• 한국강구조학회 논문집
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• 제22권6호
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• pp.523-532
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• 2010

콘크리트가 충전된 각형강관기둥(이하, 각형 CFT기둥)은 높은 내화성능과 하중저항능력을 보유하고 있지만, CFT기둥의 외부에 내화피복을 함으로써 기둥의 내화성능을 향상시킬 필요가 있다. 본 연구는 내화 피복된 각형 CFT기둥의 온도분포에 대한 실험결과이다. 실험을 위하여 특수 제작된 전기로를 이용하여 축소모형 시험체의 재하가열실험을 수행하였다. 축하중을 받는 내화 피복된 각형 CFT기둥의 온도 분포 특성을 파악하기 위하여 내화피복의 종류와 두께, 강관의 두께 및 가열시간 등을 변수로 설정하였다. 실험결과 전기로의 온도에 따른 시험체별 온도분포와 콘크리트와 강재의 온도분포 특성을 파악하였다. 또한 시험체의 온도변화에 따른 축변위와 국부좌굴 등의 거동을 파악하였다.

• 한국강구조학회 논문집
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• 제24권1호
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• pp.81-89
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• 2012

콘크리트 충전강관 기둥은 내부의 콘크리트에 의해 축열효과로 인해 철골기둥에 비해 내화성능이 우수하며, 기둥 단면 내 철근 및 강관을 보강하여 구조적내력 및 내화성능 향상연구가 이루어져 오고 있다. 실제로 보강된 CFT기둥은 고축력을 요구하는 기둥부재로 사용 빈도 수가 증가되고 있는 추세이다. 이러한 상황에서 CFT기둥을 사용한 건축물에 화재가 발생하여 손상을 입게 되었을 경우 성능 저하정도를 정밀하게 측정할 수 있는 기법이 필요하다. 본 연구에서는 화재 발생시 CFT기둥에 대한 내부 온도 분포를 평가 하고, 단면내부의 온도분포에 따라 내부 충전콘크리트와 보강재의 내력 저하 정도를 파악하여 CFT기둥의 전체적인 잔존강도를 평가하고자 한다.

• 한국강구조학회 논문집
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• 제9권1호통권30호
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• pp.121-128
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• 1997

It has been reported by the existing papers that the ultimate load capacity and energy absorption capacity of the CFST column are considerably higher than those resulting from a simple addition of the capacities of the concrete and the steel tube. It is normally believed that the confined effect for the infilled concrete due to the hoop tension of steel at the parameter of cross sections can remarkably improve the ductility and energy absorption capacities of the CFST columns. This paper provides the results of a study on the load-carrying capacities and energy absorption capacities of the CFST columns, a numerical analysis method, i. e. N-M interaction curves and Moment curvature relationships. The numerical approaches are verified by comparing with the existing test results and the circular and square steel tube sections are selected to clarify the amount of confinement effects to improve the ultimate deformable capacity(a ultimate strain value) of the infilled concrete. Then, an adequate value of the ultimate strain of the infilled concrete and an equation of the ultimate capacity of the CFST column are suggested.

• Steel and Composite Structures
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• 제34권1호
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• pp.123-139
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• 2020

The tube outward local buckling of Concrete-Filled Steel Tube (CFST) beam under high compression stress is still considered a critical problem, especially for steel tubes with a slender section compared to semi-compact and compact sections. In this study, the flexural performance of stiffened slender cold-formed square tube beams filled with normal concrete was investigated. Fourteen (14) simply supported CFST specimens were tested under static bending loads, stiffened with different shapes and numbers of steel stiffeners that were provided at the inner sides of the tubes. Additional finite element (FE) CFST models were developed to further investigate the influence of using internal stiffeners with varied thickness. The results of tests and FE analyses indicated that the onset of local buckling, that occurs at the top half of the stiffened CFST beam's cross-section at mid-span was substantially restricted to a smaller region. Generally, it was also observed that, due to increased steel area provided by the stiffeners, the bending capacity, flexural stiffness and energy absorption index of the stiffened beams were significantly improved. The average bending capacity and the initial flexural stiffness of the stiffened specimens for the various shapes, single stiffener situations have increased of about 25% and 39%, respectively. These improvements went up to 45% and 60%, for the double stiffeners situations. Moreover, the bending capacity and the flexural stiffness values obtained from the experimental tests and FE analyses validated well with the values computed from equations of the existing standards.

• Steel and Composite Structures
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• 제38권6호
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• pp.617-635
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• 2021

This paper numerically investigated the behavior of built-up square concrete-filled steel tubular (CFST) columns under combined preload and axial compression. The finite element (FE) models of target columns were verified in terms of failure mode, axial load-deformation curve and ultimate strength. A full-range analysis on the axial load-deformation response as well as the interaction behavior was conducted to reveal the composite mechanism. The parametric study was performed to investigate the influences of material strengths and geometric sizes. Subsequently, influence of construction preload on the full-range behavior and confinement effect was investigated. Numerical results indicate that the axial load-deformation curve can be divided into four working stages where the contact pressure of curling rib arc gradually disappears as the steel tube buckles; increasing width-to-thickness (B/t) ratio can enhance the strength enhancement index (e.g., an increment of 1.88% from B/t=40 to B/t=100), though ultimate strength and ductility are decreased; stiffener length and lip inclination angle display a slight influence on strength enhancement index and ductility; construction preload can degrade the plastic deformation capacity and postpone the origin appearance of contact pressure, thus making a decrease of 14.81%~27.23% in ductility. Finally, a revised equation for determining strain εscy corresponding to ultimate strength was proposed to evaluate the plastic deformation capacity of built-up square CFST columns.

• Structural Engineering and Mechanics
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• 제69권6호
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• pp.627-635
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• 2019

In order to study the axial compression performance of sand-lightweight concrete-filled steel tube (SLCFST) stub columns, three circular SLCFST (C-SLCFST) stub column specimens and three SLCFST square (S-SLCFST) stub column specimens were fabricated and static monotonic axial compression performance testing was carried out, using the volume ratio between river sand and ceramic sand in sand-lightweight concrete (SLC) as a varying parameter. The stress process and failure mode of the specimens were observed, stress-strain curves were obtained and analysed for the specimens, and the ultimate bearing capacity of SLCFST stub column specimens was calculated based on unified strength theory, limit equilibrium theory and superposition theory. The results show that the outer steel tubes of SLCFST stub columns buckled outward, core SLC was crushed, and the damage to the upper parts of the S-SLCFST stub columns was more serious than for C-SLCFST stub columns. Three stages can be identified in the stress-strain curves of SLCFST stub columns: an elastic stage, an elastic-plastic stage and a plastic stage. It is suggested that AIJ-1997, CECS 159:2004 or AIJ-1997, based on superposition theory, can be used to design the ultimate bearing capacity under axial compression for C-SLCFST and S-SLCFST stub columns; for varying replacement ratios of natural river sand, the calculated stress-strain curves for SLCFST stub columns under axial compression show good fitting to the test measure curves.

• 한국강구조학회 논문집
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• 제25권1호
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• pp.71-80
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• 2013

구조, 시공 및 내화측면에서 우수한 콘크리트충전강관(CFT)부재에 대해서 구성재료의 강도가 높은 경우 즉, 콘크리트 압축강도가 100MPa 이상이면서 강관의 항복강도가 650MPa 이상인 경우에 대한 내화성능 평가실험 및 해석적 연구는 미비한 실정이다. 본 연구에서는 이러한 부재에 대해서 내화성능 거동을 파악하고자 ${\Box}-400{\times}400{\times}15$, 부재길이 3,000mm인 실물대 중심재하 내화실험을 행하였다. 실험변수는 중심축력을 5,000kN과 2,500kN로 하였다. 실험결과, 고강도 콘크리트의 폭렬 및 콘크리트 내부 균열에 의하여 축하중이 클수록 조기에 내력을 상실하였다. 또한, 유한차분법과 변형률적합조건을 이용한 비정상온도해석 및 응력해석을 수행하였으며, 고강도 재료모델은 Eurocode모델을 이용하였다. 해석모델은 시간-축변위 관계를 합리적으로 예측할 수 있었다.

• 한국공간구조학회논문집
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• 제12권4호
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• pp.81-90
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• 2012

The concrete-filled tube (CFT) column has the excellent structural performance. But it is difficult to connect with column and beam because of closed section. Its Solution, 2 members of ㄷchennel in which Internal diaphragm is installed were welded beforehand and the method of making Rectangular Steel Tube was proposed. According to upside and downside junction shape, Internal diaphragm suggested as symmetric specimen and asymmetric specimen. The upper and lower diaphragm of the Symmetric specimen used the same horizontal and The upper diaphragm of the Asymmetric specimen used the horizontal plate and the lower diaphragm used the vertically plate. In this research, 4 T-shape column to beam steps connections were tested with cyclic loading experiment in order to evaluate the structural capability of the offered connection. Symmetric specimens be a failure in 0.03rad from beam flange. And Asymmetric specimens be a failure in 0.05rad from column interface. The comparison results of All specimens shown similar to energy absorption capacity in 0.02rad.

• Steel and Composite Structures
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• 제51권6호
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• pp.661-678
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• 2024

The utilization of geopolymer recycled aggregate concrete (GRAC) as the infilled core of the concrete-filled steel tubular (CFST) columns provides superior economic and environmental benefits. However, limited research exists within the field of geopolymer recycled aggregate concrete considered a green and sustainable material, in addition to the limitation of the design guidelines to predict the behavior of such an innovative new material combination. Moreover, the behavior of high-strength concrete is different from the normal-strength one, especially when there is another material of high-strength properties, such as the steel tube. This paper aims to investigate the behavior of the axially loaded square high-strength GRACFST columns through the nonlinear finite element analysis (NLFEA). A total of thirty-two specimens were simulated using ABAQUS/Standard software with three main variables: recycled aggregate replacement ratio (0, 30, and 50) %, width-to-thickness ratios (52.0, 32.0, 23.4, and 18.7), and length-to-width ratio (3, 5, 9, and 12). During the analysis, the response in terms of the axial load versus the longitudinal strain was recorded and plotted. In addition, various mechanical properties were calculated and analyzed. In view of the results, it has been demonstrated that the mechanical properties of high-strength GRACFST columns such as ultimate load-bearing capacity, compressive stiffness, energy absorption capacity, and ductility increase with the increase of the steel tube thickness owing to the improvement of the confinement effect of the steel tube. In contrast, the incorporation of the recycled aggregate adversely affected the mentioned properties except the ductility, while the increase of the recycled aggregate replacement ratio improved the column's ductility. Moreover, it has been found that the increase in the length-to-width ratio significantly reduced both the failure strain and the energy absorption capacity. Finally, the obtained NLFEA results of the ultimate load-bearing capacity were compared with the corresponding predicted capacities by numerous codes. It has been concluded that AISC, ACI, and EC give conservative predictions for the ultimate load-bearing capacity since the confinement effect was not considered by these codes.

• 한국강구조학회 논문집
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• 제12권4호통권47호
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• pp.387-395
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• 2000

본 연구는 콘크리트충전 각형강관(CFT) 기둥의 강도와 변형능력의 평가 및 내진성능에 대한 기초 자료의 제시를 목적으로 한다. 실험체는 초고층 건물의 최하단기둥의 응력분포를 가정하여 켄틸레버형 기둥으로 하고, 총 18개의 실험체가 일정 축력과 반복 횡하중 하에서 실험되었다. 본 실험에 적용된 주요변수는 강관의 폭/두께 비, 세장비 (LO/D), 그리고 축력비이다. 각 변수가 기둥의 강도, 변형능력, 그리고 에너지 흡수능력에 미치는 영향이 기술되었고, 각국 규준식과 실험결과를 비교하였다. 분석결과, 피복형 한국강구조학회 규준은 합성 단면적과 탄성계수를 AIJ와 AISC-LRFD 수준으로 수정한다면, 충전형에도 적용가능 할 것으로 판단된다. 마지막으로, 구속효과를 고려하여 단면의 소성해석을 통하여 구한 B. Kato의 CFT 기둥의 휨내력 제안식은 실험결과와 좋은 대응을 나타내고 있다.