• 대한토목학회논문집
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• 제35권1호
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• pp.9-17
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• 2015

강-콘크리트 슬립실험으로 결정된 계면 계수값을 휨하중을 받는 콘크리트 충전강관 실험의 결과예측에 적용하여 콘크리트 충전강관의 계면거동과 구속효과를 평가하였다. 이를 위해 ${\phi}100mm$ 및 ${\phi}200mm$의 두 종류 강관 직경을 갖는 콘크리트 충전 강관(CFT)을 제작하여 휨 거동실험을 수행하였으며, 계면거동을 고려하는 유한요소 해석을 수행하여 거동을 예측하였다. 실험 및 해석결과의 분석을 통해 충전 콘크리트에 대한 강관의 구속효과는 강도의 계산에서 고려할 만한 정도의 영향성은 없는 것을 확인하였다. 또한, 강관과 충전콘크리트 간의 계면슬립변위는 하중 재하점 부근에서 가장 크게 발생하고 단부에 가까울수록 감소하며 전단지간 내의 계면에 작용하는 부착력이 단부에서 콘크리트의 압출을 억제함을 유한요소해석 결과를 통해 확인하였다.

• 한국구조물진단유지관리공학회 논문집
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• 제18권5호
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• pp.9-18
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• 2014

본 논문은 강-콘크리트 슬립실험으로 결정된 계면 계수값을 휨 하중을 받는 콘크리트 충전강관 합성보 실험의 결과예측에 적용하여 콘크리트 충전강관 합성보의 계면거동과 구속효과를 규명하였다. 원형단면의 콘크리트가 전단면압축을 받도록 하기 위해서 콘크리트 충전강관에 웨브와 플랜지를 추가한 콘크리트 충전강관 합성보를 사용하여 휨 거동실험을 수행하였다. 콘크리트가 전단면 압축을 받는 단부가 개방된 콘크리트 충전합성강관의 경우에는 구속효과에 의해 약 16%의 강도증진효과를 확인하였으며, 단부를 폐쇄하여 구속효과가 커진 콘크리트충전 합성강관의 경우에는 35% 정도의 큰 강도증진효과가 발생하는 것을 확인하였다. 실험과 수치해석을 통해 얻은 이러한 결과는 콘크리트 충전강관을 이용한 교량의 상부 거더나 아치리브에 대한 단면 결정에 적용되는 적용성을 갖는다.

• 한국지진공학회논문집
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• 제12권1호
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• pp.21-28
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• 2008

CFT(Concrete Filled Steel Tube)기둥은 부재의 합성효과와 경제적인 측면 때문에 최근 고층건물 시공 시 널리 쓰이고 있다. 그러나 기존의 연구문헌을 살펴보면 CFT 기둥은 강관의 항복이후 강관의 일정지점에 국부좌굴이 생기는 단점을 지니고 있다. 이러한 문제점을 해결하기 위하여 예상 국부좌굴부위를 탄소섬유쉬트로 보강하여 국부좌굴을 방지하거나 지연시키는 TR-CFT (Transversely Reinforced Concrete Filled Steel Tube) 기둥에 관한 연구가 진행되고 있다. 본 연구에서는 고강도 콘크리트를 사용한 TR-CFT기둥의 실험을 수행하였으며 휨내력에 대한 해석을 수행한 결과 실험값과 해석값이 잘 일치하였다. 또한 기존의 ACI 318 설계법은 강관내부에서 발생하는 콘크리트에 대한 구속효과를 고려하지 않아 저평가가 되어있음을 알 수 있었다.

• Advances in concrete construction
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• 제9권2호
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• pp.161-171
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• 2020

In this paper, an experimental study was conducted on the compressive behavior of steel tube confined concrete (STCC) and concrete-filled steel tube (CFST) columns with active and passive confinement. To create active confinement in the STCC and CFST specimens, an innovative method was used in this study, in which by applying pressure on the fresh concrete, the steel tube was laterally pretensioned and the concrete core was compressed simultaneously. Of the benefits of this technique are improving the composite column behavior, without the use of additives and without the need for vibration, and achieving high prestressing levels. To achieve lower and higher prestressing levels, short and long term pressures were applied to the specimens, respectively. Nineteen STCC and CFST specimens in three groups of passive, short-term active, and long-term active confinement were subjected to axial compression, and their mechanical properties including the compressive strength, modulus of elasticity and axial strain were evaluated. The results showed that the proposed method of prestressing the STCC columns led to a significant increase in the compressive strength (about 60%), initial modulus of elasticity (about 130%) as well as a significant reduction in the axial strain (about 45%). In the CFST columns, the prestressing led to a considerable increase in the compressive strength, a small effect on the initial and secant modulus of elasticity and an increase in the axial strain (about 55%). Moreover, increased prestressing levels negligibly affected the compressive strength of STCCs and CFSTs but slightly increased the elastic modulus of STCCs and significantly decreased that of CFSTs.

• Steel and Composite Structures
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• 제13권3호
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• pp.259-275
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• 2012

Concrete filled steel tubular (CFST) member has been widely used in the construction of high-rise buildings for its high axial bearing capacity. It can also be applied on long-span structures such as spatial structures or bridges not only for its high bearing capacity but also for its construction convenience. Concrete casting effect of CFST member is considered in the study of its bearing capacity in this paper. Firstly, in order to authenticate the applicability of constitutive relationship and yield criterion of steel and concrete based on FEM, two ANSYS models are built to simulate and compared with other's test. Secondly, in order to find the huge difference in bearing capacity due to different construction processes, two full-size CFST models are studied when they are horizontally cast and axially compressed. Finally, the effects of slenderness ratio (L/D) and confining parameter (D/t) of CFST members are studied to reveal the intrinsic links between bearing capacity and slenderness ratio or confining parameter.

• Steel and Composite Structures
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• 제16권1호
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• pp.59-75
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• 2014

A new concrete confinement model is developed to predict the axial load versus displacement behavior of circular columns under concentric axial load. The new confinement model is proposed for concrete filled steel tube columns as well as circular reinforced concrete columns with steel tube jacketing. Existing confinement models were evaluated and improved using available experimental data from different sets of columns tested under similar loading conditions. The proposed model is based on commonly used confinement models with an emphasis on modifying the effective confining pressure coefficient utilizing the strength of the unconfined concrete and the steel tube, the length of the column, and the thickness of the steel tube. The proposed model predicts the ultimate axial strength and the corresponding strain with an acceptable degree of accuracy while also highlighting the importance of the manner in which the steel tube is used.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 가을 학술발표회 논문집
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• pp.173-176
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• 2003

Progressive failure analysis of steel composite double T-beam is performed to investigate the mechanical effects of steel composite fabricated in the webs of double-T beam to replace concrete placing forms. The analysis is based on nonlinear finite element scheme considering material nonlinearities of concrete, reinforcing bar and PS steel. Four-parameter strength envelope defines the hardening and softening phenomena of concrete with consideration of the various levels of confining pressures. Rankine maximum strength criterion defines the elasto-plasticity of PS steel and reinforcing bar, and Von Mises $J_2$ failure criterion for steel plate which wraps the concrete webs of double T-beam. A 6m long two-span steel composite double T-beam is analyzed and compared with the experimental results.

• Earthquakes and Structures
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• 제1권3호
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• pp.269-287
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• 2010

High-strength concrete (HSC) is becoming more popular in the construction of beams and columns of tall buildings because of its higher stiffness and strength-to-weight ratio. However, as HSC is more brittle than normal-strength concrete (NSC), it may adversely affect the flexural ductility and deformability of concrete members. Extended from a series of theoretical study conducted on flexural ductility of concrete beams, the authors would in this paper investigate the effects of some critical factors including the degree of reinforcement, confining pressure, concrete and steel yield strength on the flexural deformability of NSC and HSC beams. The deformability, expressed herein in terms of normalised rotation capacity defined as the product of ultimate curvature and effective depth, is investigated by a parametric study using nonlinear moment-curvature analysis. From the results, it is evident that the deformability of concrete beams increases as the degree of reinforcement decreases and/or confining pressure increases. However, the effects of concrete and steel yield strength are more complicated and dependent on other factors. Quantitative analysis of all these effects on deformability of beams has been carried out and formulas for direct deformability evaluation are developed. Lastly, the proposed formulas are compared with available test results to verify its applicability.

• 한국강구조학회 논문집
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• 제23권4호
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• pp.439-454
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• 2011

내부구속 중공 콘크리트 충전 강관(ICH CFT: Internally Confined Hollow Concrete Filled Tube) 기둥의 비선형 해석모델을 제안하고 기존 연구자의 실험 결과를 이용하여 검증하였다. 제안된 모델은 콘크리트의 구속효과와 재료비선형성을 고려하였다. 검증결과, 제안된 해석 모델은 ICH CFT 기둥의 거동을 예측하는데 합리적이고 신뢰할 수 있는 결과를 보여주었다. 제안된 모델을 이용하여 매개변수 연구를 수행하였으며, 기둥의 거동에 영향을 미치는 주요인자로서 콘크리트의 강도, 중공비, 내부강관의 두께를 매개변수로 선택하였다. 해석결과, 콘크리트 강도와 내부강관의 두께는 기둥의 축강도와 모멘트 저항능력에 큰 영향을 주었으나, 중공비의 변화는 축강도에만 영향을 미치는 결과를 보여주었다.

• Earthquakes and Structures
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• 제15권2호
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• pp.165-178
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• 2018

The aim of this study is to investigate the efficiency of using threaded rods and steel profiles to produce a steel confining system for rehabilitation of damaged concrete corbels for the first time in literature. Some of the specimens were repaired by crack repair epoxy before being confined for further enhancement. A total of 19 two sided damaged corbels were used in the study with different mechanical properties and parameters but similar dimensions. The differences were in rehabilitation style, shear span, fiber percentage, reinforcement steel diameter, and concrete strength. The rehabilitated specimens were loaded with vertical load until failure. Four different configurations were used in the investigation. Test results show that the proposed rehabilitation technique is effective to enhance the load capacity of the corbels and to improve their ductility. Moreover, new formulations were proposed to calculate the load capacity of the rehabilitated corbels. A good fit was observed between numerical and experimental results.