• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1995년도 봄 학술발표회 논문집
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• pp.124-129
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• 1995

In this study proposed to rapid and simple methid of test for early evaluation of strength of cement. The obtained results through a series of experiment are summarized as follow. The resistance ratio was decreased as the increase of water-cement ratio. The compressive strength of cement was increased as the resistance ratio increase. The experimental results of compressive strength of cement is shown in the same value no relation with the kind of cement respectively.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2019년도 춘계 학술논문 발표대회
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• pp.168-169
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• 2019

This study examined the effect of foam volume ratio and curing temperature the air dry density and compressive strength of lightweight concrete using bottom ash. Test results showed that the lightweight concrete possessed the compressive strength of 3.4~22.7 MPa at the air dry density of 1,041~1,583 kg/m3.

• Structural Engineering and Mechanics
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• 제65권2호
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• pp.163-171
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• 2018

Plain concrete is a brittle material with a very low tensile strength compared to compressive strength and critical tensile strain. This study analyzed the dynamic characteristics of high-performance fiber-reinforced cementitious composites based on slurry-infiltrated fiber concrete (SIFCON-based HPFRCC), which maximizes the steel-fiber volume fraction and uses high-strength mortar to increase resistance to loads, such as explosion and impact, with a very short acting time. For major experimental variables, three levels of fiber aspect ratio and five levels of fiber volume fraction between 6.0% and 8.0% were considered, and the flexural strength and toughness characteristics were analyzed according to these variables. Furthermore, three levels of the aspect ratio of used steel fibers were considered. The highest flexural strength of 65.0 MPa was shown at the fiber aspect ratio of 80 and the fiber volume fraction of 7.0%, and the flexural strength and toughness increased proportionally to the fiber volume fraction. The test results according to fiber aspect ratio and fiber volume fraction revealed that after the initial crack, the load of the SIFCON-based HPFRCC continuously increased because of the high fiber volume fraction. In addition, sufficient residual strength was achieved after the maximum strength; this achievement will bring about positive effects on the brittle fracture of structures when an unexpected load, such as explosion or impact, is applied.

• Earthquakes and Structures
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• 제12권4호
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• pp.397-407
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• 2017

To estimate the structural seismic demand, some methods are based on an equivalent linear system such as the Capacity Spectrum Method, the N2 method and the Equivalent Linearization method. Another category, widely investigated, is based on displacement correction such as the Displacement Coefficient Method and the Coefficient Method. Its basic concept consists in converting the elastic linear displacement of an equivalent Single Degree of Freedom system (SDOF) into a corresponding inelastic displacement. It relies on adequate modifying or reduction coefficient such as the inelastic deformation ratio which is usually developed for systems with known ductility factors ($C_{\mu}$) and ($C_R$) for known yield-strength reduction factor. The present paper proposes a rational approach which estimates this inelastic deformation ratio for SDOF bilinear systems by rigorous nonlinear analysis. It proposes a new inelastic deformation ratio which unifies and combines both $C_{\mu}$ and $C_R$ effects. It is defined by the ratio between the inelastic and elastic maximum lateral displacement demands. Three options are investigated in order to express the inelastic response spectra in terms of: ductility demand, yield strength reduction factor, and inelastic deformation ratio which depends on the period, the post-to-preyield stiffness ratio, the yield strength and the peak ground acceleration. This new inelastic deformation ratio ($C_{\eta}$) is describes the response spectra and is related to the capacity curve (pushover curve): normalized yield strength coefficient (${\eta}$), post-to-preyield stiffness ratio (${\alpha}$), natural period (T), peak ductility factor (${\mu}$), and the yield strength reduction factor ($R_y$). For illustrative purposes, instantaneous ductility demand and yield strength reduction factor for a SDOF system subject to various recorded motions (El-Centro 1940 (N/S), Boumerdes: Algeria 2003). The method accuracy is investigated and compared to classical formulations, for various hysteretic models and values of the normalized yield strength coefficient (${\eta}$), post-to-preyield stiffness ratio (${\alpha}$), and natural period (T). Though the ductility demand and yield strength reduction factor differ greatly for some given T and ${\eta}$ ranges, they remain take close when ${\eta}>1$, whereas they are equal to 1 for periods $T{\geq}1s$.

• 콘크리트학회논문집
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• 제15권2호
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• pp.246-253
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• 2003

콘크리트 부재는 직접 인장력에 저항하도록 설계되지는 않는 것이 일반적이나, 부재의 균열강도 등을 산정하기 위해서는 반드시 확인하여야 하는 재료 특성 중의 하나이다. 콘크리트의 인장강도 시험방법은 주로 직접인장, 휨인장, 쪼갬인장의 3가지로 구분하고 있으나, 이 중 직접인장시험법은 시험체에 순수인장력을 가력할 수 있는 실험방법상의 문제로 거의 수행되지 못하여 온 것이 사실이다. 본 연구에서는 직접인장시험방법의 검토 및 시험체의 세장비, 크기 등이 직접인장강도에 미치는 영향에 대하여 연구하였다. 단부 보강편을 이용한 직접인장강도의 실험은 RILEM 및 U.S.Bureau of Reclamation의 규정을 사용하였으며, 총 4가지 종류의 세장비와 2가지 크기의 시험체에 대한 연구를 수행하였다. 실험의 결과는 동일변수의 쪼갬인장강도 및 휨인장강도와 비교$.$분석을 실시하였으며, 이를 신뢰성있는 선행 연구자들의 연구결과와 비교하여 그 타당성을 검증하였다.

• 대한토목학회논문집
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• 제36권6호
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• pp.1117-1123
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• 2016

롤러전압콘크리트포장 공법은 기존 시멘트 콘크리트 공법의 재료 특성 및 아스팔트 포장의 시공특성을 공유하는 포장 방식이다. 일반 시멘트 콘크리트 포장의 우수한 구조적 성능을 유지하면서, 아스팔트 시공 장비를 사용하여 간소한 시공절차로 경제성을 확보할 수 있다. 롤러전압콘크리트포장 공법은 수화반응과 롤러다짐에 의한 골재 맞물림 효과로 일반 시멘트 콘크리트 포장보다 적은 시멘트량을 사용하여도 충분한 강도를 발현할 수 있다. 또한 일반 시멘트 콘크리트 포장과 동등한 강도 특성을 발휘 할 수 있으며, 본 연구에서는 RCCP의 다짐도와 압축강도의 관계를 정량적으로 도출하고자 한다. 롤러전압콘크리트의 다짐에너지를 변화시키면서 다양한 다짐도를 갖는 시편을 제작하였다. 다짐도는 시편의 건조단위중량과 최대건조단위중량의 비로 정의하였으며, 다양한 다짐도로 성형된 시편의 28일 압축강도를 평가하였고, 다짐도에 따른 강도비의 관계를 도출 하였다. 따라서 롤러전압콘크리트 공법의 국내 현장적용을 위한 다짐도에 따른 강도비의 중요성을 부각하여 현장 다짐도 관리에 적용할 수 있을 것으로 판단된다.

• Earthquakes and Structures
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• 제13권1호
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• pp.59-66
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• 2017

Modern seismic codes rely on performance-based seismic design methodology which requires that the structures withstand inelastic deformation. Many studies have focused on the inelastic deformation ratio evaluation (ratio between the inelastic and elastic maximum lateral displacement demands) for various inelastic spectra. This paper investigates the inelastic response spectra through the ductility demand ${\mu}$, the yield strength reduction factor $R_y$, and the inelastic deformation ratio. They depend on the vibration period T, the post-to-preyield stiffness ratio ${\alpha}$, the peak ground acceleration (PGA), and the normalized yield strength coefficient ${\eta}$ (ratio of yield strength coefficient divided by the PGA). A new inelastic deformation ratio $C_{\eta}$ is defined; it is related to the capacity curve (pushover curve) through the coefficient (${\eta}$) and the ratio (${\alpha}$) that are used as control parameters. A set of 140 real ground motions is selected. The structures are bilinear inelastic single degree of freedom systems (SDOF). The sensitivity of the resulting inelastic deformation ratio mean values is discussed for different levels of normalized yield strength coefficient. The influence of vibration period T, post-to-preyield stiffness ratio ${\alpha}$, normalized yield strength coefficient ${\eta}$, earthquake magnitude, ruptures distance (i.e., to fault rupture) and site conditions is also investigated. A regression analysis leads to simplified expressions of this inelastic deformation ratio. These simplified equations estimate the inelastic deformation ratio for structures, which is a key parameter for design or evaluation. The results show that, for a given level of normalized yield strength coefficient, these inelastic displacement ratios become non sensitive to none of the rupture distance, the earthquake magnitude or the site class. Furthermore, they show that the post-to-preyield stiffness has a negligible effect on the inelastic deformation ratio if the normalized yield strength coefficient is greater than unity.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1999년도 봄 학술발표회 논문집(I)
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• pp.307-312
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• 1999

The purpose of this study is to ascertain the strength properties of water-permeable concrete with redispersible polymer powder, silica fume and polypropylene fibers. The water-permeable concrete using rediapersibel polymer powder with a water-cement ratio of 25%, polymer-cement ratios of 0 to 10%, silica fume contents of 0 to 10% and fiber contents of 0 to 1.5% are prepared, and tested for flexural strength, compressive strength and water permeability. From the test results, improvements in the strength properties of the water-permeable concrete due to the addition of the redispersible polymer powder, silica fume and fibers are discussed. It is concluded from the test results that the superior flexural and compressive strengths of water-permeable concretes are obtained at a propylene fiber content of 1.0% with a void filling ratio of 50%. And, the water-permeable concrete having a flexural strength of 15.6~28.4kgf/$\textrm{cm}^2$, a compressive strength of 63.5~120.6kgf/$\textrm{cm}^2$, and a coefficient of permeability of 1.14~1.70cm/s at a void filling ratio of 30% can be prepared. Also water-permeable concrete having a flexural strength of 35.6~57.9kgf/$\textrm{cm}^2$, a compressive strength of 164.0~290.0kgf/$\textrm{cm}^2$, and a coefficient of permeability of 0.19~1.04cm/s at a void filling ratio of 50% can be prepared in the consideration of the mix proprotioning factors.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2007년도 춘계학술논문 발표대회
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• pp.55-58
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• 2007

This study investigates the spatting properties of high strength concrete, $60\sim80MPa$ class, designed with diverse aspect ratios and fiber content of nylon(NY). Test showed that increase of fiber content and aspect ratio in concrete decreased the fluidity of fresh concrete, especially for 1580 and 3000 aspect ratio of fiber. As for the compressive and tensile strength, adding NY fiber did not significantly affect the values In the range of high strength. After completing the fire test, the specimens containing both 750 and 1000 aspect ratios of fiber protected the spatting occurrence even in 0.05vol.% of fiber content. This specimens indicated the residual compressive strength ratio at 37%, showing the most favorable value among other specimens. Therefore, it is demonstrated that to protect the spalling in high strength concrete considering the effective fluidity, strength and economic efficiency altogether, adding 0.05vol.% of NY fiber with 750 aspect ratio Is beneficial.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1995년도 가을 학술발표회 논문집
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• pp.284-292
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• 1995

This paper is on experimental study on the behavior of reinforced concrete columns subjected to longitudinal steel ratio To investigate the effects of concrete strength and longitedinal steel ratio on the behavior of reinforced concrete columns. a series of tests were carried out for thirty-six tied reinforced concrete columns with a 100mm square cross section and three slendemess ratio of 15, 30 and 50. And To study and illustrate the change of the ultimate loads and that of displacements, two different concrete strength of 180,26kfg/$\textrm{cm}^2$, 819,36kfg/$\textrm{cm}^2$ and five different longitudinal steel ratio of 0.5, 1.0, 4.0, 5.7 and 10.3% were used. The boundary conditions at the ends were both hinged and the end eccentricities (17mm) were equal and of the same sign. While the ultimate load capacity of high-strength concrete column was much increased when the columns were short, that was not when the columns were slender. The effect of longitudinal steel ratio on the increased of ultimate load of column was more evident for slender columns than for short ones and the ultimate of longitudinal steel ratio were more pronounced with increasing concrete strength. The more inserted the longitudinal steel, the more increased the ultimate load, but the superabundance of longitudinal steel ratio over the limitation of maximum steel ratio in ACI code was used, it was showed that the ultimate load was rather decreased.