• 한국지반공학회논문집
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• 제21권7호
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• pp.73-80
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• 2005

도로기초에서 입상재료의 응력의존 특성을 반영하면 응력의존 탄성계수와 응력 의존 포와송 비 모두를 동시에 고려할 수 있다. 이 방식은 기존 연속체 역학에 기초한 해석 방식과는 달리 층모형 내에서 인장력의 발생 대신 압축력의 구현이 가능하여 재료의 강성과 연성에 대한 거동을 동시에 반영하여 입상재료층의 변형 예측에 많은 영향을 주고 있다 따라서 본 논문에서는 도로기초를 대상으로 제안된 응력의존 및 변형 모형을 대상으로 유한요소법에 의한 도로기초 층변형 예측 알고리즘을 제안하였고 층변형 예측시 응력의존의 고려에 따른 영향을 분석하였다.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2015년도 춘계 학술논문 발표대회
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• pp.63-64
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• 2015

This study has analyzed mechanical and dry shrinkage properties according to the recycled coarse aggregate by nominal strength actually being widely used at the Remicon companies for the purpose of qualitative improvement of concrete, practical use and examination at various strengths. As a result, although the modulus of elasticity showed a tendency of getting decreased as the replacement ratio of recycled coarse aggregate has increased, the difference was insignificant while the compressive strength showed a tendency of about 3MPa increase in the recycled coarse aggregate replacement ratio of 30% compared to the ratio of 0%. In case of the dry shrinkage length variation ratio, the recycled coarse aggregate replacement ratio of 30% showed a tendency of about 20% shrinkage reduction compared to the ratio of 0%.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2009년도 추계 학술논문 발표대회
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• pp.81-85
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• 2009

In the recent years, the high strength concrete has increasingly been used according to extending market of tall buildings. However, Ministry of Land, transport and Maritime Affairs was established by law with an alternative plan after June 2008 because of the weakness of high strength concrete accompanied spalling phenomena in fire. The mix design of concrete has to properly meet standards which are the spalling resistance of concrete and limited temperature of steel reinforcement. The fire proof concrete mixed fiber has widely been used to meet spalling safety on the many construction sites, the most researches about the fire proof concrete mixed fiber had being carried out focused on fire resistance, compressive strength and cast in place of concrete. But the most important thing is column shortening used the fire proof concrete within the vertical members. In this paper, the fire proof concrete filled spalling safety standards was experimented by required material when the column shortening is revised between normal concrete and fire proof concrete mixed fiber and then the results have done a comparative analysis. Also, The paper aimed to indicate a basic data for revision of column shortening of fire proof concrete.

• Structural Engineering and Mechanics
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• 제28권3호
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• pp.295-316
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• 2008

In the present paper a mechanical model to predict the compressive response of high strength short concrete columns with square cross-section confined by transverse steel is presented. The model allows one to estimate the equivalent confinement pressures exercised by transverse steel during the loading process taking into account of the interaction of the stirrups with the inner core both in the plane of the stirrups and in the space between two successive stirrups. The lateral pressure distributions at hoop levels are obtained by using a simple model of elastic beam on elastic medium simulating the interaction between stirrups and concrete core, including yielding of steel stirrups and damage of concrete core by means of the variation in the elastic modulus and in the Poisson's coefficient. Complete stress-strain curves in compression of confined concrete core are obtained considering the variation of the axial forces in the leg of the stirrup during the loading process. The model was compared with some others presented in the literature and it was validated on the basis of the existing experimental data. Finally, it was shown that the model allows one to include the main parameters governing the confinement problems of high strength concrete members such as: - the strength of plain concrete and its brittleness; - the diameter, the pitch and the yielding stress of the stirrups; - the diameter and the yielding stress of longitudinal bars; - the side of the member, etc.

• Structural Engineering and Mechanics
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• 제56권3호
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• pp.473-490
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• 2015

This paper presents the analysis of intermediate crack-induced (IC) debonding failure loads for reinforced concrete (RC) beams strengthened with adhesively-bonded fiber-reinforced polymer (FRP) plates or sheets. The analysis consists of the energy release and simple ACI methods. In the energy release method, a fracture criterion is employed to predict the debonding loads. The interfacial fracture energy that indicates the resistance to debonding is related to the bond-slip relationships obtained from the shear test of FRP-to-concrete bonded joints. The section analysis that considers the effect of concrete's tension stiffening is employed to develop the moment-curvature relationships of the FRP-strengthened sections. In the ACI method, the onset of debonding is assumed when the FRP strain reaches the debonding strain limit. The tension stiffening effect is neglected in developing a moment-curvature relationship. For a comparison purpose, both methods are used to numerically investigate the effects of relevant parameters on the IC debonding failure loads. The results show that the debonding failure load generally increases as the concrete compressive strength, FRP reinforcement ratio, FRP elastic modulus and steel reinforcement ratio increase.

• Structural Engineering and Mechanics
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• 제31권4호
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• pp.371-382
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• 2009

The concrete plates are most widely used structural elements in the hulls of floating concrete structures such as concrete barges and pontoons, bridge decks, basement floors and liquid storage tanks. The study on the behavior of high-strength fiber reinforced concrete (HSFRC) plates was carried out to evaluate the performance of plates under in-plane and transverse loads. The plates were tested in simply supported along all the four edges and subjected to in-plane and traverse loads. In this experimental program, twenty four 150 mm diameter cylinders and twelve plate elements of size $600{\times}600{\times}30$ mm were prepared and tested. Water-to-cementitious materials ratios of 0.3 and 0.4 with 10% and 15% silica fume replacements were used in the concrete mixes. The fiber volume fractions, $V_f$ = 0%, 1% and 1.5% with an aspect ratio of 80 were used in this study. The HSFRC mixes had the concrete compressive strengths in the range of 52.5 to 70 MPa, flexural strengths ranging from 6.21 to 11.08 MPa and static modulus of elasticity ranging from 29.68 to 36.79 GPa. In this study, the behavior of HSFRC plate elements subjected to combined uniaxial in-plane and transverse loads was investigated.

• Nuclear Engineering and Technology
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• 제48권1호
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• pp.259-267
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• 2016

Most manufacturing processes, including welding, create residual stresses. Residual stresses can reduce material strength and cause fractures. For estimating the reliability and aging of a welded structure, residual stresses should be evaluated as precisely as possible. Optical techniques such as holographic interferometry, electronic speckle pattern interferometry (ESPI), Moire interferometry, and shearography are noncontact means of measuring residual stresses. Among optical techniques, ESPI is typically used as a nondestructive measurement technique of in-plane displacement, such as stress and strain, and out-of-plane displacement, such as vibration and bending. In this study, ESPI was used to measure the residual stress on the welded part of butt-welded American Society for Testing and Materials (ASTM) A36 specimens with $CO_2$ welding. Four types of specimens, base metal specimen (BSP), tensile specimen including welded part (TSP), compression specimen including welded part (CSP), and annealed tensile specimen including welded part (ATSP), were tested. BSP was used to obtain the elastic modulus of a base metal. TSP and CSP were used to compare residual stresses under tensile and compressive loading conditions. ATSP was used to confirm the effect of heat treatment. Residual stresses on the welded parts of specimens were obtained from the phase map images obtained by ESPI. The results confirmed that residual stresses of welded parts can be measured by ESPI.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 추계 학술발표회 논문집
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• pp.445-448
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• 2006

Mix design of C80A which is applied to the vertical members of The Burj Dubai Tower, the tallest building of the world, was performed so as to meet the requirements of rheological property, mechanical properties & construction sequences based on material analysis in Dubai, UAE. Experimental investigations were carried out to evaluate & optimize the quantities of total binders, the proportions of Micro Silica, Dune Sand & PFA, changes of S/a and the comparison of chemical admixture, etc. Approximately $65,000m^3$ of C80A concrete has been poured to the vertical members since 16-Apr-2006. In the actual application, it was showed that C80A has proper early strength achievement, excellent mechanical properties and satisfactory flowability & workability. The results of extensive site testing can be summarized that the average compressive strength at 28days is 98.8MPa, the average elastic modulus at 28days is 47.8GPa, the flow of concrete after pumping at the height of 250m (L72) was over 500mm.

• 지질공학
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• 제14권1호
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• pp.105-121
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• 2004

화강암은 국내에서 건축재, 공예 재료로서 사용되는 석재들 중 가장 큰 비중을 차지한다. 화강암은 구성광물, 광물의 함량 변화가 크기 때문에 이에 따라 물리적, 공학적 특성변화가 다양하다. 이 연구의 목적은 국내에서 화강암 석재가 가장 많이 생산되는 지역 중 하나인 남원지역의 화강암을 대상으로 암석기재학적 인 특성과 공학적인 특성사이의 상호 관련성을 규명하기 위한 것이다. 화강암의 구성광물의 함량비와 구성광물 각각의 입도를 측정하였으며 동일 시료에 대해 밀도, 흡수율, 공극율, 일축압축강도, 인장강도, 마모경도, P파 속도, 탄성계수, 포아송비 등의 물성 측정이 실시되었다. 화강암의 공학적 특성은 광물의 함량비 보다는 광물의 입도에 더 큰 영향을 받는 것으로 나타났다. 그러나 석영의 함량비도 화강암의 공학적 성질에 역시 영향을 주는 것으로 판단된다.

• 터널과지하공간
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• 제21권5호
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• pp.359-369
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• 2011

본 연구에서는 굴착 전 후에 채취한 암석시료들에 대해 물리적, 역학적 그리고 열적 물성을 조사하여, KAERI Underground Research Tunnel(KURT)의 건설로 인해 발생된 굴착손상영역(EDZ)을 정량적으로 평가하고자 하였다. 굴착손상영역에서 공극률은 약 140% 정도 증가하였고, 탄성파속도, 탄성계수, 그리고 일축압축강도는 각각 약 11, 37, 그리고 16% 정도 감소하였다. 또한 굴착손상영역에서의 열전도도는 약 20% 정도 감소하였다. 암석물성변화를 이용하여 KURT 굴착손상영역의 범위를 판단한 결과 약 1.1-2.4 m로 나타났다.