• Magazine of the Korea Concrete Institute
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• v.10 no.2
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• pp.119-126
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• 1998

본 연구는 철근비와 보강판비를 조정한 보강철근비를 변수로 탄소섬유쉬트 접착된 철근콘크리트 보에 대하여 그 변형특성과 강도특성 및 파괴모드를 실험적으로 고찰한 것이다. 철근비와 보강판비가 증가할수록 최대내력은 증가하는 경향을 보이지만 탄소섬유쉬트의 겹수가 증가할수록 철근비 증가의 경우와는 달리 에너지흡수능력이 저하된다. 철근비와 보강판비에 따른 파괴모드를 구분하고 시험결과와 비교, 고찰하였던 바 파괴모드와 연성의 측면에서 보강철근비 е의 한계값을 0.87 max으로 제안하였다．탄소섬유쉬트와 철근콘크리트 보의 합성작용이 철근항복이후까지 유지되어 비선형적인 거동을 보임으로써 구조적거동이 양호하게 나타나는 것으로 입증되었다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.35 no.1
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• pp.93-99
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• 2015

This paper is on a practical method for determination of the economical steel ratio in RC flexural members with an equal safety factor. The cost functions of each material and labor are considered to construct the cost function. Then, an equation for determination of the economical flexure steel ratio with the lowest construction cost were proposed. It was found that a relevant steel ratio is recommended to be 0.65~1.0% for designing singly reinforced rectangular beam.

• Journal of the Korea Concrete Institute
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• v.16 no.6 s.84
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• pp.795-803
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• 2004

To prevent the shear failure that occurs abruptly with no sufficient warning, the minimum amount of shear reinforcement should be provided to reinforced concrete(RC) beams. The minimum amount of shear reinforcement of RC beams is influenced by not only compressive strength of concrete but also shear span-to-depth ratio and ratio of tensile longitudinal reinforcement. In this paper, 14 RC beams were tested in order to observe the influences of shear span-to-depth ratio, ratio of tensile longitudinal reinforcement, and compressive strength of concrete. The test results indicated that the rate of shear strength to the diagonal cracking strength of RC beams with the same amount of shear reinforcement increased as the ratio of tensile longitudinal reinforcement increased, while it decreased as the shear span-to-depth ratio increased. The observed test results were compared with the calculated results by the current ACI 318-02 Building Code and the proposed equation.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.6
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• pp.1-9
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• 2017

Spiral reinforcement in a circular column plays an effective role in the ductile behavior of a column through position fixing and buckling restraining of the longitudinal reinforcement, and confining core-concrete. Each country has suggested the minimum volumetric ratio of spiral reinforcement in order to secure the ductility of concrete columns. The minimum volumetric ratio of spiral reinforcement suggested by ACI 318-14 and the national concrete structure design standard was developed based on the theory of Richard et al. (1928); furthermore it has been used until now. However, their theory cannot consider the effects of high strength concrete and high strength reinforcement, and arrangement condition of the spiral reinforcement. In this study, a modified minimum volumetric ratio equation is suggested, which is required to improve the ductility of reinforced concrete circular columns and to recover their stress. The modified minimum volumetric ratio equation suggested here considers the effect of the compressive strength of concrete, the yield strength of spiral reinforcement, the cross sectional area of columns, the pitch of spiral reinforcements and the diameter of spiral reinforcement. In this paper, the validity of the minimum volumetric ratios from ACI 318-14 and this study was investigated and compared based on the results of uniaxial compression experiment for specimens in which the material strength and the spiral reinforcements ratio were used as variables. In the end of the study, the modification method for the suggested equation was examined.

• Magazine of the Korea Concrete Institute
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• v.10 no.3
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• pp.117-124
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• 1998

본 연구는 고성능 철근콘크리트 보의 연성능력에 관한 실험이다. 실험변수로는인장철근비( )와 하중재하형태(1점가력과 2점가력)가 있다. 콘크리트의 실린더 압축강도가 800-900㎏/㎠, 슬럼프 20∼25㎝ 및 슬럼프 플로우가 60∼70㎝인 고성능 철근콘크리트 보의 휨 실험 결과,고성능 콘크리트는 일반강도 콘크리트보다 취성적인 성질을 나타냈으며, 이러한 성질은 고성능 콘크리트의 연성능력을 감소시켰다. 고성능철근콘크리트의 경우 등가응력블록 변수는 MacGregor블록이나 New Zealand 규준을 사용하는 것이 바람직하다. 또한, 극한 곡률을 구할때는 cu= 0.0042값을 사용하는 것이 타당하다고 사료된다. 고성능 철근콘크리트 보의 경우, 현재 ACI 규준의 철근비에서 허용하는 2 및 4 이상의 연성지수 확보는 각각 '/ 0.30 범위에서 정적하중 상태의 경우 철근비가 - '=0.60 b이하에서 가능하고 휨 부재의 모멘트 재분배를 위한 경우는 철근비를 - '=0.33 b이하로 낮추어야 할 것으로 판단된다.

• Journal of the Korea institute for structural maintenance and inspection
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• v.9 no.1
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• pp.101-111
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• 2005

In this study, it is investigated the modified modulus of elasticity of the reinforced concrete columns including the longitudinal reinforcing steels as well as the confinement effect of the core concrete due to the transverse reinforced steel through the literature reviews. Equations are derived in order to evaluate the modified modulus of elasticity for the reinforced compressive concrete including the confinement effect. The finite element analysis for the 20 story reinforced concrete building is undertaken as a case study depending on the steel ratio and modulus of elasticity, and the analysis results are discussed.

• Magazine of the Korea Concrete Institute
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• v.5 no.2
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• pp.129-139
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• 1993

본 연구에서는 철근콘크리트 기둥의 거동을 예측하기 위하여 층상화 방법을 이용한 유한요소 해석방법이 제안되었다. 콘크리트의 강도와 철근비가 기둥의 극한강도와 거동에 미치는 영향을 규명하기 위하여 세장비가 10, 60, 100인 정방형 단면(80$\times$80mm)을 갖는 30개의 기둥에 대하여 실험을 수행하였다. 이때, 콘크리트의 강도는 25.5, 63.5, 86.2MPa로, 철근비는 1.98, 3.95%로 변화시켰다. 또한, 단부조건은 양단힌지로 하고, 편심량은 기둥은 양단에서 같은 방향으로 24mm로 동일하게 하였다. 본 연구에서 제안된 해석방법은 철근콘크리트 기둥의 거동을 잘 예측하며, ACI의 모멘트 확대계수법은 고강도 콘크리트 장주에 대해서는 안전측이 아닌 것으로 나타났다. 콘크리트의 강도가 기둥의 극한강도에 미치는 영향은 기둥의 세장비가 증가할수록 감소하였으며, 콘크리트의 강도가 커질수록 세장기둥의 좌굴파괴 가능성은 증가하였다. 또한, 철근비를 증가시킬 경우, 기둥의 축력이 최대가 될 때의 모멘트가 증가되었으며, 기둥의 극한강도 증가량은 단주보다는 장주에서 더 크게 나타났다. 철근비 증가에 의해 나타나는 이러한 기둥의 극한강도 증가량과 모멘트 증가량은 콘크리트의 강도가 커질수록 증대되었다.

• Journal of the Korea Concrete Institute
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• v.29 no.2
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• pp.179-187
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• 2017

The design provisions for the maximum steel ratio in reinforced concrete flexural members is normally provided to ensure sufficient ductility and economy by steel yielding at member failure. In the Concrete Structural Design Code (2012), the maximum steel ratio is expressed in terms of a net strain in tensile steel, and leading to very high steel ratio in the case of using high strength materials. Thereby, this may result in difficulty to satisfy a required workability at concrete placing. On the contrary, in the Korean Highway Bridge Design Code (Limit State Design) the maximum steel ratio is given in terms of the maximum neutral axis depth ratio that is 0.4. From these results, a rational model for the maximum steel ratio is suggested so as to satisfy a ductility as well as a workability.

• Journal of the Korea Concrete Institute
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• v.26 no.2
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• pp.143-150
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• 2014

To avoid abrupt torsional failure due to concrete crushing before yielding of torsional reinforcement and control the diagonal crack width, design codes specify the limitations on the yield strength of torsional reinforcement of RC members. In 2012, Korean Concrete Institute design code increased the allowable maximum yield strength of torsional reinforcement from 400 MPa to 500 MPa based on the analytical and experimental research results. Although there are many studies regarding the shear behavior of RC members with high strength stirrups, limited studies of the RC members regarding the yield strength of torsional reinforcement are available. In this study, twelve RC beams having different yield strength of torsional reinforcement and compressive strength of concrete were tested. The experimental test results indicated that the torsional failure modes of RC beams were influenced by the yield strength of torsional reinforcement and the compressive strength of concrete. The test beams with normal strength torsional reinforcement showed torsional tension failure, while the test beams with high strength torsional reinforcement greater than 480 MPa showed torsional compression failure. Therefore, additional analytical and experimental works on the RC members subjected to torsion, especially the beams with high strength torsional reinforcement, are needed to find an allowable maximum yield strength of torsional reinforcement.

• Journal of the Korea Concrete Institute
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• v.25 no.6
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• pp.641-648
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• 2013

Current design codes regulate the minimum torsional reinforcement requirement for reinforced concrete members to prevent their brittle failure. The minimum torsional reinforcement ratio specified in the current national code and ACI318-11, however, have problems in the minimum longitudinal reinforcement ratio for torsion, the equilibrium condition in space truss model, and a marginal strength, etc. Thus, in order to overcome such shortcomings, this study presents a rational equation for minimum torsional reinforcement ratio that can provide a sufficient margin of safety in design. The minimum torsional reinforcement ratio proposed in this study was compared to the test results available in literature, and it was confirmed that it gave a proper margin of safety for all specimens studied in this paper.