• Magazine of the Korea Concrete Institute
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• v.10 no.2
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• pp.137-146
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• 1998

본 연구에서는 콘크리트 속에서 인장과 전단을 받는 FRP 다우얼의 거동과 파괴를 예측할 수 잇는 수리적인 파괴 해석 모델을 개발하였다. 다우얼 파괴해석 모델은 다우얼 작용과 파괴기준에 대한 두 개의 하위 모델로 구성되어 있는데 이들을 수정, 결합하여 만들어졌다. 다우얼 작용에 대한 모델로는 BEF 모델을 기초로 하여 두가지의 지수를 새로이 정의, 사용하였는데 하나는 콘크리트지지 강성을 변화시키기 위한 변위 정도 지수이고 다른 하나는 긴장된 케이블의 반력을 고려하기 위한 인장 지수이다. 인장과 전단이 작용하는 FRP다우얼의파괴 모델로는 Tsai-Hill 파괴기준이 사용되었고 이 기준을 적용하기 위하여 파괴 계수를 정의하였다. 개발된 파괴 해석 모델은 긴장된 FRP다우얼의 극한 전단력과 극한 변위를 예측하는데 사용하였고, 해석결과는 여러 인장응력을 가진 FRP 다우얼의 시험결과와 비교하였다.

• Magazine of the Korea Concrete Institute
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• v.10 no.1
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• pp.133-141
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• 1998

FRP는 비부식성 및 고강도의 뛰어난 성질에도 불구하고 콘크리트 구조에 사용하는 데 있어서 소성의 결핍 및 낮은 전단강도와 같은 몇가지의 기술적인 단점을 가지고 있다. 특히 이 두가지 성질은 프리스트레스트 콘크리트보에 있어서 다우얼 작용이 일어나는 전단균열 단면에서와 같이 인장과 전단의 복합효과가 일어날 때 텐던의 조기 파괴를 일으키기 쉽다. 본 논문에서는 탄소 FRP연선을 사용한 프리스트레스트 콘크리트보에서의 텐던파열에 의한 전단파괴를 연구하였다. 전단시험 결과에 의하면 전단 텐던 파괴는 FRP를사용한 프리스트레스트 보에서만 일어나는 유일한 파괴형식으로 보의 전단강도를 저감시키는 것으로 확인되었다. 이러한 전단 텐던 파괴 과정을 규명하기 위하여 다우얼 시험을 실시하고 최초로 실용적인 시험장치 및 과정을 소개하였다. 다우얼 시험 결과에 의하면 FRP 연선은 인장과 전단의 상호작용에 의해 Tsai-Hill 파괴 기준에 따라 파괴되었다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.4A
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• pp.303-309
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• 2011

Laminated rubber bearing is the most commonly used device for seismic base isolation of bridge structures. It is important to know performance and behavior characteristics of the laminated rubber bearings. The main evaluation factors of the rubber bearing are classified as compressive, shear and tensile behavior characteristics. The reference data of compressive and shear characteristics are rich, but the reference data of tensile characteristics is scarce. In this study, tensile test results of the rubber bearing with variation of shape factor and shear deformation are investigated for mechanical property. When tensile deformation in normal condition is increasing, tensile cycle behavior curve becomes non-linear and tensile breaking point is 300%. On the other hand, tensile breaking point is shear deformation condition is about 40%. Furthermore, when shape factor is lower, tensile breaking point is decrease. This results mean that tensile breaking point is decreased in triaxial tensile deformation because of cracks caused by internal void of the rubber bearings. This experimental data can be used as the reference data of tensile characteristics for designing seismic isolation of structures.

• Journal of the Korean Wood Science and Technology
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• v.39 no.4
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• pp.351-358
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• 2011

This study has been carried out to understand the fracture characteristics of the tension wood of Quercus mongolica under the shear and bending stress. Macroscopically, the wood fluff in the shear surface appeared more frequently in tension wood than sound wood, and more coarse wood fluffs were observed in 30% than 10% moistured shear surface. In the fractured tension wood from bending stress, more thick and long wood fiber appeared than sound wood. The observation using scanning electron microscope indicated that both sound and tension wood samples from radial shear surface showed the intrawall dominated failure and the fracture surface of the ray parenchyma cell showed the transwall dominated failure. In tangential shear surface, wood fiber surface showed the intrawall failure and short and coarse wood fiber was observed in tension wood. Ray parenchyma cell of sound and tension wood samples showed the transwall failure. The surfaces of tension wood’s ray parenchyma cell were relatively clean. The fractured tension wood from bending stress showed unsharp and flat wood fiber compared with sound wood.

• Journal of the Korean Ceramic Society
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• v.28 no.1
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• pp.19-19
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• 1991

Fracture of Al2O3 tubes for different loading path under combined tension/torsion was investigated. Macroscopic directions of crack propagation agreed well with the maximum principal stress criterion, independent of the loading path. However, fracture strength from the proportional loading test(τ/σ= constant) showed either strengthening or weakening compared to that from uniaxial tension, depending on the ratio τ/σ. The Weibull theory was capable to predict the strengthening of fracture strength in pure torsion, but not the weakening in the proportional loading condition. The strengthening or weakening of fracture strength in the proportional loading condition was explained by the effect of shear stresses in the plane of randomly oriented microdefects. Finally, a new empirical fracture criterion was proposed. This criterion is based on a mixed mode fracture criterion and experimental data for fracture of Al2O3 tubes under combined tension/torsion. The proposed fracture criterion agreed well with experimental data for both macroscopic directions of crack propagation and fracture strengths.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.11
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• pp.5566-5571
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• 2012

Block shear failure is one of limit states, and demands great caution in designing the tension member or connection joint of steel structures. From many studies and design specification, it is shown that the effect of the bolted connection type on the block shear failure was not considered. In order to investigate the effect of the bolted connection type(bearing type connection and slip critical connection) on the mode/strength of the block shear failure, tensile experiment is conducted in this study. Differences about the failure mode according to the design specification, bearing type connection, and slip critical connection are proposed from the analysis of test results. The variation of the block shear failure strength due to the frictional force in the slip critical connection is also investigated.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.12 no.3
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• pp.293-308
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• 1999

이 논문에서는 패널, 깊은 보 그리고 전단벽과 같이 평면응력상태하에 있는 철근콘크리트 구조물의 비선형 유한요소해석에 있어서의 직교이방성 콘크리트 구성 모델의 적용성을 보여준다. 등가의 일축 변형을 개념을 토대로 콘크리트의 구성 관계가 주변형률 축과 일치하고 하중이력에 따라 회전하는 직교하는 축에 대해 제시된다. 제안된 모델은 이축 압축응력상태와 인장-압축 응력상태에서 각각 압축강도의 증가와 인장 저항력의 감소효과를 보여주는 이축 파괴영역의 정의를 포함한다. 인장균열이 발생한 후, 콘크리트의 압축강도의 감소효과가 제시되고, 인장강화효과로 알려진 철근에 의해 지지되는 콘크리트의 인장응력이 고려된다. 평균응력과 평균변형률 개념을 사용하여 힘의 평형, 적합조건 그리고 철근과 철근을 둘러싼 콘크리트 사이의 부착응력-슬림 관계를 토대로 인장강화효과를 모사하기 위한 모델이 제안된다. 유한요소 모델에 의한 예측은 유용한 실험자료와의 비교에 의해 입증된다. 이 논문에서는 해석결과와 이상화한 전단 패널실험으로부터 얻어진 실험값의 비교연구가 수행되고, 제안된 모델의 타당성을 보여주기 위해 서로 다른 응력상태하의 전단 패널 보와 벽체의 힘-변위 관계를 평가하였다.

• Journal of the Korea Concrete Institute
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• v.19 no.5
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• pp.655-664
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• 2007

The inherent characteristic of concrete tensile cracks, directional nonlocal crack damage, causes so-called rotating tensile crack damage and softening of compressive strength. In the present study, a plasticity model was developed to describe the behavior of reinforced concrete planar members In tension-compression. To describe the effect of directional nonlocal crack damage, the concept of microplane model was combined with the plasticity model. Unlike existing models, in the proposed model, softening of compressive strength as well as the tensile crack damage were defined by the directional nonlocal crack damage. Once a tensile cracking occurs, the microplanes of concrete are affected by the nonlocal crack damage. In the microplanes, microscopic tension and compression failure surfaces are calculated. By integrating the microscopic failure surfaces, the macroscopic failure surface is calculated. The proposed model was implemented to finite element analysis, and it was verified by comparisons with the results of existing shear panel tests.

• Journal of the Korea Concrete Institute
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• v.29 no.1
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• pp.53-64
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• 2017

Ultra-high performance fiber-reinforced concrete (UHPFRC) is characterized by a post-cracking residual tensile strength with a large tensile strain as well as a high compressive strength. To determine a material tensile strength of UHPFRC, three-point loading test on notched prism and direct tensile test on doubly notched plate were compared and then the design tensile strength is decided. Shear tests on nine I-shaped beams with varied types of fiber volume ratio, shear span ratio and size effect were conducted to investigate shear behavior in web. From the test results, the stress redistribution ability represented as diagonal cracked zone was quantified by inclination of principal stress in web. The test results shows that the specimens were capable of resistance to shear loading without stirrup in a range of large deformation and the strength increase with post-cracking behavior is stable. However at the ultimate state all test specimens failed as a crack localization in the damaged zone and the shear strength of specimens is affected by shear span ratio and effective depth. Strength predictions show that the existing recommendations should be modified considering shear span ratio and effective depth as design parameters.

• Magazine of the Korea Concrete Institute
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• v.9 no.5
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• pp.225-231
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• 1997

콘크리트 압축강도 및 전단스팬비의 변화에 의한 고강도 철근콘크리트 춤이 큰 보의 전단거동 및 내력특성을 파악하기 위한 실험적 연구를 하였다. 춤이 큰 보는 하중작용점과 하중지지점을 연결하는 사균열의 확대에 의해 취성전단파괴양상을 나타내었으며 하중작용점 하중 지지점의 콘크리트 압괴를동반하는 전단압축 및 전단인장파괴 형태로 최종파괴되었다. 전단스팬비가 감소함에 따라 사균열전단응력 및 최대전단응력은 크게 증가하였으며, ACI 및 CIRIA규준식은 부재의 최대전단응력을 비교적 정확하게 예측하고 있음을 파악하였다.