• Steel and Composite Structures
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• v.12 no.6
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• pp.523-540
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• 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
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• v.11 no.5
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• pp.391-402
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• 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
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• v.16 no.6
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• pp.639-655
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• 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
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• 2008.02b
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• pp.507-512
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• 2008

This study investigated the navigation ability of patients with MCI in Virtual Environments(VE) and on the visual functioning. The participants consisted of elderly adults with/without MCI. Neuropsychological tests(RCFT, BVRT, TMT, and Digit Span), the Groton Maze Learning Test(12trials), and the VE navigation learning task(6 trials) were performed. As a result, there were significant group differences for the RCFT and BVRT, but not for the GMLT. For the VE task, there was a significant difference between the MCI and normal group and no interactions between the groups and trials were found. The VE task was correlated with The RCFT, the BVRT, and the GMLT and omnibus the RCFT and the BVRT accounted for 45% of VE performances. Thus, we concluded that patients with MCI are inferior to VE navigation and visual retention/memory play a role in navigation abilities.

• Structural Engineering and Mechanics
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• v.56 no.5
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• pp.727-743
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• 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.

• Journal of Korean Society of Steel Construction
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• v.27 no.1
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• pp.31-42
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• 2015

The plastic stress distribution method and the strain compatibility method are the two representative methods to calculate the P-M interaction strength of RCFT (rectangular concrete filled tube) columns. The plastic stress distribution method is approximate while the stress compatibility method should approach the exact solution if accurate constitutive relations of the materials involved are used. Recent study by the authors pointed out that, because of lack of accurate constitutive model for the concrete confined by the rectangular steel tube, no strain compatibility method according to the current structural provisions provides a satisfactory prediction of the P-M interaction strength of RCFT columns under various material combinations. An empirical constitutive model which can capture the stress-strain characteristics of the confined concrete of RCFT columns is proposed based on analyzing extensive exisitng test database. The key idea was to define the concrete crushing strain as a function of steel-to-concrete strength ratio and width-to-thickness ratio of steel tube. It was shown that the proposed model leads to more accurate and more consistent prediction of the P-M interaction strength of RCFT columns under general design conditions.

• Structural Engineering and Mechanics
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• v.19 no.6
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• pp.653-677
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• 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
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• v.17 no.4
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• pp.517-533
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• 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.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.5
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• pp.3344-3352
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• 2015

The purpose of this study is to investigate the effects of Korean computer-based cognitive rehabilitation program (CoTras) on frontal-executive functions in patients with traumatic brain injury (TBI). This study was performed at C hospital in Changwon, Gyeongsangnam-do, Korea from August 2013 to March 2014. Ten patients with TBI were randomly divided into two groups. The experimental group had been given CoTras once a day, five times a week for four weeks, whereas the control group had performed self-cognitive training under the same conditions. To verify the effect of intervention, the following executive function measures were used: Korean Montreal Cognitive Assessment (K-MoCA), Executive Clock Drawing Test (ECDT), Trail Making Test (TMT), Rey-Complex Figure Test (RCFT). Intervention group showed significant increase in K-MoCA, TMT, RCFT-delayed recall (p<.05). However, control group showed no significant change in any test. There was significant difference of changed scores (post test-pre test) between two groups in K-MoCA, TMT and RCFT-delayed recall (p<.05). This study showed that CoTras is effective to improve frontal-executive functions in patients with traumatic brain injury.

• International Journal of Concrete Structures and Materials
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• v.10 no.2
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• pp.143-147
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• 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.