• Steel and Composite Structures
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• 제27권2호
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• pp.193-200
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• 2018

This paper presents an experimental work for short circular steel tube columns filled with normal concrete (NAC), recycled aggregate concrete (RAC), and RAC with silica fume and steel fiber. Ten specimens were tested under axial compression to research the effect of silica fume and steel fiber volume percentage on the behavior of recycled aggregate concrete-filled steel tube columns (RACFST). The failure modes, ultimate loads and axial load- strain relationships are presented. The test results indicate that silica fume and steel fiber would not change the failure mode of the RACFST column, but can increase the mechanical performances of the RACFST column because of the filling effect and pozzolanic action of silica fume and the confinement effect of steel fiber. The ultimate load, ductility and energy dissipation capacity of RACFST columns can exceed that of corresponding natural aggregate concrete-filled steel tube (NACFST) column. Design formulas EC4 for the load capacity NACFST and RACFST columns are proposed, and the predictions agree well with the experimental results from this study.

• Steel and Composite Structures
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• 제34권6호
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• pp.803-818
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• 2020

Semi-rigid connections with blind bolts could solve the difficulty that traditional high strength bolts were unavailable to splice a steel/composite beam to a closed section column. However, insufficient investigations have focused on the performance of semi-rigid connection to square concrete filled double-skin steel tubular (CFDST) columns. In this paper, a component model was developed to evaluate the mechanical behavior of semi-rigid composite connections to CFDST columns considering the stiffness and strength of column face in compression and column web in shear which were determined by the load transfer mechanism and superstition method. Then, experimental investigations on blind bolted composite joints to square CFDST columns were conducted to validate the accuracy of the component model. Dominant failure modes of the connections were analyzed and this type of joint behaved semi-rigid manner. More importantly, strain responses of CFDST column web and tubes verified that stiffness and strength of column face in compression and column web in shear significantly affected the connection mechanical behavior owing to the hollow part of the cross-section for CFDST column. The experimental and analytical results showed that the CFDST column to steel-concrete composite beam semi-rigid joints could be employed for the assembled structures in high intensity seismic regions.

• Steel and Composite Structures
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• 제32권5호
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• pp.583-594
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• 2019

In recent years, composite concrete-filled steel tubular (CFST) members have been widely utilized in framed building structures like beams, columns, and beam-columns since they have significant advantages such as reducing construction time, improving the seismic performance, and possessing high ductility, strength, and energy absorbing capacity. This paper presents a new composite joint - the composite CFST beam-column joint in which the CFST member is used as the beam. The main components of the proposed composite joint are steel H-beams, CFST beams welded with the steel H-column, and a reinforced concrete slab. The steel H-beams and CFST beams are connected with the concrete slab using shear connectors to ensure composite action between them. The structural performance of the proposed composite joint was evaluated through an experimental investigation. A three-dimensional (3D) finite element (FE) model was developed to simulate this composite joint using the ABAQUS/Explicit software, and the accuracy of the FE model was verified with the relevant experimental results. In addition, a number of parametric studies were made to examine the effects of the steel box beam thickness, concrete compressive strength, steel yield strength, and reinforcement ratio in the concrete slab on the proposed joint performance.

• Steel and Composite Structures
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• 제32권1호
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• pp.141-156
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• 2019

This paper presents the flexural behaviour of stainless steel beam-to-tubular column joints with extended endplates subjected to static loading. Moment-rotation relationships were investigated numerically by using Abaqus software with geometric and material nonlinearity considered. The prediction of damages among components was achieved through ductile damage models, and the influence of initial geometric imperfections and residual stresses was evaluated in large fabricated stainless steel joints involving hollow columns and concrete-filled columns. Parametric analysis was subsequently conducted to assess critical factors that could affect the flexural performance significantly in terms of the initial stiffness and moment resistance. A comparison between codes of practice and numerical results was thereafter made, and design recommendations were proposed for further applications. Results suggest that the finite element model can predict the structural behaviour reasonably well with the component damage consistent with test outcomes. Initial geometric imperfections and residual stresses are shown to have little effect on the moment-rotation responses. A series of parameters that can influence the joint behaviour remarkably include the strain-hardening exponents, stainless steel strength, diameter of bolts, thickness of endplates, position of bolts, section of beams and columns. AS/NZS 2327 is more reliable to predict the joint performance regarding the initial stiffness and moment capacity compared to EN 1993-1-8.

• 한국강구조학회 논문집
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• 제26권1호
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• pp.31-42
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• 2014

본 연구에서는 콘크리트충전 각형강관에 구조용 피복콘크리트를 적용한 합성기둥에 대하여 연구하였다. 1/3~1/2 축소모델의 편심 압축실험체 4개와 중심압축실험체 1개를 제작하여 압축실험을 수행하였다. 실험 변수는 피복콘크리트의 강섬유 첨가여부, 편심거리, 기둥 길이, 그리고 횡보강 상세이다. 일부 실험체에서 최대강도 도달 후 피복콘크리트의 탈락으로 인한 강도저하가 발생하였으나 모든 실험체는 현행 설계기준(KBC 2009)에 의한 휨 압축 강도 및 공칭 압축강도를 초과하는 하중재하능력을 보였다.

• Steel and Composite Structures
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• 제44권1호
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• pp.1-15
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• 2022

The weld quality has always been an important factor affecting the development of exposed CFT column-base joint. In this paper, a new type of exposed RCFST column-base joint is proposed, in which the high strength steel bars (USD 685) are set through the column and reinforced concrete foundation without any base plate and anchor bolts. Three specimens, the varying axial force ratio (0, 0.25 and 0.5), were tested under cyclic loadings. In addition, the bending moment capacity, energy dissipation capacity and deformation capacity of column-base joints were clarified. The experimental results indicated that the axial force ratio increases the stiffness and the bending moment and improves the energy dissipation capacity of column-base joints. This is because a large axial force can limit the slip between steel tubular and infilled concrete effectively. The specimens show stable hysteresis behavior.

• 한국구조물진단유지관리공학회 논문집
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• 제5권1호
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• pp.161-168
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• 2001

The use of composite members to improve the compressive strength of steel structure is a common practice these days and its efficiency has already been proved by several researches and experiments. The result of concrete filled circular tubular(CFCT) stub column tests is introduced in this paper. The main parameter of this test is the ratio of diameter to thickness of circular hollow section. From the test results, the effect of concrete filled in steel tube on the ultimate strength, the deformation capacity and initial stiffness are discussed. The purpose of this paper is to investigate the effect of various parameters and evaluate the compressive strength of confined concrete. It would contribute to a better understanding of CFT structure, further laboratory experimentations are needed for better accurate estimation on its effect.

• Structural Engineering and Mechanics
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• 제24권4호
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• pp.463-478
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• 2006

The design of structural frameworks for buildings is constantly evolving and is dependent on regional issues such as loading and constructability. One of the most promising recent developments for low to medium rise construction in terms of efficiency of construction, robustness and aesthetic appearance utilises concrete-filled steel tubular sections as the columns in a moment-resisting frame. These are coupled to rigid or semi-rigid connections to composite steel-concrete beams. This paper includes the results of a pilot experimental programme leading towards the development of economical, reliable connections that are easily constructed for this type of frame. The connections must provide the requisite strength, stiffness and ductility to suit gravity loading conditions as well as gravity combined with the governing lateral wind or earthquake loading. The aim is to develop connections that are stiffer, less expensive and easier to construct than those in current use. A proposed fabricated T-stub connection is to be used to connect the beam flanges and the column. These T-stubs are connected to the column using "blind bolts" with extensions, allowing installation from the outside of the tube. In general, the use of the extensions results in a dramatic increase in the strength and stiffness of the T-stub to column connection in tension, since the load is shared between membrane action in the tube wall and the anchorage of the bolts through the extensions into the concrete.

• 한국강구조학회 논문집
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• 제23권3호
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• pp.317-326
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• 2011

최근 CFT(Concrete Filled Steel Tube) 부재는 뛰어난 구조성능으로 인하여 그 사용범위가 확대되고 있다. 본 연구에서는 축력과 반복수평력을 받는 콘크리트 충전 내진 각형강관 기둥의 연성을 평가하는 실험을 수행하였다. 내진 각형강관은 SN400B 후판재를 냉간 프레스 성형하여 2개의 ㄷ자로 절곡한 후 기둥 폭의 중앙에서 2-seam 용접하는 방식으로 제작하였다. 강관의 폭두께비, 축력비, 가력방법을 변수로 총 8개의 실험체를 제작하여 실험을 수행하였고, 축하중과 반복수평력을 가력하기 위하여 2대의 액츄에이터가 사용되었다. 실험결과를 통해 기둥의 휨내력, 변형능력 및 에너지소산능력을 평가하였으며, 반복수평력에 대한 기둥의 연성거동 또한 평가되었다.

• Steel and Composite Structures
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• 제20권1호
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• pp.1-20
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• 2016

The strength and stiffness of the steel beams to concrete-filled tubular columns connections are significantly reduced if the thick-walled components are used. However, the thick-walled tubes used for columns can largely reduce the demand for space and increase the strength-to-weight ratio. This paper describes the cyclic performance of extended through-diaphragm connections between steel beams and thick-walled concrete-filled tubular columns improved with fillets around the diaphragm corners. Test on one full-scale connection was conducted to assess the seismic behavior of the connection in terms of strength, stiffness, ductility, deformation, energy dissipation, and strain distribution. It is shown that the fillets and extended through-diaphragm can alleviate the stress concentration in the connection and thus improve the seismic performance. The test results demonstrate that the through-diaphragm connections with thick-walled concrete-filled tubular columns can offer sufficient energy dissipation capacity and ductility appropriate for its potential application in seismic design.