• 한국강구조학회 논문집
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• 제12권6호
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• pp.769-777
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• 2000

본 논문은 CFT기둥-H형강보 철골 모멘트 접합부의 보-패널존 강도비에 의한 내진거동을 평가하였다. 보에 대한 패널존의 상대강도를 주요변수로 하였다. 각 실험체는 $H-350{\times}175{\times}7{\times}11$ 보(SS400)와 ${\boxe}-250{\times}250{\times}9$, ${\boxe}-250{\times}250{\times}12$ 기둥(SPSR400)으로 제작되었다. 실험체의 에너지 흡수량은 5.2~12.7(tm)의 분포를 나타냈다. 패널존이 보에 비해 너무 강하거나 약하면, 에너지 흡수능력이 열등했다. 철골 모멘트 저항골조에 있어서 본 실험의 결과는 패널존의 항복을 허용하는 것이 내진거동에 유리함을 나타내고 있다.

• 콘크리트학회지
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• 제11권1호
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• pp.149-160
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• 1999

본 논문은 고강도 콘크리트기둥에 대한 설계방법을 검증하는 연구의 일부로서, 보통강도 및 고강도 콘크리트기둥시편에 대하여 편심하중의 재하실험을 수행하여 파괴거동을 관찰하고 기둥강도를 측정하였다. 기둥시편은 모두 32개로 콘크리트 압축강도, 종방향 철근비, 세장비, 재하편심을 실험의 주요변수로 선정하였다. 콘크리트 압축강도는 356~951 kg/$cm^$ 이며, 종방향철근비는 1.13~5.51 %, 세장비는 19, 40, 61의 3 종류로 하였다. ACI의 직사각형 응력블럭, Ibrahim과 MacGregor의 수정된 직사각형 응력블럭, 사다리꼴 응력 블럭을 이용한 기둥강도해석과 축력-모멘트-곡률해석을 통한 기둥강도해석을 수행하였으며, 실험결과와 비교분석하였다. 현시방서에서 적용하고 있는 직사각형 응력블럭은 철근비가 낮은 고강도 콘크리트기둥에 대하여 비안전측의 축력-모멘트강도를 제공한다. 축력-모멘트-곡률해석을 통한 기둥강도해석시에는 콘크리트 응력-변형률곡선의 최대응력을 결정하는 $k_3$ 값에 따라 정확성 및 안전성이 좌우된다. 또한, 본 논문에서는 재하실험을 통한 기둥의 파괴거동, 압축연단 극한변형률, 응력블럭변수 등을 비교분석하였다.

• Computers and Concrete
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• 제12권6호
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• pp.831-850
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• 2013

The high strength materials have been more widely used in reinforced concrete structures because of the benefits of the mechanical and durable properties. Generally, it is known that the ductility decreases with an increase in the strength of the materials. In the design of a reinforced concrete beam, both the flexural strength and ductility need to be considered. Especially, when a reinforced concrete structure may be subjected an earthquake, the members need to have a sufficient ductility. So, each design code has specified to provide a consistent level of minimum flexural ductility in seismic design of concrete structures. Therefore, it is necessary to assess accurately the ductility of the beam sections with high strength materials in order to ensure the ductility requirement in design. In this study, the effects of concrete strength, yield strength of reinforcement steel and amount of reinforcement including compression reinforcement on the complete moment-curvature behavior and the curvature ductility factor of doubly reinforcement concrete beam sections have been evaluated and a newly prediction formula for curvature ductility factor of doubly RC beam sections has been developed considering the stress of compression reinforcement at ultimate state. Based on the numerical analysis results, the proposed predictions for the curvature ductility factor are verified by comparisons with other prediction formulas. The proposed formula offers fairly accurate and consistent predictions for curvature ductility factor of doubly reinforced concrete beam sections.

• 콘크리트학회논문집
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• 제11권4호
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• pp.147-156
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• 1999

Current design code states that the strength reduction factor shall be permitted to be increased linearly from that for axial compression to that for flexure as the design axial load strength $\Phi$cPn decrease from 0.1fckAg to zero. Since this empirically adopted axial load level of $\Phi$cPn=0.1fckAg considers only sectional area and concrete strength, the other variables such as steel ratio, steel yielding strength, and steel arrangement can not be considered. This research is performed to investigate the consistency and the rationality of the code requirement for determination of column design strength. A nonlinear axial force-moment-curvature analysis was conducted in order to investigate the ductility of reinforced concrete column sections. As the result of ductility analysis, it was found that the ductility at the axial force of $\Phi$cPn=0.1fckAg represented a lock of consistency for the various variable contained sections. Therefore, a more reasonable application method of strength reduction factor is proposed, that is based on the strain ductility index.

• International Journal of Concrete Structures and Materials
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• 제18권1E호
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• pp.11-16
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• 2006

The use of the current ACI 318 stress block parameters has been reported to provide unconservative estimations of the moment capacities for high-strength concrete columns. Accordingly, several concrete stress block parameters have been recently proposed. This paper discusses various concrete stress block parameters for high-strength concrete and their influences on the code provisions. In order to adopt the proposed stress block parameters to the design code, it is necessary to understand the impact of the change of the stress block parameters on various aspects of the code provisions. For this purpose, the influence of using of different stress block parameters on the location of the neutral axis and the tensile strain in extreme tension steel as well as the axial and moment capacities are investigated. In addition, the influence on the prestressed concrete members is also elucididated.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2002년도 가을 학술발표회 논문집
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• pp.593-598
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• 2002

Routinely, strength method for the determination of the nominal moment of reinforced concrete beam is assumed to also be suitable for strengthening beams with carbon fiber sheets since typically strengthening beams compromise 98% by volume of reinforced concrete. Flexural capacity of strengthening beam is absolutely dependent upon the type of reinforcement materials, amount of reinforcement, anchoring system, adhesion capacity between reinforcement material and concrete. Therefore, it might be incorrect to use strength method for analysis and design of strengthening beam without considering the differences in the load-deflection curves, mechanism of failure, state of stress distribution, failure strain of the reinforcement. An flexural analysis based on force equilibrium and strain comparability has been developed for strengthening beam. Systematic experimental investigations are compared with analytical results. Then, the adaptation of strength method for strengthening beam have also been discussed.

• 한국해양공학회지
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• 제6권2호
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• pp.103-112
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• 1992

The calculation method which takes into account the shear lag effects on the ultimate transverse bending moment of a SWATH(Small Waterplane Area Twin Hull) ship has been developed. In case of the ultimate bending strength analysis of conventional monohull ships and general box girder structures, the hypothesis that plane section remains plane after bending can be employed but not in the case of the structures having wide flange. For the ultimate bending strength analysis of such structures, a new method which can take into account the effect of shear lag on the ultimate bending strength has been developed by adopting more reasonable assumption that warping distortion of the section takes place inthe same way as the actual stress distribution. Finally, the proposed method has been applied to a a SWATH cross deck structure.

• 콘크리트학회논문집
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• 제12권5호
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• pp.101-110
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• 2000

A practical approach of calculating the ultimate strength of composite beams with unreinforced web opning is proposed through shear behavioral tests. In this method, the slab shear contribution at the opening is calculated as the smaller value of the pullout capacity of shear connector at the high moment end and the one way shear capacity of slab. A simple interaction equation is used to predict the ultimate strength under simultaneous bending moment and shear force. Strength prediction by the proposed method is compared with previous test results and the predictions by other analytical methods. The comparison shows that the proposed method predicts the ultimate capacity with resonable accuracy.

• Structural Engineering and Mechanics
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• 제8권6호
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• pp.531-546
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• 1999

The paper presents an experimental and theoretical study on the influence of steel fibers and longitudinal tension and compression reinforcements on immediate and long-term deflections of high-strength concrete beams of 85 MPa (12,300 psi) compressive, strength. Test results of eighteen beams subjected to sustained load for 180 days show that the deflection behavior depends on the longitudinal tension and compression reinforcement ratios and fiber content; excessive amount of compression reinforcement and fibers may have an unfavorable effect on the long-term deflections. The beams having the ACI Code's minimum longitudinal tension reinforcement showed much higher time-dependent deflection to immediate deflection ratio, when compared with that of the beams having about 50 percent of the balanced tension reinforcement. The results of theoretical analysis of tested beams and those of a parametric study show that the influence of steel fibers in increasing the moment of inertia of cracked transformed sections is most pronounced in beams having small amount of longitudinal tension reinforcement.

• Steel and Composite Structures
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• 제6권5호
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• pp.387-400
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• 2006

This paper discusses the composite mechanism and its effect upon the behavior of a steel reinforced concrete (SRC) member subjected to a flexural load. The relationship between member strength and deformation is established using the bond strength between the steel and reinforced concrete. An analytical model is proposed and used to incorporate the sectional strains and bond strength at the elastic and inelastic stages for moment-curvature relationship derivation. The results from the flexural load tests are used to validate the accuracy of the proposed model. Comparisons between the experimental information and the analytical results demonstrate close moment-curvature relevance, which justifies the applicability of the proposed method.