand slip has a direct relationship with the web shear cracking. However, the coner cracking in the dap end does not give any help for the slip in anchorage. 4) Use of whole area for bearing steel at the bottom of dap end is desired for safe bearing pressure design in the precast prestressed double tee beams. 5) The deflection of beam influences directly on the amount of strand slip at the anchorage after initiation of it, and relationship between them are very linear.

• 콘크리트학회논문집
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• 제11권3호
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• pp.141-152
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• 1999

Precast prestressed double-tee slab may be designed by the PCI Design Handbook. It is based on the bridge construction and is required for reorganization for the use of buildings in the domestic construction environments. Much enhanced sections are developed from the reforming process on the determined design factors in the previous experimental works on double tees. Pre-determined shape, reinforcement detail, and 5000 psi concrete strength can not be expected as the best solution for the domestic construction requirements because large amount of use on that systems are anticipated. Flexural tests are performed on four full-scale 12.5m proto-type models, "least depth double tee", which are resulted from the optimization process. Domestic superimposed live load regulation, domestic material properties which is available to product, building design requirements and economy in construction are considered as the main factors to establish. the first two sections are double tee section for 1.2 ton/$\m^2$ market live load with straight and one-point depressed strands and the second two are for 0.6 ton/$\m^2$ parking live load with those strand types. All of the specimens tested fully comply with the flexural strength requirements as specified by ACI 318-95. However, the research has shown that following improved considerations are needed for better result in practice. The locations and method of connection for the lowest bottom mild bar, connection method between precast and cast-in-place concrete, and dap-end reinforcement are need to be improved.