• Proceedings of the Korea Concrete Institute Conference
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• 1994.10a
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• pp.187-193
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• 1994

일반 콘크리트 (설계강도 $\sigma_{28}=210 kg/\textrm{cm}^2$)에 산업폐기물인 Fly Ash를 혼합하고 기포재 (Air Entrainment Agent) 첨가에 따른 Fly Ash-Concrete의 물성 변화를 시험하였다. Fly Ash-Concrete의 slump를 6, 8, 10cm로 고정시킨후, 각각의 slump 반죽상태에다 기포재, Neopor-400을 25,000cc/$\textrm{m}^3$, 50,000cc/$\textrm{m}^3$, 75,000cc/$\textrm{m}^3$으로 증가시켰다. 이때 기포재 증가에 따른 공기량 변화와 압축강도 $(\sigma_7 과 \sigma_{28})$ 를 측정하였다. 또한 기포재를 첨가한후, 60분과 90분까지 방치하고, 60분후와 90분후의 공기량과 압축강도 $(\sigma_7 과 \sigma_{28})$ 변화를 측정하였다. 시험결과에 의하면, 기포재가 첨가되는 시간에서부터 60분, 90분 동안 방치하면 공기량은 감소된다. 동시에 압축강도는 점진적으로 증가된다. KSF 5405가 요구하는 slump값이 90분 이내에 $12\pm0.5$의 범위에 들어 가기 위해서는 기포재는 50,000cc/$\textrm{m}^3$-75,000cc/$\textrm{m}^3$만큼 첨가되어야 한다. 이때의 7일 압축강도가 170-200kg/$\textrm{cm}^2$이고 28일 압축강도는 215-290kg/$\textrm{cm}^2$이다. 이 값은 설계강도 $\sigma$28=210kg/$\textrm{cm}^2$ 보다 최고 약 40%까지 증가율을 보여 주었다.

• Proceedings of the Korea Concrete Institute Conference
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• 2009.05a
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• pp.115-116
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• 2009

A new model which is able to understand the mechanical behavior is developed, based on investigating the theoretical background for design compressive strength in strut-and-tie model. A proposed model is an alternative method for engineers through analyzing the merits and demerits of the conventional models

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.3A
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• pp.227-234
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• 2011

Recently, a high strength concrete of more than 40 MPa has been increasingly used in practice. However, use of the high strength concrete may influence on design parameters, particularly stress distribution. This is very true since the current everyday practice employs equivalent rectangular stress distribution that is derived from normal strength concrete. Subsequently, the stress distribution seems to be reevaluated and then a new distribution with new parameters needs to be suggested for the high strength concrete. For this purpose, linear and multiple regression analyses have been carried out in term of using experimental data for the high strength concrete of 40 to 80 MPa available in literatures. Accordingly, new parameters associated with the stress distribution have been proposed and employed for the design of flexural and compressive members. Comparative design examples indicate that designs with new parameters reduce section dimensions compared to those with the current code parameters for concrete strengths of 40 to 70 MPa. In particular, for compressive members, design with new parameters exhibit conservative compressive force compared to those with the current code parameters.

• Magazine of the Korea Concrete Institute
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• v.10 no.1
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• pp.119-124
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• 1998

콘크리트는 시멘트, 잔골재 및 굵은 골재, 물 및 첨가제의 양이나 투입순서 ,혼합방법등 여러 가지 요인에 따라 성질이 바뀌게 되는 복합재료이다. 따라서 넓은 의미에서 품질 판정의 한 수단이 되는 콘크리트의 설계기준강도 또는 압축강도 fc'(=28일 압축강도)는 물론 기타의 성질도 정확한 예측이 불가능하다. 즉 소요강도를 목표로 배합된 공시체의 시험결과는 예외없이 통계적 가변성을 나타낸다. 여기에서는 공시체의 7일 강도의 평균치 및 표준 편차와 공시체의 28일 강도 측정치로부터 콘크리트의 압축강도를 추정하는식을 제안하였다. 이를 위하여 7,320개의 강도시험자료를 수집한 후 이들을 선형 회귀 분석법으로 처리하였다. 제안된 식에 의한 콘크리트의 압축강도는 타 추정식에 의한 값보다 실측치에 좀 더 근접함을 보여주었다. 또한 제안식의 검정을 위해 서울지역 자료 5,200개를 수집하여 제안식과 JIS, Slater식과의 오차를 비교한 결과에 따르면 제안식이 더 안전측임을 알 수 있었다. 그리고 슈미트 햄머에 의한 현장 실측 강도와 제안식과의 콘크리트 강도 오차는 대체로 2.3%이었다.

• Journal of the Korea Concrete Institute
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• v.23 no.3
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• pp.365-376
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• 2011

The current Concrete Structural Design Code (2007) prescribe the equivalent rectangular stress block of the ACI 318 Building Code as concrete compressive stress distribution for design of concrete structures. The rectangular stress block may be enough for flexural strength calculation, but realistic stress-strain relationship is required for performance verification at selected limit state in performance-based design. Moreover, the ACI rectangular stress block provides non-conservative flexural strength for high strength concrete columns. Therefore a new stress distribution model is required for development of performance-based design code. This paper proposes a concrete compressive stress-strain distribution model for design and performance verification. The proposed model has a parabolic-rectangular shape, which is adopted by Eurocode 2 and Japanese Code (JSCE). It was developed by investigation of experimental test results conducted by the authors and other researchers. The test results cover high strength concrete as well as normal strength concrete. The stress distribution parameters of the proposed models are compared to those of the ACI 318 Building Code, Eurocode 2, Japanese Code (JSCE) and Canadian Code (CSA) as well as the test results.

• Journal of Korean Society of Steel Construction
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• v.10 no.4 s.37
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• pp.677-689
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• 1998

In relation to concentrically loaded compression, this research is to describe, analyze, and evaluate the design strength in steel stud. The similarity and difference among load and resistance factor design specification for cold-formed steel structural members (AISI), cold-formed thin gauge members and sheeting (EC3 part 1.3), and German draft (DASt-Richtlinie 016) are introduced, discussed, and systematically evaluated. Especially, the effective width and global instability problems (flexural buckling and torsional flexural buckling) are here implied in this research. The design axial strength by dual standards (AISI and EC3) is calculated and compared using the example.

• Journal of Korean Society of Steel Construction
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• v.28 no.4
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• pp.253-261
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• 2016

In order to evaluate compressive strength of centrally-loaded steel column at elevated temperature, new FE analysis techniques and assumptions of model were applied in this study. It also includes comparison with the existing studies, and a new design equation for centrally-loaded steel column at elevated temperature was proposed. The proposed equation was the most accurate of the three design equations(EC3, AISC, proposed equation) when comparing with the coefficient of determination on the simulated results and test results.

• Journal of the Korean Recycled Construction Resources Institute
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• v.3 no.3
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• pp.206-211
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• 2015

Recently, for UHPC (Ulta High Performance Concrete) which is researched actively, as the tensile strength is absolutely influenced on the content of steel fiber, in this paper, experiments of compressive strength, elasticity modulus and tensile strength were performed according to compressive strength and content of steel fiber as variables. By the test results, compressive strength, elasticity modulus and tensile strength are proportioned and have a good correlation and according to content of steel fiber, compressive and tensile strength are also proportioned and have a good correlation. In case of elasticity modulus, the difference between test and present design code is not large, so it is possible to adapt to present design code. On the other hand, in case of tensile strength, as there is no specification of present design code, new prediction equation is proposed by using nonlinear regression analysis and the proposed equation have a good correlation to test results.

• Journal of Korean Society of Steel Construction
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• v.29 no.2
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• pp.123-134
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• 2017

Ultimate axial strength of longitudinally stiffened cylindrical steel shells for wind turbine tower was investigated by applying the geometrically and materially nonlinear finite element method. The effects of radius to thickness ratio of shell, shape and amplitude of initial imperfections, area ratio between effective shell and stiffener, and stiffener spacing on the ultimate axial strength of cylindrical shells were analyzed. The ultimate axial strengths of stiffened cylindrical shells by FEA were compared with design buckling strengths specified in DNV-RP-C202. The shell buckling modes obtained from a linear elastic bifurcation FE analysis as well as the weld depression during fabrication specified in Eurocode 3 were introduced in the nonlinear FE analysis as initial geometric imperfections. The radius to thickness ratio of cylindrical shell models was selected to be in the range of 50 to 200. The longitudinal stiffeners were designed according to DNV-RP-C202 to prevent the lateral torsional buckling and local buckling of stiffeners.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.2
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• pp.1-9
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• 2016

The authors performed the experimental work to propose the strength prediction equation for high strength concrete based on the non-destructive test methods. The concrete specimens that the range of design compressive strength was 40~80 MPa was produced in laboratory, and then tested rebound test and ultrasonic velocity methods and also compressive test according to the Korea Standard. The test results was compared with previously equations suggested by other researcher. From the test, these traditional nondestructive methods are simple, quick, has proven to be reliable and useful method for predicting the concrete strength. The test results were compared with the previous equations and then newly proposed own equations based on the test results. The proposed equations have the suitable precision and accuracy for applying the high strength concrete structures.