• 한국공간구조학회논문집
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• 제7권3호
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• pp.79-86
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• 2007

최근, 건설되어지는 강구조물들의 장경간화 및 고층화로 인하여 고강도강재의 적용이 점차 요구되고 있다. 고강도강재는 적용구조물들을 공간 및 두께들 감소시킴으로써 외관성 및 경제성을 증가시킬 수 있는 장점이 있다. 이러한 고강도 강재의 적용을 위해서는 좌굴에 대한 기준이 필요하나 현재 국내의 경우 이러한 좌굴에 관한 연구가 미흡하다. 이에 본 연구에서는 3차원 탄소성 유한변위 프로그램을 이용하여 고강도 박스단면 트러스 부재의 좌굴거동에 대한 해석적 연구를 수행하였다. 고강도강재를 적용한 박스단면 트러스부재의 허용 압축응력에 대한 기준을 제안하였으며 그 적용성을 확인하였다. 그리고 고강도 트러스 부재의 설계에도 적용할 수 있음을 명확히 하였다.

• 한국공간구조학회논문집
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• 제7권6호
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• pp.69-74
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• 2007

교량의 교각과 같은 원형기둥구조물의 성능과 강도을 향상시키기 위해 최근 콘크리트 충전강관(CFT: concrete-filled steel tube)의 적용이 점차 증가하고 있다. 이러한 콘크리트 충전강관 구조물의 정확한 소성설계를 위해서는 사용된 재료인 강재 및 콘크리트의 대변형 거동을 구현할 수 있는 소성모델이 필요하다. 본 연구에서는 사용강재의 실험을 통하여 제안된 소성모델을 적용한 탄소성 대변형 해석을 개발하였으며 콘크리트 충전강관 기둥 해석과 실험 결과에 비교하여 그 정도 및 타당성을 검증하였다. 그리고 개발된 프로그램을 이용하여 콘크리트 충전강관 기둥의 초기처짐이 극한장도에 미치는 영향 및 상관관계를 명확히 파악하였다.

• Steel and Composite Structures
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• 제22권6호
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• pp.1487-1505
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• 2016

This paper presents the results of an experimental study on the behavior of a new type of composite FRP-concrete-steel member subjected to bi-axial eccentric loading. This new type of composite member is in the form of concrete-filled square steel tube slender columns with inner CFRP (carbon fiber-reinforced polymer) circular tube, composed of an inner CFRP tube and an outer steel tube with concrete filled in the two tubes. Tests on twenty-six specimens of high strength concrete-filled square steel tube columns with inner CFRP circular tube columns (HCFST-CFRP) were carried out. The parameters changed in the experiments include the slenderness ratio, eccentric ratio, concrete strength, steel ratio and CFRP ratio. The experimental results showed that the failure mode of HCFST-CFRP was similar to that of HCFST, and the specimens failed by local buckling because of the increase of lateral deflection. The steel tube and the CFRP worked together well before failure under bi-axial eccentric loading. Ductility of HCFST-CFRP was better than that of HCFST. The ultimate bearing capacity of test specimen was calculated with simplified formula, which agreed well with test results, and the simplified formula can be used to calculate the bearing capacity of HCFSTF within the parameters of this test.

• 한국강구조학회 논문집
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• 제17권5호통권78호
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• pp.605-615
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• 2005

수평하중을 받는 콘크리트충전 각형강관 기둥의 축력과 변형능력의 관계를 조사하기 위하여 실험 및 해석적 연구를 수행하였다. 36개 기둥으로 구성된 실험 시리즈는 일정 축하중과 수평하중 하에서 반복실험을 실시하였다. 반복 수평하중을 받는 기둥이 저항할 수 있는 축하중을 보증내력 한계축력이라고 규정하였으며, 해석 모델은 수평하중을 받는 캔틸레버 기둥을 모델화하였다. 반복 횡하중을 받는 기둥의 축하중을 누적보증내력 한계축력이라고 정의하였다. 본 연구의 목적은 주어진 동일부재각에 부합하는 축력과 수평하중을 받는 콘크리트 충전강관 기둥의 보증내력 한계축력을 연구하기 위한 것이며, 두 번째는 콘크리트 충전강관 기둥의 누적보증내력 한계축력과 보증내력 한계축력의 비교가 본 연구의 목적이다.

• Computers and Concrete
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• 제25권2호
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• pp.95-109
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• 2020

This paper aims to analytically study the effect of loading conditions and confinement type on the mechanical properties of the concrete-steel composite columns under axial compressive loading. The axial loading is applied to the composite columns in the two ways; only on the concrete core, and on the concrete core and steel tube simultaneously, which are called steel tube-confined concrete (STCC) and concrete-filled steel tube (CFST) columns, respectively. In addition, the confinement is investigated in the three types of passive, short-term active and long-term active confinement. Nonlinear finite element 3D models for analyzing these columns are developed using the ABAQUS program, and then these models are verified with respect to the recent experimental results reported by the authors on the STCC and CFST columns experiencing active and passive confinements. Axial and lateral stress-strain curves as well as the failure mode for qualitative verification, and compressive strength for quantitative verification are considered. It is found that there is a good consistency between the finite element analysis results and the experimental ones. In addition, a parametric study is performed to evaluate the effect of axial loading type, prestressing ratio, concrete compressive strength and steel tube diameter-to-wall thickness ratio on the compressive behavior of the composite columns. Finally, the compressive strength results of CFST specimens obtained via the finite element analysis are compared with the values specified by the international codes and standards including EC4, CSA, ACI-318, and AISC, with the results showing that ACI-318 and AISC underestimate the compressive strength of the composite columns, while EC4 and CSA codes present overestimated values.

• Steel and Composite Structures
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• 제22권1호
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• pp.63-77
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• 2016

Top-down construction is a construction technique in which pit excavation and structure construction are conducted simultaneously. Reducing construction time and minimizing noise and vibration which affect neighboring structures, the technique is widely employed in constructing downtown structures. While H-steel columns have been commonly used as core columns, concrete filled steel tube (CFT) columns are at the center of attention because the latter have less axial directionality and greater cross-sectional efficiency than the former. When compared with circular CFT columns, square CFT columns are more easily connected to the floor structure and the area of percussion rotary drilling (PRD) is smaller. For this reason, square CFT columns are used as core columns of concrete encased and filled square (CET) columns in underground floors. However, studies on the structural behavior and concrete stress transfer of CET columns have not been conducted. Since concrete is cast according to construction sequence, checking the stress of concrete inside the core columns and the stress of covering concrete is essential. This paper presents the results of structural tests and analyses conducted to evaluate the usability and safety of CET columns in top-down construction where CFT columns are used as core columns. Parameters in the tests are loading condition, concrete strength and covering depth. The compressive load capacity and failure behavior of specimens are evaluated. In addition, 2 cases of field application of CET columns in underground floors are analyzed.

• Steel and Composite Structures
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• 제15권6호
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• pp.679-703
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• 2013

This paper presents experimental investigations of the fundamental behavior of concrete filled steel tube (CFT) beam-columns under fire loading. A total of thirteen specimens were tested to determine the axial force-moment-curvature-temperature behavior of CFT beam-columns. The experimental approach involved the use of: (a) innovative heating and control equipment to apply thermal loading and (b) digital image correlation with close-range photogrammetry to measure the deformations (e.g., curvature) of the heated region. Each specimen was sequentially subjected to: (i) constant axial loading; (ii) thermal loading in the expected plastic hinge region following the ASTM E119 temperature-time T-t curve; and (iii) monotonically increasing flexural loading. The effects of various parameters on the strength and stiffness of CFT beam-columns were evaluated. The parameters considered were the steel tube width, width-tothickness ratio, concrete strength, maximum surface temperature of the steel tube, and the axial load level on the composite CFT section. The experimental results provide knowledge of the fundamental behavior of composite CFT beam-columns, and can be used to calibrate analytical models or macro finite element models developed for predicting behavior of CFT members and frames under fire loading.

• Structural Engineering and Mechanics
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• 제46권3호
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• pp.323-335
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• 2013

This work aims to study the effect of stiffener ties in the behavior of intermediate length open section Cold-Formed Steel (CFS) Columns under axial compression. A comparative study on the behaviour and strength of Cold Formed Steel Columns by changing the direction of projection of lips (i.e., inwards or outwards) are also done. In this work two types of sections were considered Type-I section with lip projecting outwards (hat) and Type-II section with lip projecting inwards (channel). The length of the columns is predicted by performing elastic buckling analysis using CUFSM software. The theoretical analysis is performed using DSM - S100;2007, AS/NZ: 4600-2005 and IS: 801-1975. The compression tests are carried out in a 400 kN loading frame with hinged-hinged end condition. The non-linear numerical analysis is performed using Finite Element software ANSYS 12.0 to simulate the experimental results. Extensive parametric study is carried out by varying the width and spacing of the stiffener ties. The results are compared; the effects of stiffener ties on behaviour and load carrying capacity on both types of columns are discussed.

• Structural Engineering and Mechanics
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• 제62권4호
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• pp.417-430
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• 2017

Ultra high performance concrete (UHPC) has aroused interest around the world owing to superior mechanical and durability properties over conventional concrete. However, the application of UHPC in practice poses difficulties due to its inherent brittleness. UHPC filled in steel tube columns (UHPC-FSTCs) are capable of restricting the brittle failure of non-reinforced UHPC columns and forming a high performance member with enhancement of strength and ductility. Currently, research on UHPC-FSTCs remains very limited and there is relatively little information about the mechanical behavior of these columns. Therefore, this study presents a review of past experimental studies to have a deeper insight into the compressive behavior of UHPC-FSTCs under axial loading on entire section and on concrete core. Based on the test results obtained from Schneider (2006) and Xiong (2012), an analysis was conducted to investigate the influence of the confinement index (${\xi}$) and diameter to steel tube thickness ratio (D/t) on the strength and the ductility in short circular UHPC-FSTCs. Furthermore, the appropriateness of current design codes including EC4, AISC, AIJ and previous analytical models for estimating the ultimate loads of composite columns was also examined by the comparison between the predictions and the test results. Finally, simplified formulae for predicting the ultimate loads in two types of loading pattern were proposed and verified.

• Steel and Composite Structures
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• 제11권4호
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• pp.307-324
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• 2011

With the increasing use of concrete-filled steel tubes (CFST) as structural members, there is a growing need to provide suitable measures for possible strengthening or repair of these kinds of structural elements. Fibre reinforced polymer (FRP) jacketing is a recent method and is particularly attractive in which it does not significantly increase the section size, and is relatively easy to install. Thus, it can be used to enhance strength and/or ductility of CFST members. Very little information is available on the performance of FRP-strengthened CFST members under fire conditions. This paper is an attempt to study the fire performance of CFST columns strengthened by FRP. The results of fire endurance tests on FRP-strengthened circular CFST columns are presented. Failure modes of the specimens after exposure to fire, temperatures in the cross section, axial deformation and fire resistance of the composite columns are analysed. It is demonstrated that the required fire endurance can be achieved if the strengthened composite columns are appropriately designed.