• Computers and Concrete
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• 제19권5호
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• pp.477-488
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• 2017

In this paper, an innovative technique for finite element (FE) modeling of steel tube-confined concrete (STCC) columns with active confinement under axial compressive loading is presented. In this method, a new constitutive model for the stress-strain relationship of actively-confined concrete is proposed. In total, 14 series of experimental STCC stub columns having active confinement were modeled using the ABAQUS software. The results obtained from the 3D model including the compressive strength at the initial peak point and failure point, as well as the axial and lateral stress-strain curves were compared with the experimental results to verify the accuracy of the 3D model. It was found that there existed a good agreement between them. A parametric study was conducted to investigate the effect of the concrete compressive strength, steel tube wall thickness, and pre-stressing level on the behavior of STCC columns with active confinement. The results indicated that increasing the concrete core's compressive strength leads to an increase in the compressive strength of the active composite column as well as its earlier failure. Furthermore, a reduction in the tube external diameter-to-wall thickness ratio affects the axial stress-strain curve and the confining pressure, while increasing the pre-stressing level has a negligible effect on the two.

• 한국건설순환자원학회논문집
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• 제6권4호
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• pp.311-318
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• 2018

이 연구에서는, 기둥 횡방향 철근의 화재 후 잔존 역학적 특성 규명 연구의 일환으로, 횡철근비와 기둥의 고온 노출면 수 차이에 따른 횡방향 철근의 손실강도 보상효과를 잔존 압축강도, 변형률 및 탄성계수와 하중-변위 곡선의 상대적 비교분석을 통해 규명하였다. 실험변수로 띠철근의 간격과 고온 노출면 수를 변수로 한 실험체를 제작하여 가열실험을 수행하였다. 이때 전기로 온도를 $400^{\circ}C$, $600^{\circ}C$ 및 $800^{\circ}C$로 설정하여 $13.33^{\circ}C$/분의 속도로 가열하고 2시간동안 그 온도를 유지시켰다. 냉각된 실험체에 대해 응력-변형률 곡선을 구하기 위한 압축실험을 수행하고, 이로부터 탄성계수, 잔존 내력 및 변형률 등의 잔존 역학적 특성을 분석하였다. 실험결과, 고온 노출 면이 많은 기둥이 수열온도 증가에 따라 탄성계수 감소율이 크게 나타나고, 횡철근비가 크면 수열온도 증가에 따라 탄성계수 감소율이 작게 나타났는데, 이로부터 기둥위치와 횡철근비 등이 내화설계나 화재 안전진단 시 고려되어 합리적인 내화성능 평가가 이루어져야 할 것으로 여겨진다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 춘계학술발표회 논문집(I)
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• pp.62-65
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• 2006

This study investigated the behavior of R/C column confined with headed crossties subjected to eccentric loading. The 16 specimens are designed to have adequate confinement steel, determined by ACI seismic design. The variables studied in this research test are eccentricity to depth ratios, spacing of lateral steel and the anchor type of end of crossties. From the test results, all columns showed similar behavior up to the peak load but those columns laterally confined with head presented more ductile behavior after the peak load. The comparisons indicate that the flexural behavior of confined-concrete columns can be computed resonable accurately by P-M interaction curve.

• 콘크리트학회논문집
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• 제12권4호
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• pp.3-14
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• 2000

Structural performance of the walls subjected to lateral load reversals depends on various parameters such as loading history, sectional shape, reinforcement, lateral confinement, aspect ratio, axial compression, etc. Thus, the performance of the shearwall for wall-type apartment should be evaluated properly considering above parameters. This study investigates the effect of sectional shape on the structural performance of the wall. Sectional shape of the specimen is rectangular, barbell and T. Based on this experimental results, all specimens behaved as ductile fashion and failed by concrete crushing of the compression zone. Deformation index of those specimens evaluated better than 3 of ductility ratio, and 1.5% of deformability specified by seismic provision. Moreover, the performance of the rectangular shaped specimen, whose compression zone was confined with U-bar and cross tie, was as good as the barbell shaped specimen. Therefore, if we considered construction practice such as workmanship and detailing, shearwall with rectangular section may be more economical lateral load resisting system.

• 콘크리트학회지
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• 제7권3호
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• pp.199-210
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• 1995

충전형 강관콘크리트 구조는 강관과 콘크리트 두 재료의 이질적인 재료특성을 상호 보완적으로 발휘하여 구조적 성능향상을 꾀한 것으로서 제구조 특성상 우수한 구조형식이라 할 수 있다. 강관으로 구속된 콘크리트가 중심축력을 받게 되면 내부의 콘크리트는 압괴에 의한 체적 팽창을 외부의 강관에 의해 구속 받게 되므로 3축 압축응력 상태로 되어 압축강도가 증대된다. 또한 콘크리트의 압괴에 의한 탈락 현상이 방지되므로서 단면의 결손이 없어져 내력 저하가 작아진다는 잇점을 가진다. 따라서 본 연구에서는 원형강관으로 구속된 내부 콘크리트의 구조적 거동 특성을 규명하기 위한 것으로서 폭두께비와 충전 콘크리트의 강도를 주요 변수로 하여 일련의 실험을 통하여 강관으로 구속(3축 응력)된 콘크리트의 구조적 거동 특성을 고찰하였다. 일련의 실험을 통하여 얻어진 결론을 요약하면 다음과 같다. (1)강관에 의한 콘크리트의 구속효과는 강관의 폭두께비와 충전 콘크리트의 강도가 낮을수록 현저하며, 원형강관으로 구속된 내부 콘크리트는 최대내력시의 변형능력에 있어서 횡방향 구속이 없는 콘크리트보다 4~7배 정도까지 증대시켜 연성효과를 높일 수 있을 것으로 기대된다. (2)콘크리트의 구속계수를 이용하여 강관으로 구속된 내부 콘크리트의 강도와 콘트리트 충전강관 기둥의 최대내력을 산정할 수 있는 식을 제시하였다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1998년도 가을 학술발표대회 논문집(III)
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• pp.609-614
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• 1998

Lateral pressure by tied reinforcement greatly enhances the maximum strength and ductility of columns under concentric loading. The lateral confinement effects will be improves ductility of high-strength concrete. The major purpose of this paper is to study on the improvements of maximum strength and strain at the point of tied high-strength concrete columns subject to axial loads. For this purpose, this study collected the other analytical results and the experimental data that has been performed by a lot of worldwide researchers and also analyzed it statistically. As the result, the theoretical equation for predict maximum strength and strain at the point was proposed. It is based on calculation of lateral confinement pressure generate from tensile that develop in transverse reinforcement.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 가을 학술발표회 논문집
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• pp.477-482
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• 2001

This paper is to study the effect of longitudinal reinforcement ratios and axial deformation on the frame analysis in reinforced concrete(RC) columns and to investigate the effect of confined concrete core, the length-width ratio and longitudinal steel ratios on frame analysis in Concrete-Filled steel Tubular(CFT) columns. An equation if derived to evaluate the modulus of elasticity for core concrete. The 34 reference data have been collected for the purpose and are processed by the mean of a multiple regression analysis technique. The equation and longitudinal reinforcement ratios was applied to RC columns for structural analysis. Then, the difference of beam moment was identified. In general, the results of analysis was indicated reasonable differences in beam moment, in case of longitudinal reinforcement ratios applied to RC columns when compared with the plain concrete columns. In CFT columns the equation was also applied in order to the effect of confined concrete core on structural analysis. Beam moment was increased as volumetric ratio of lateral steel was decreased. The effect of longitudinal steel ratios was investigated in CFT columns and was confirmed beam moment variety. The result was appeared reasonable difference in beam moment as longitudinal steel was increased.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2000년도 봄 학술발표회 논문집
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• pp.433-439
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• 2000

Reinforced concrete beams show increased ductile behavior when the compressive concrete is confined with transverse steel. In the inelastic range, the most variations of ductile behaviour are defined the equivalent length of the plastic hinge and the plastic hinge rotation. In an investigation to study the influence of such confinement, sixteen reinforced concrete beams were tested in flexure and the deflections noted at all stages of loading. For all the beams tested, the plastic hinge rotation have been computed and the effect of confinement on the same examined. The conclusions are summarized as follows: The equivalent lengths of the plastic hinge are ranged within the effective depth comparatively. The ability of the plastic hinge rotation of the reinforced concrete beams confined with transverse steel are enlarged when transverse reinforcement content are increased, but the spaces are more important as the shear force are largely increased.

• International Journal of Concrete Structures and Materials
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• 제11권1호
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• pp.135-149
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• 2017

The prediction of the actual ultimate capacity of confined concrete columns requires partial confinement utilization under eccentric loading. This is attributed to the reduction in compression zone compared to columns under pure axial compression. Modern codes and standards are introducing the need to perform extreme event analysis under static loads. There has been a number of studies that focused on the analysis and testing of concentric columns. On the other hand, the augmentation of compressive strength due to partial confinement has not been treated before. The higher eccentricity causes smaller confined concrete region in compression yielding smaller increase in strength of concrete. Accordingly, the ultimate eccentric confined strength is gradually reduced from the fully confined value $f_{cc}$ (at zero eccentricity) to the unconfined value $f^{\prime}_c$ (at infinite eccentricity) as a function of the ratio of compression area to total area of each eccentricity. This approach is used to implement an adaptive Mander model for analyzing eccentrically loaded columns. Generalization of the 3D moment of area approach is implemented based on proportional loading, fiber model and the secant stiffness approach, in an incremental-iterative numerical procedure to achieve the equilibrium path of $P-{\varepsilon}$ and $M-{\varphi}$ response up to failure. This numerical analysis is adapted to assess the confining effect in rectangular columns confined with conventional lateral steel. This analysis is validated against experimental data found in the literature showing good correlation to the partial confinement model while rendering the full confinement treatment unsafe.

• 콘크리트학회논문집
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• 제24권6호
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• pp.643-650
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• 2012

콘크리트구조설계기준에서는 철근콘크리트 기둥에서 주철근의 설계기준항복강도를 550 MPa 이하로 규정하고 있다. 이는 철근콘크리트 기둥에 주철근으로 고강도 철근(high-strength concrete)을 사용할 때 콘크리트가 압축강도에 도달하여도 주철근이 항복변형률에 도달하지 않아 고강도 철근을 효율적으로 사용할 수 없기 때문이다. 철근의 설계기준항복강도 제한의 문제점을 해결하기 위한 방법으로는 횡구속력(confinement effect)을 가해주는 방법과 콘크리트의 파괴변형률(peak strain)을 증진시켜주는 방법이 있다. 횡구속을 효과적으로 가하는 방법으로서 원형 단면의 철근보다는 판재를 사용하는 것이 바람직하다. 이 연구에서는 가공이 용이한 판재로서 탄소섬유판을 철근콘크리트 기둥에서 횡구속효과를 위한 구조재료로 사용하였을 경우 보강되지 않은 경우보다 증진된 압축강도 및 축압축 파괴변형률을 보였으며, 콘크리트 단면 형상이 원형에 가까울수록, 횡구속 형태가 원형에 가까울수록 횡구속 효과는 더욱 커졌다. 최종적으로 실험 결과를 토대로 철근콘크리트 기둥에서 탄소섬유판에 의한 횡구속 효과와 함께 고강도 철근의 적용 가능성을 확인하였다.