• Steel and Composite Structures
• /
• 제12권6호
• /
• pp.523-540
• /
• 2012

It was clear from the former researches on reinforced concrete filled tubular steel (RCFT) structures that RCFT structures have different performance than concrete filled steel tubular (CFT) structures. However, despite of that, load-sharing ratio of RCFT is evaluating by the formula and range of CFT given by JSCE. Therefore, the aim of this investigation is to study the load-sharing ratio of RCFT columns subjected to axial compressive load by performing numerical simulations of RCFT columns with the nonlinear finite element analysis (FEA) program - ADINA. To achieve this goal, firstly proper material constitutive models for concrete, steel tube and reinforcement are proposed. Then axial compression tests of concrete, RC, CFT, and RCFT columns are carried out to verify proposed material constitutive models. Finally, by the plenty of numerical analysis with small-sized and big-sized columns, load-sharing ratio of RCFT columns was studied, the evaluation formulas and range were proposed, application of the formula was demonstrated, and following conclusions were drawn: The FEA model introduced in this paper can be applied to nonlinear analysis of RCFT columns with reliable results; the load-sharing ratio evaluation formula and range of CFT should not be applied to RCFT; The lower limit for the range of load-sharing ratio of RCFT can be smaller than that of CFT; the proposed formulas for load-sharing ratio of RCFT have practical mean in design of RCFT columns.

• Steel and Composite Structures
• /
• 제11권5호
• /
• pp.391-402
• /
• 2011

It is clear from the former researches on reinforced concrete filled steel tubular (RCFT) structures that RCFT structures have higher strength and deformation capacity than concrete filled steel tubular (CFT) structures. However, in the case of actual applications to large-scaled structures, the thin-walled steel tube must be used from the view point of economic condition. Therefore, in this study, compression tests of RCFT columns which were made by thin-walled steel tube or small load-sharing ratio in cooperation with high strength concrete were carried out, meanwhile corresponding tests of CFT, reinforced concrete (RC), pure concrete and steel tube columns were done to compare with RCFT. By the a series of comparison and analysis, characteristics of RCFT columns were clarified, and following conclusions were drawn: RCFT structures can effectively avoided from brittle failure by the using of reinforcement while CFT structures are damaged due to the brittle failure; with RCFT structures, excellent bearing capacity can be achieved in plastic zone by combining the thin-walled steel tube with high strength concrete and reinforcement. The smaller load-sharing ratio can made the reinforcement play full role; Combination of thin-walled steel tube with high strength concrete and reinforcement is effective way to construct large-scaled structures.

• Steel and Composite Structures
• /
• 제16권6호
• /
• pp.639-655
• /
• 2014

The mechanical characteristic of reinforced concrete filled steel tubular (RCFT) structures are differed from that of concrete filled tubular steel (CFT) structures because the reinforcement in RCFT largely affects the performance of core concrete such as ductility, strength and toughness, and hence the performance of RCFT should be evaluated differently from CFT. To examine the effect axial reinforcement on bending performance, an investigation on RCFT beams with varying levels of axial reinforcement is performed by the means of numerical parametric study. According to the numerical simulation results with 13 different ratios of axial reinforcement, it is concluded that the reinforcement has obvious effect on bending capacity, and the neutral axis of RCFT is different from CFT, and an evaluation equation in which the effect of axial reinforcement is considered for ultimate bending strength of RCFT is proposed.

• 한국HCI학회:학술대회논문집
• /
• 한국HCI학회 2008년도 학술대회 2부
• /
• pp.507-512
• /
• 2008

본 연구는 경도인지장애(MCI)환자의 가상환경(VE)내 길찾기 학습능력을 측정하였으며, 전통 신경심리검사를 이용하여 길찾기 능력을 구성하는 인지기능에 대해 조사하였다. 피험자는 정상노인집단(N=27)과 MCI 환자집단(N=22)으로 구성되었다. 피험자는 간이정신집단검사, 시각 기억력을 측정하는 Rey Complex Figure Test(RCFT), 시각적 보존력을 측정하는 Benton Visual Retention(BVRT), 주의력을 측정하는 Trail-Making Test(TMT; A형과 B형), 성인용 웩슬러 지능검사의 하위검사인 숫자외우기(바로/거꾸로), 및 집행기능 및 기억력을 측정하는 2차원공간에서의 미로학습검사 Groton Maze Learning Test(GMLT)(12회기)를 마친 후, 가상현실(VE) 내 길찾기과제(6회기)를 수행하였다. 그 결과, VE 길찾기 과제에 대하여 유의미한 집단효과가 나타났다. 즉, MCI집단의 길찾기 수행이 정상노인집단의 길찾기 수행보다 떨어지는 결과가 발견되었다. 집단과 회기간 상호작용 및 유의미한 회기효과는 나타나지 않았다. GMLT에서는 유의미한 상호작용, 집단효과, 및 회기효과가 나타나지 않았다. 신경심리검사에서는 RCFT와 BVRT에서 유의미한 집단간 차이가 발견되었다. 또한, VE과제는 RCFT, BVRT, 그리고 GMLT와 상관이 있었으며, 이를 기반으로한 회기분석 실시 결과 RCFT와 BVRT는 가상환경 내 길찾기 행동에 대한 45%의 설명력을 지니고 있었다. 결론적으로, 본 연구결과는 MCI환자의 길찾기 능력이 정상인에 비하여 떨어지며, MCI환자의 시공간기억기능 결함으로 이와 같은 길찾기 능력저하를 설명할 수 있음을 함의한다.

• Structural Engineering and Mechanics
• /
• 제56권5호
• /
• pp.727-743
• /
• 2015

According to former studies, the mechanical properties of reinforced concrete filled tubular steel (RCFT) columns differed greatly from that of concrete filled steel tubular (CFT) columns because of interaction of inserted reinforcement in RCFT. Employing an experiment-based verification policy, a general FE nonlinear analysis model was developed to analyze the mechanical behavior and failure mechanism of RCFT columns under uniaxial compression. The reasonable stress-strain relationships were suggested for confined concrete, reinforcements and steel tube in the model. The mechanism for shear failure of concrete core was found out in the numerical simulation, and a none-conventional method and equation for evaluating the confinement effect of RCFT were proposed.

• 한국강구조학회 논문집
• /
• 제27권1호
• /
• pp.31-42
• /
• 2015

소성응력분포법과 변형률적합법은 콘크리트충전 각형강관(RCFT, rectangular concrete filled tube) 기둥의 P-M조합강도 산정을 위한 대표적인 두 방법으로, 일반적으로 소성응력분포법은 근사적인 강도치를 제공하는 반면 변형률적합법은 단면에 사용되는 각 물성치의 구성방정식이 정확하다는 전제 하에서 정해에 가까운 해를 제공한다. 최근 변형률적합법에 따른 RCFT기둥의 P-M조합강도 산정에 관한 필자의 연구에 따르면, 현재 연구된 외부 강관으로 구속된 콘크리트 구성방정식이 부정확하기 때문에, 변형률적합법을 통해 산정된 다양한 물성치를 가지는 콘크리트와 강재의 조합으로 이루어진 단면의 P-M조합 강도가 부정확하게 산정되는 것으로 나타났다. 이에 따라 본 연구에서는 기존에 수행된 실험결과를 분석하여 콘크리트충전 각형 강관기둥의 P-M 조합강도 예측을 위한 변형률적합법에 활용될 수 있는 충전콘크리트의 구성방정식을 제시하고 그 타당성을 입증하였다. 본 연구에서 추구하는 모형은 실무적용을 위한 우회적이고 현상학적 모형으로, 외부 강재와 내부 콘크리트 간 상대강도비와 강재의 판폭두께비의 P-M조합강도에 대한 영향을 압괴변형률의 크기에 반영하여 단면내의 힘의 재분배 정도를 조절함으로써 실험결과와 합치하는 결과를 얻어내는 모형이다. 이를 위해 현 규준에서 제시하고 있는 압괴변형률 0.003의 일괄적 제한의 한계를 지적하였으며, 상대강도비와 판폭두께비의 P-M조합강도에 대한 영향을 압괴변형률의 크기에 반영하여 단면내의 힘의 재분배 정도를 조절함으로써 실험결과와 합치하는 결과를 얻어내는 모형을 제시하였다.

• Structural Engineering and Mechanics
• /
• 제19권6호
• /
• pp.653-677
• /
• 2005

Concrete filled steel tubular columns (CFT) are widely used in civil engineering works, especially in large scale of works because of high strength, deformation, toughness and so on. On the other hand, as a kind of strengthening measure for seriously damaged reinforced concrete piers of viaduct in Hansin-Awaji earthquake of Japan in 1995, reinforced concrete piers were wrapped with steel plate. Then, a new kind of structure appeared, that is, reinforced concrete filled steel tubular column (RCFT). In this paper, compression test and bending-shearing test on RCFT are carried out. The main parameters of experiments are (1) strength of concrete, (2) steel tube with or without rib, (3) width-thickness ratio and (4) arrangement of reinforcing bars. According to the experimental results, the effect of parameters on mechanical characteristics of RCFT is analyzed clearly. At the same time, strength evaluation formula for RCFT column is proposed and tested by experimental results and existed recommendations (AIJ 1997). The strength calculated by the proposal formula is in good agreement with test result. As a result, the proposed evaluation formula can evaluate the strength of RCFT column properly.

• Steel and Composite Structures
• /
• 제17권4호
• /
• pp.517-533
• /
• 2014

Experimental results of 39 specimens including concrete columns, RC columns, hollow steel tube columns, concrete filled steel tubular (CFT) columns, and reinforced concrete filled steel tubular (RCFT) columns are presented. Based on the experimental results, the load-carrying capacity, confined effect, ductility, and failure mode of test columns are investigated. The effects of the main factors such as width-thickness ratio (the ratio of external diameter and wall thickness for steel tubes), concrete strength, steel tube with or without rib, and arrangement of reinforcing bars on the mechanical characteristics of columns are discussed as well. The differences between CFT and RCFT are compared. As a result, it is thought that strength, rigidity and ductility of RCFT are improved; especially strength and ductility are improved after the peak of load-displacement curve.

• 한국산학기술학회논문지
• /
• 제16권5호
• /
• pp.3344-3352
• /
• 2015

본 연구는 외상성 뇌손상 환자를 대상으로 한국형 전산화 인지재활프로그램(CoTras)이 전두엽-집행기능에 미치는 효과를 알아보고자 하였다. 2013년 8월부터 2014년 3월까지 경남 창원에 위치하는 C병원에 내원한 외상성 뇌손상 환자 10명을 두 그룹으로 무작위 할당한 후 실험군에게 한국형 전산화 인지재활프로그램을, 대조군에는 자가인지훈련을 1일 1회, 주 5회, 4주 동안 적용하고 그룹 간 비교를 실시하였다. 이때 중재의 효과를 검증하기 위하여 한국판 몬트리올 인지평가(Korean Montreal Cognitive Assessment; K-MoCA), 시계 그리기 검사(Executive Clock Drawing Test; ECDT), 선로잇기 검사(Trail Making Test; TMT), Rey-도형 검사(Rey Complex Figure Test; RCFT)를 사용하였다. 그 결과, 실험군은 K-MoCA, TMT, RCFT-delayed recall에서 유의하게 향상된 반면(p<.05), 대조군은 모든 평가에서 유의한 변화가 없었다. 또한, K-MoCA, TMT, RCFT-delayed recall에서 실험군과 대조군의 변화량이 서로 유의한 차이가 있음을 확인하였다(p<.05). 본 연구는 한국형 전산화 인지재활프로그램이 외상성 뇌손상 환자의 전두엽-집행기능을 향상시키기 위해 국내 임상 환경에서 사용하기에 적절한 중재 도구임을 지지한다.

• International Journal of Concrete Structures and Materials
• /
• 제10권2호
• /
• pp.143-147
• /
• 2016

In recent years, some modifications were introduced in the stress-strain relationship of the steel in order to develop a more efficient shear model for reinforced concrete members. The last contribution in this sense corresponding to the Refined Compression Field Theory (RCFT, 2009); this theory proposed a steel constitutive model that has account the tension stiffening area prescribed by technical codes, what simplifies all the design process. However, under certain design conditions supported by such codes, the RCFT model does not provide a real (non-complex) solution for the steel yield strain when the prescribed tension stiffening area is considered; then the load-strain response cannot be computed. In this technical note, the tension stiffening area is fixed in order to guarantee the application of the embedded steel constitutive model for all the standard design range.