• Magazine of the Korea Concrete Institute
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• v.5 no.1
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• pp.103-113
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• 1993

일반적으로 스터럽이 없는 철근콘크리트 보의 전단강도는 콘크리트 압축강도, 주철근비, 전단스팬비 및 보 유효깊이에 좌우된다는 것이 많은 연구를 통하여 밝혀지고 있다. 따라서, 본 연구에서는 고강도 콘크리트를 사용한 철근콘크리트 보의 거동 및 전단강도 특성을 분석하기 위하여 주철근비, 전단스팬비 및 보 유효깊이를 변수로 두고 총 22개의 단철근 보 실험체를 제작하여 실험을 수행하였다. 실험결과는 ACI규준식, Zsutty식 및 Bazant & Kim식의 예측값들과 함께 비교, 분석되었는데, ACI 규준식은 주철근비 및 전단스팬비의 효과를 과소평가할 뿐만 아니라 유효깊이가 915mm인 큰 보의 경우 안전측이 아니어서 이에 대한 고려가 필요할 것으로 판단된다. Zsutty식은 주철근비의 효과를 적절하게 평가하는 것으로 나타났으며, Bazant & Kim 식은 유효깊이 증가에 따른 전단강도 감소 경향을 잘 예측하는 것으로 나타났다. 또한, 다른 연구자들의 실험치와 비교, 분석해본 결과 주철근비 및 전단스팬비의 효과는 콘크리트 압축강도 수준에 따라 큰 변화가 없는 것으로 판단된다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.2
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• pp.403-413
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• 2014

For the reliable design of the structural concrete by the strut-tie model approaches of current design codes, the effective strengths of concrete struts must be determined with sufficient accuracy. Many values and equations for the effective strengths have been suggested until now. As those are for the two-dimensional concrete struts, however, it is inappropriate to employ them in the strut-tie model designs of three-dimensional structural concretes. In this study, an approach, that determines the effective strengths of three-dimensional concrete struts consistently and accurately by reflecting the state of 3-dimensional stresses, the 3-dimensional failure criteria of concrete, the degree of cracks (or tensile strains of reinforcing bars crossing the struts), the strut's longitudinal length, the deviation angle between strut orientation and compressive principal stress flow, compressive strength of concrete, and the degree of concrete confinement by reinforcing bars, is proposed. To examine the validity of the proposed approach, the ultimate strength analyses of 115 reinforced concrete pile caps tested to failure by previous investigators were conducted by the ACI 318-11's strut-tie model approach with the existing and proposed effective strengths of concrete struts.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05a
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• pp.383-386
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• 2005

철근콘크리트 부재가 하중을 받을 때, 응력교란구역에서의 힘의 흐름은 스트럿-타이 모델을 이용하여 효과적으로 표현할 수 있다. 그러나 스트럿-타이 모델을 이용하여 철근콘크리트 부재의 해석과 설계를 하기 위해서는 큰크리트 압축스트럿이 가지는 유효강도를 정확히 산정하여야 한다. 본 연구는 철근콘크리트 부재에 휨과 전단력이 동시에 작용할 때 발생하는 대각선 균열이 콘크리트 압축스트럿에 미치는 영향에 대해 설명하고 있다. 대각선 균열의 발생 메커니즘과 이로 인한 콘크리트 압축스트럿의 강도 저하를 이론적으로 설명하였으며, 그 결과를 철근콘크리트 보의 강도 산정에 적용하였다. 최종적으로 철근콘크리트 보의 강도 예측값을 기존 연구자들의 실험결과와 비교하여 제안된 이론의 합리성을 검증하였다.

• Journal of the Korea Concrete Institute
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• v.19 no.2
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• pp.145-151
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• 2007

The shear failure modes of FRP strengthened concrete beams are quite different to those of the beams strengthened with steel stirrups. When the beams are externally wrapped with FRP composites, many beams fail in shear due to concrete crushing before the FRP reaches its rupture strain. In order to predict the shear strength of such beams, the effective strain of the FRP must be blown. This paper presents the results of an experimental study on the performance of reinforced concrete beams externally wrapped with FRP composites and infernally reinforced with steel stirrups. The main parameters of the tests were FRP reinforcement ratio, the type of fiber material (carbon or glass) and configuration (continues sheets or strips). The experimentally observed effective strain of the FRP was compared with the strain calculated using a proposed method.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.6
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• pp.2195-2209
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• 2013

The effective strength of concrete struts must be determined accurately for the reliable strut-tie model analysis and design of structural concrete. In this study, the equations of the effective strength, which are useful for the three types of determinate and indeterminate strut-tie models of reinforced concrete deep beams employed in current design codes, are proposed. The effects of shear span-to-effective depth ratio, compressive strength of concrete, and flexural and shear reinforcement ratios are reflected in the development of the proposed equations. To examine the appropriateness of the proposed equations, the strengths of 241 reinforced concrete deep beams, all tested to shear failure, are evaluated by using the three types of strut-tie models with the existing and proposed equations.

• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.5
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• pp.105-112
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• 2013

In this study, the applicability of impact-echo method for assessment of residual strength of fire-damaged concrete is investigated. A series of standard fire test is performed to obtain fire-damaged concrete specimens. Impact-echo tests are executed on the specimens and the responses are analyzed. Compressive strengths of the fire-damaged concrete are evaluated and correlated with the ultrasonic wave velocities determined from the impact-echo responses. The effectiveness of impact-echo based ultrasonic wave velocity measurement for assessment of residual strength of fire-damaged concrete is discussed.

• Korean Journal of Construction Engineering and Management
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• v.19 no.4
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• pp.43-51
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• 2018

As the inventory of aged apartments is expected to increase explosively, the importance of maintenance to improve the durability of concrete facilities is increasing. Concrete compressive strength is a representative index of durability of concrete facilities, and is an important item in the precision safety diagnosis for facility maintenance. However, existing methods for measuring the concrete compressive strength and determining the maintenance of concrete facilities have limitations such as facility safety problem, high cost problem, and low reliability problem. In this study, we proposed a model that can predict the concrete compressive strength through images by using deep convolution neural network technique. Learning, validation and testing were conducted by applying the concrete compressive strength dataset constructed through the concrete specimen which is produced in the laboratory environment. As a result, it was found that the concrete compressive strength could be learned by using the images, and the validity of the proposed model was confirmed.

• Magazine of the Korea Concrete Institute
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• v.8 no.6
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• pp.173-182
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• 1996

An experimental research was carried out to investigate the effect of thc compressive strength of concrete on the stirrup effectiveness in shear behavior of concrete beams. For this purpose. total 24 beams of section dimension of $300{\times}600mm$ were tested: 4 specimens without web reinforcement and 20 specimens with web reinforcement in the form of vertical stirrups. Main variables were two levels(norma1 and high strength) of the compressive strength of concrete and six types of t h e shear rcinfor.cement ratios. Prior to experiment, for given sections and assumed material constants, the reference shear reinforcement ratio(${\rho}_vACI$) which leads to the flexure failure using the provisions of the ACI Building Code(AC1 318-95) was calculated. and the shear reinforcement ratios were relatively selected from the value of ${\rho}_vACI$. From test results, it was shown that thc safety factor of ACI eyuation for p1,ediction of shear strength was decreased with increasing the compressive strength of concrete in beams without stirrups. However. it was observed that as the amount of' stirrup is increased, the safety factor for high strength conci,ete beams with high stirrup ratio is ensured more than that for normal strength concrete beams. Therefore i t appears that the stirrup effectiveness of high strength concrete beams is greater than that of normal strength concrete beams.

• Magazine of the Korea Concrete Institute
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• v.10 no.2
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• pp.155-165
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• 1998

굳지 않은 콘크리트의 슬럼프손실을 저감시키기 위한 목적으로 고로슬래그 미분말 및 플라이애쉬의 혼합비율과 혼화제의 첨가방법을 변화시킨 콘크리트의 믹싱후 경과시간에 따른 슬럼프 변화에 대하여 고찰하였다. 연구결과 보통포틀랜드시멘트에 고로슬래그 비분말 또는 플라이애쉬를 혼합한 콘크리트가 혼화재를 혼합하지 않은 콘크리트보다 슬럼프손실을 줄일 수 있었으며, 고로슬래그 미분말과 플라이애쉬를 각각 50 및 5%를 혼합한 3성분계 콘크리트의 경우 슬럼프손실을 저감시키는데 유효하였다. 또한 혼화제의 일부를 15분후 분할하여 후첨가하는 혼합방법이 굳지않은 콘크리트의 슬럼프손실을 저감시키는데 가장 큰 효과가 있다. 한편 혼화재를 혼합한 3성분계 보통강도용 및 고강도용 콘크리트의 재령 28일까지의 압축강도는 혼화재를 혼합하지 않은 콘크리트보다 작았으나 재령 91일 압축강도는 31% 및 15%정도 크게 증가하였다.

• Journal of the Korea Concrete Institute
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• v.18 no.5 s.95
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• pp.639-648
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• 2006

A shear experiment of one-way monotonic loading was carried out with the shear span ratio as the main experimental variable for reinforced concrete beam. Using the finite element analysis as the experimental analysis tool and the analysis method to compute the shear resistance of small shear span ratio, a new macro-model composed of crooked main strut and sub strut is proposed in consideration of the effect of bond action between re-bar and concrete based on the experimental result. The experimental finding affirmed the validity of the proposed macro-model when the shear span ratio was at or below 0.75 and confirmed that the experimental result was the most consistent with the computed analysis result when the effective factor of concrete compressive strength was set at 0.75.