• Steel and Composite Structures
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• 제7권2호
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• pp.135-160
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• 2007

Recently, CFT column has been well-studied and reported on, because a CFT column has certain superior structural properties as well as good productivity, execution efficiency, and improved rigidity over existing columns. However, CFT column still has problems clearing the capacity evaluation between its steel tube member and high-strength concrete materials. Also, research on concrete has examined numerical values for high-strength concrete filled steel square tube columns (HCFT) to explain transformation performance (M-${\phi}$) when a short-column receives equal flexure-moment from axial stress. Moment-curvature formulas are proposed for HCFT columns based on analytic assumption described in this paper. This study investigated structural properties (capacity, curvature), through a series of experiments for HCFT with key parameters, such as strength of concrete mixed design (58.8 MPa), width-thickness ratio (D/t), buckling length to sectional width ratio (Lk/D) and concrete types (Zeolite, Fly-ash, Silica-fume) under eccentric loads. A comparative analysis executed for the AISC-LRFD, AIJ and Takanori Sato, etc. Design formulas to estimate the axial load (N)-moment (M)-curvature (${\phi}$) are proposed for HCFT columns based on tests results described in this paper.

• Steel and Composite Structures
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• 제42권5호
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• pp.617-631
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• 2022

To study the eccentric compressive performance of the basalt-fiber reinforced recycled aggregate concrete (BFRRAC)-filled circular steel tubular stub column, 8 specimens with different replacement ratios of recycled coarse aggregate (RCA), basalt fiber (BF) dosage, strength grade of recycled aggregate concrete (RAC) and eccentricity were tested under eccentric static loading. The failure mode of the specimens was observed, and the relationship curves during the entire loading process were obtained. Further, the load-lateral displacement curve was simulated and verified. The influence of the different parameters on the peak bearing capacity of the specimens was analyzed, and the finite element analysis model was established under eccentric compression. Further, the design-calculation method of the eccentric bearing capacity for the specimens was suggested. It was observed that the strength failure is the ultimate point during the eccentric compression of the BFRRAC-filled circular steel tubular stub column. The shape of the load-lateral deflection curves of all specimens was similar. After the peak load was reached, the lateral deflection in the column was rapidly increased. The peak bearing capacity decreased on enhancing the replacement ratio or eccentric distance, while the core RAC strength exhibited the opposite behavior. The ultimate bearing capacity of the BFRRAC-filled circular steel tubular stub column under eccentric compression calculated based on the limit analysis theory was in good agreement with the experimental values. Further, the finite element model of the eccentric compression of the BFRRAC-filled circular steel tubular stub column could effectively analyze the eccentric mechanical properties.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1999년도 학회창립 10주년 기념 1999년도 가을 학술발표회 논문집
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• pp.529-532
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• 1999

With increasing use of high-strength concrete tied columns in structural engineering, it becomes necessary to examine the applicability of related sections of the current design codes. This experimental study was conducted to investigate the behavior of eccentrically loaded high-strength concrete columns. Column specimens with concrete strength 234, 437, 703kgf/㎠ were tested under monotonically increasing eccentric compression. The test parameters included the longitudinal reinforcement ratio, eccentric distance and concrete compressive strength. The analytical results obtained from the stress-strain relationship and the ACI's equivalent rectangular stress block are compared with experimental test results.

• 한국강구조학회 논문집
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• 제14권5호통권60호
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• pp.567-576
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• 2002

중심 및 2축편심압축에 대한 고강도콘크리트충전 각형강관기둥에 대해 실험 및 해석을 수행하며, 실험변수는 기둥의 좌굴길이대 단면폭의 비 $L_k/D$, 편심의 크기 e, 그리고 편심하중의 각 ${\theta}$이다. 실험을 통하여 2축휨을 받는 고강도콘크리트충전 각형강관기둥의 내력 및 거동을 조사한 결과, 2축편심압축력을 받는 CFT기둥의 실험에 의한 최대내력 및 거동은 해석에 의한 값과 비교적 잘 일치하였다.

• 소성∙가공
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• 제7권5호
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• pp.496-504
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• 1998

The eccentric extrusion and bending process for the forming of the curved rectangular hollow tube is newly developed. Generally the bending process of hollow tube is the secondary process followed by the extrusion process of the hollow tube from the round billet. So many defects such as wrinkling and the difference of wall thickness can be happened during the secondary bending process. In order to avoid the defects the new process named as "the eccentric extrusion and bending process" is suggested and applied to the U-bending of rectangular hollow tube. In this paper the kinematically admissible velocity field between the dies surface and the internal plug boundary surface s developed for the curving velocity. By the using of this curving velocity field the curvature of extruded products can be calculated with the parameters such as eccentricity dies length friction constant aspect ratio.

• Steel and Composite Structures
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• 제48권1호
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• pp.89-102
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• 2023

This study investigates the eccentric performance of concrete-filled steel tubular (CFST) stub columns strengthened with steel tube and sandwiched concrete (STSC) jackets. It was revealed that the STSC jacketing method effectively weakened the cracking of concrete in CFST columns on the convex side and the crash on the concave side. Substantial increases in the eccentric bearing capacities were demonstrated after strengthening. A numerical study was further conducted. The decrease in diameter-to-thickness ratio and increase in strength of outer tube contributed to increase in peak load of all components, whereas the increase in sandwiched concrete strength resulted in load increase on itself and had negligible effects on other components. The parametric study showed the effect of inner concrete strength on columns' bearing capacity was magnified after strengthening, whereas that of inner tube thickness was reduced. Within the parameters investigated, high-strength concrete and high-strength steel can be applied without the concern of early abrupt failure of inner low-strength concrete or steel tube.

• 한국강구조학회 논문집
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• 제14권6호
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• pp.823-834
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• 2002

Steel-Concrete Column은 H형강의 플랜지 사이에 후프를 용접하고 플랜지 사이의 공간에 콘크리트가 채워진 새로운 합성기둥이다. 본 연구에서는 이 새로운 합성 기둥의 구조성능을 평가하기 위하여 단주압축, 휨, 전단실험을 수행하였다. 각 실험별 실험체들을 순철골 실험체와 철골 콘크리트 실험체로 구성하여 Steel-Concrete Column을 구성하는 철골, 내부 콘크리트, 후프의 내력기여도를 평가할 수 있도록 하였다. 실험결과 Steel-Concrete Column은 $\ulcorner$강구조 한계상태 설계 기준$\lrcorner$ 에 의해 계산된 내력값을 충분히 만족하여 구조부재에 적용 가능하다고 판단된다.

• 대한기계학회논문집A
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• 제21권10호
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• pp.1589-1597
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• 1997

The high-velocity impact forging process with eccentric loading condition is analyzed using the explicit time integration finite element method. In order to consider the strain hardening, strain rate hardening and thermal softening effects, which are frequently observed in high-velocity deformation phenomena, the Johnson-Cook constitutive model is applied to model the workpiece. It is assumed that the material response of the dies is elastic in the study. As a result of the eccentric loading simulation, it is found that the increase of the eccentric ratio and the allowable tilting angle cause the decrease of the maximum forging load and the blow efficiency, and it is also found that the forging load and the blow efficiency generated in the high-velocity impact forging process with three-dimensional geometry can be obtained efficiently.

• Structural Engineering and Mechanics
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• 제71권3호
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• pp.211-221
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• 2019

To study the eccentric compression behavior of ultra-high performance fiber reinforced concrete (UHPFRC) columns, six UHPFRC columns and one high-strength concrete (HSC) column were tested. Variation parameters include load eccentricity, volume of steel fibers and stirrup ratio. The crack pattern, failure mode, bearing capacity, and deformation of the specimens were studied. The results showed that the UHPFRC columns had different failure modes. The large eccentric compression failure mode was the longitudinal tensile reinforcements yielded and many horizontal cracks appeared in the tension zone. The small eccentric compression failure mode was the longitudinal compressive reinforcements yielded and vertical cracks appeared in the compressive zone. Because of the bridging effect of steel fibers, the number of cracks significantly increased, and the width of cracks decreased. The load-deflection curves of the UHPFRC columns showed gradually descending without sudden dropping, indicating that the specimens had better deformation. The finite element (FE) analysis was performed to stimulate the damage process of the specimens with monotonic loading. The concrete damaged plasticity (CDP) model was adopted to characterize the behaviour of UHPFRC. The contribution of the UHPFRC tensile strength was considered in the bearing capacity, and the theoretical calculation formulas were derived. The theoretical calculation results were consistent with the test results. This research can provide the experimental and theoretical basis for UHPFRC columns in engineering applications.

• 콘크리트학회논문집
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• 제14권6호
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• pp.864-873
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• 2002

현재의 CFT기둥 구조에 대한 연구는 대부분 강재측 측면에서 접근한 연구와 강관 내부에 충전되는 콘크리트의 충전성 등과 같은 시공적 측면에 대한 연구성과가 주류로 되고 있으며, 콘크리트 측면에서의 연구는 미흡한 실정이다. 이것에 대한 연구를 중심으로 HCFT 기둥이 축력아래에서 단주가 동일한 휨-모멘트를 받을 때의 변형성능(M-ø)에 대하여 해석적으로 수치적인 값을 검토하였다. 그리고, 기본적인 가정을 바탕으로 실험에서 얻은 CFT 단면의 변형성능의 해석에 대하여 모멘트-축력-곡률관계의 해석 프로그램의 개발(C-Language)을 실시하였다. 따라서, 본 연구에서는 폭-두께비(D/t), 세장비(λ), 콘크리트의 종류를 주요변수로 하여 편심하중 아래에서의 강도 600kgf/$\textrm{cm}^2$를 충전한 HCFT 기둥에 대한 내력 및 곡률과 같은 구조적 특성을 고찰하였으며, AISC-LRFD, AIJ, Tokanori Sato의 식을 이용한 내력설계식의 비교분석을 실시하였다. 본 연구에서 검토한 내력 및 곡률은 향후 HCFT 기둥에 대한 내력설계식의 제안 및 해석에 유용하게 적용될 수 있을 것으로 사료된다.