• Advances in concrete construction
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• 제11권3호
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• pp.193-206
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• 2021

Extensive research has been conducted on the basic mechanical property and structural applications of engineered cementitious composites (ECC). Despite the high tensile ductility and high toughness of ECC, transverse steel reinforcement is still necessary to confine ECC for high performance. However, limited research has examined performance of ECC confined with practical amount of transverse reinforcement. This paper presents the results of axial compression tests on 14 square ECC columns and 4 conventional concrete columns (used as control specimens) with transverse reinforcement. The test variables were spacing, configuration (square ties or square and diamond shape ties), and yield strength of stirrups. The test showed that ECC columns confined with steel stirrup had good compressive ductility, and the stirrup spacing had the greatest effect on the compressive performance. The self-confinement effect of ECC results in a more uniform but slower expansion of the whole column compared with CC ones. The test results are then compared against the predictions from a number of existing models for conventional confined concrete. It is indicated that these models fail to predict the axial strains at peak axial stress and the trend of the stress-strain curve of steel stirrups-confined ECC with sufficient accuracy. Several new equations are then proposed for the compressive properties of steel-confined ECC based on test results and potential approaches for future studies are proposed.

• 콘크리트학회논문집
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• 제16권5호
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• pp.687-696
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• 2004

철근콘크리트 교각의 시공시 소성힌지구간에서 주철근 겹침이음은 내진성능면에서 바람직하지 않으나 불가피하게 시공되는 경우가 있었다. 특히, 1992년 도로교표준시방서의 내진설계 기준이 마련되기 이전에 설계 시공된 대부분의 철근콘크리트 교각은 소성힌지구간에 주철근을 겹침이음 하였으며, 이들은 휨에 대한 소성영역에서의 거동에 직접적인 영향을 미친다. 본 연구에서는 직경 1.2m, 형상비 4.0의 휨파괴가 예상되는 비내진 및 한정연성시험체를 8기 제작하여 준정적(Quasi-Static)실험을 통한 철근콘크리트(RC) 교각의 소성힌지구간내의 주철근 겹침이음과 횡방향구속력이 내진성능에 미치는 영향을 평가하였다. 실험체의 변수로서는 $0\%,\;50\%,\;100\%$의 주철근 겹침이음, 2종류의 횡구속철근비 및 띠철근 형상을 선택하였다. 연구결과 주철근 겹침이음 정도에 따라 철근콘크리트 교각의 내진성능은 급격히 저하되었으며, 겹침이음이 없는 한정연성설계된 시험체의 경우 높은 내진성능을 발휘하였다. 연구결과에 따라 중저진지역에서 겹침이음된 주철근 교각의 내진성능을 위한 적절한 횡방향철근량을 제안하였다.

• 콘크리트학회논문집
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• 제16권1호
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• pp.61-69
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• 2004

신설교량의 경우 최근 개정된 도로교설계기준에 의해 내진설계를 수행하여 시공되었으나, 내진설계규정이 적용되기 이전에 시공되어 사용중에 있는 철근콘크리트 교각의 경우에는 지진에 의한 횡하중에 대해 취약할 수 있다. 특히 형상비가 큰 기존 교각에서는 기초와 교각 접합부에 주철근 겹침이음이 존재하므로 지진이 발생할 경우 피복콘크리트 파손에 따른 부착파괴 형태의 급격한 취성파괴 거동을 나타낸다. 이러한 부착파괴가 일어나는 소성힌지 구간에 FRP 적층 원통관으로 보강하여 부착강도를 크게 함으로써 횡하중에 대한 급격한 파괴를 예방할 수 있다. 따라서 본 연구에서는 FRP 적층 원통관으로 보강된 원형교각에서 FRP 적층 원통관이 주는 구속효과를 효과적으로 산정하기 위한 이론식을 유도하여 제안하고자 하였다. 이를 위해 FRP 적층 원통관이 철근콘크리트 원형교각에 발생시키는 구속응력을 이론적으로 유도하여 제안하였으며, 제안된 식의 타당성을 검증하기 위해 기존의 타 연구에서 수행한 실험결과와 비교, 검토하였다. 또한 다양한 FRP 적층조건에 따른 구속응력의 변화를 고찰하기 위한 매개변수 연구를 수행하였다. 이와 같은 연구를 통해 본 연구에서 제안하는 식이 FRP 적층 원통관을 이용하여 보강한 기존 원형교각의 거동을 잘 예측할 수 있음을 확인하였으며, 적층수, 섬유배향각, 섬유방향의 탄성계수가 FRP 적층 원통관에 의한 내진보강효과에 가장 지배적인 매개인자임을 알 수가 있었다.

• Advances in concrete construction
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• 제10권4호
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• pp.279-287
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• 2020

The practice of splicing reinforcing bars in reinforced concrete structures to manage insufficient bar length is a common approach, which is mainly due to transportation limitations on bar length. The splicing of reinforcing bars side by side offers a simple and economical solution to the problem of continuity. This paper examines the influence of different structural parameters such as concrete cover, lap splice length, shear links confinement and concrete strength on the lap splices based on an extensive experimental database of laps and anchorage. The current study shows that increasing the lap splices beyond 50Ø has no additional benefit for increasing its strength. The results also show that relative to the measured stress, specimens with larger concrete side covers shows higher splice stress compared to the samples with smaller concrete covers.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2005년도 학술발표회 논문집
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• pp.361-371
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• 2005

The confined concrete subjected multi-axial stresses have been known as the fact it increases strength of concrete significantly compared with unconfined concrete. Many researchers have studied in confining effects of concrete, and now are studying in many fields. Although many researches about confined concrete using FRP have been studied recently, it is difficult to apply concrete confined by FRP in real structures because FRP is a brittle material. To investigate the influence of concrete strength and ductility increased by confining stiffness in steel, this study was tested and compared with 51 specimens confined by different shapes and thicknesses of steel tube. This test verified the increasement of strength and ductility in confined concrete. Also, analyzing the experimental data by regression method, this study provides stress-strain model about CSS and R4S considering effect of confinement stiffness on the stress-strain relations of concrete.

• 대한토목학회논문집
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• 제31권4A호
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• pp.331-340
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• 2011

콘크리트 공시체의 압축강도와 연성성능을 향상시키기 위하여 섬유-강판 복합플레이트 fiber-sheet and steel-plate composite plate(FSP))의 적용을 실험적으로 연구하였다. FSP 보강재료, 앵커볼트 설치방법, 콘크리트 압축강도 등이 고려된 FSP 보강 콘크리트 공시체의 압축실험을 실시하였다. FSP 보강 콘크리트 공시체의 압축실험결과, FSP는 콘크리트 공시체의 압축강도와 변형저항성능을 크게 향상시켰다. FSP 보강 콘크리트 공시체의 압축성능은 FSP 보강재 종류, 앵커볼트 사용방법, 콘크리트 압축강도에 영향을 받는 것으로 나타났다. 앵커볼트를 사용한 FSP 보강 콘크리트 공시체 실험에서 측정된 FSP의 파단변형률은 FRP 보강 콘크리트 압축부재 실험에서 측정된 FRP 파단변형률보다 크게 측정되었다. FSP 파단변형률의 크기는 FSP의 보강효과에 영향을 미친다. FSP 보강 콘크리트 공시체 압축실험에서 측정된 축방향변형률, 원주방향변형률, 체적 변형률에 의한 FSP 내부 콘크리트의 손상상태를 분석하여 FSP 보강효과를 평가하였다. 연구결과, FSP 보강공법은 콘크리트 압축부재의 보강방법으로 실용적 기법이라 판단된다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 추계 학술발표회 제17권2호
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• pp.5-8
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• 2005

The purpose of this study is to investigate the mechanical characteristics of plain and steel fiber high strength concrete under uniaxial and biaxial loading condition. A number of plain and steel fiber high strength concrete cubes having 28 days compressive strength of 82.7Mpa (12,000psi) were made and tested. Four principal compression stress ratios, and four fiber concentrations were selected as major test variables. From test results, it is shown that confinement stress in minor stress direction has pronounced effect on the strength and deformational behavior. Both of the stiffness and ultimate strength of the plain and fiber high strength concrete increased. The maximum increase of ultimate strength occurred at biaxial stress ratio of 0.5 in the plain high strength concrete and the value were recorded 30 percent over than the strength under uniaxial condition. The failure modes of plain high strength concrete under uniaxial compression were shown as splitting type of failure but steel fiber concrete specimens under biaxial condition showed shear type failure.

• 콘크리트학회논문집
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• 제12권3호
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• pp.57-66
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• 2000

The ductility is an important consideration in the design of reinforced concrete structures. In the seismic design of reinforced concrete columns, it is necessary to allow for relatively large ductilities that the seismic energy be absorbed without shear failure of significant strength degradation after the reinforcement yielding in columns. Therefore, prediction of the ductility should be as accurate as possible. This research investigate the ductile behavior of rectangular reinforced high-strength concrete columns like as bridge piers with confinement steel. The effects on the ductility of axial load, lateral reinforcement ratio, longitudinal reinforcement ratio, shear span ratio, and compressive strength of concrete were investigated analytically using layered section analysis. as the results, it was proposed the proper relationship between ductility and variables and formulated into equations.

• 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%

• Steel and Composite Structures
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• 제6권1호
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• pp.55-69
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• 2006

The results of tests conducted on 11 concrete-filled steel tubular columns were reported. Concrete was partially filled in circular steel tubular columns. The primary test parameters were radius and thickness of steel tubes, concrete height, loading patterns and attachment of diaphragm and studs. Concrete strain was measured directly by embedding strain gauges so that the effect of diaphragm on concrete confinement could be investigated. The effects of concrete height and diaphragm on ultimate strength and ductility of steel tubes were investigated. The comparisons of the test results with the existing results for rectangular cross-sections were made on the basis of ultimate strength and ductility of concrete-filled steel tubular columns.