• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1999년도 학회창립 10주년 기념 1999년도 가을 학술발표회 논문집
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• pp.385-388
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• 1999

This study is to investigate experimentally the shear capacity of high-strength reinforced concrete beams subjected to monotonic loading. Nine reinforced concrete beams using high strength concrete $(f'c=380kg/\textrm{cm}^2)$ are tested to determine their diagonal cracking and ultimate shear capacity. The main variables are shear span-depth ratio a/d=1.5, 2.5, 3.5, and shear reinforcement ratio. All specimens are 170mm wide and have a total depth of 300mm. The test results indicate that ACI 318-95(b) Code for shear capacity gave closest agrement with the exsprimental results. The beams with a shear spear-depth ratio 1.5 and 2.5. ACI 318-95 Code underestimates shear strength carried by vertical shear reinforcements.

• International Journal of Concrete Structures and Materials
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• 제10권sup3호
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• pp.53-63
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• 2016

Steel fiber-reinforced prestressed concrete (SFRPSC) members typically have high shear strength and deformation capability, compared to conventional prestressed concrete (PSC) members, due to the resistance provided by steel fibers at the crack surface after the onset of diagonal cracking. In this study, shear tests were conducted on the SFRPSC members with the test variables of concrete compressive strength, fiber volume fraction, and prestressing force level. Their localized behavior around the critical shear cracks was measured by a non-contact image-based displacement measurement system, and thus their shear deformation was thoroughly investigated. The tested SFRPSC members showed higher shear strengths as the concrete compressive strength or the level of prestress increased, and their stiffnesses did not change significantly, even after diagonal cracking due to the resistance of steel fibers. As the level of prestress increased, the shear deformation was contributed by the crack opening displacement more than the slip displacement. In addition, the local displacements around the shear crack progressed toward directions that differ from those expected by the principal strain angles that can be typically obtained from the average strains of the concrete element. Thus, this localized deformation characteristics around the shear cracks should be considered when measuring the local deformation of concrete elements near discrete cracks or when calculating the local stresses.

• The Korean Journal of Ceramics
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• 제3권2호
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• pp.73-81
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• 1997

In this paper, it is intended to present more reproducible and quantitative method for adhesion assemssement. In scratch test, micromechanical analysis on the stress state beneath the indenter was carried out considering the additional blister field. The interface adhesion was quantified as work of adhesion through Griffith energy approach on the basis of the analyzed stress state. The work of adhesion for DLC film/WC-Co substrate calculated through the proposed analysis shows the identical value regardless of distinctly different critical loads measured with the change of film thickness and scratching speed. On the other hand, uniaxial loading was imposed on DCL film/Al substrate, developing the transverse film cracks perpendicular to loading direction. Since this film cracking behavior depends on the relative magnitude of adhesion strength to film fracture strength, the quantification of adhesion strength was given a trial through the micromechanical analysis of adhesion-dependence of film cracking patterns. The interface shear strength can be quantified from the measurement of strain $\varepsilon$s and crack spacing $\lambda$ at the cessation of film cracking.

• 한국농공학회지
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• 제44권3호
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• pp.73-84
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• 2002

Nominal shear strength of concrete beam is the combined strength of concrete shear strength and steel shear strength in current design code. But Torsional moment strength of concrete is neglected in calculation of the nominal torsional moment strength of reinforced concrete beam in current revised code. Tensile stress of concrete strut between cracks is still in effect due to tension stiffening effect. But the tensile stresses of concrete after cracking are neglected in bending and torsion in design. The torsional behavior is similar to the shear behavior in mechanics. Therefore the torsional moment strength of concrete should be concluded to the nominal torsional moment strength of reinforced concrete beam. To verify the validity of the proposed model, the nominal torsional moment strengths according to CEB, two ACI codes(89, 99) and proposed model are compared to experimental torsional strengths of 55 test specimens found in literature. The nominal torsional moment strengths by the proposed model show the best results.

• 대한토목학회논문집
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• 제29권5D호
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• pp.619-625
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• 2009

본 연구에서는 반사균열 및 러팅을 저감시키는 것으로 알려진 섬유보강 아스팔트 포장의 성능을 극대화하기 위한 방안을 찾기 위하여 3곳의 구간에서 현장 시험시공을 실시하였다. 섬유보강 아스팔트의 부착 전단강도에 영향을 미칠 수 있는 시공 도중 발생 가능한 문제점을 정의하고 시험시공 시 이에 맞는 시공조건을 의도적으로 만들어 주었다. 시험시공 직후와 약 1년이 지난 후 시공 상태가 양호한 위치와 불량한 위치에서 각각 코어를 채취하고 부착 전단강도 실험을 수행하여 그 결과를 비교 분석하였다. 이를 통하여 섬유보강 아스팔트의 성능을 향상시키기 위하여 현장에서 지켜야 할 만한 규정을 제안하였다.

• 한국산학기술학회논문지
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• 제15권9호
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• pp.5844-5853
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• 2014

본 논문에서는 고인성 섬유 시멘트 복합재료(DFRCC)를 이용한 철근콘크리트(RC) 보의 전단파괴거동에 대한 실험적 연구결과를 제시하였다. 이를 위해 $150{\times}300{\times}1,000mm$ 크기의 보를 총 10개 제작하여 변위제어에 의한 4점휨파괴실험을 실시하였다. 주요 실험변수로는 DFRCC에 의한 보강의 유무, 보강시 그라인딩을 통한 사전 표면처리 그리고 사전 균열발생 유무를 설정하였다. 실험으로부터 재하시작 후 파괴시까지 보의 하중-처짐곡선, 전단균열 및 휨균열 발생하중 그리고 파괴시 전단강도를 측정하였다. 실험결과, DFRCC에 의한 보강시 적절한 두께와 사전 표면처리를 적절히 시행할 경우 기존 RC보의 전단강도를 약 99% 이상 효과적으로 복원할 수 있는 것으로 나타났으며, 보다 신뢰성있는 연구를 위하여 실제 노후화된 구조물에서 채취한 부재에 대한 추가적인 실험과 이론적 연구가 필요한 것으로 판단된다.

• 한국구조물진단유지관리공학회 논문집
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• 제26권3호
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• pp.48-54
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• 2022

본 연구는 균열에 의한 콘크리트 전단벽 강성저하 영향 평가를 위해 수행되었으며, 극한 내지진 하중의 60%까지 재하한 비선형 해석 결과, 사전 균열효과에 의해 비손상 대비 진동수의 12%정도 진동수가 감소하였으며 강성 측면에서 23%정도의 감소현상을 나타냈다. 단계적으로 지진하중의 크기를 증가시킨 비선형 해석 결과, 지진하중의 세기가 커짐에 따라 콘크리트 전단벽체에 전단균열이 발생하여 진전함을 파악하고, 반복이력에 의한 에너지 손실과 강성 저하가 뚜렷하게 발생함을 알 수 있었다. 또한 두 가지 콘크리트 강도와 전단벽 제원에 대하여 지진하중의 크기가 극한 내지진 하중에 근접함에 따라 진동수의 감소량은 비손상 대비 10~40%정도로 나타났으며, 강성의 경우 비손상 대비 40%정도 수준까지 감소할 수 있는 것으로 나타났다.

• 한국도로학회논문집
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• 제19권3호
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• pp.31-43
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• 2017

PURPOSES : The objective of this study is to verify the effect of fiber grid reinforcement on the long-term performance of asphalt pavement overlaid on old concrete pavement by performing field investigation, laboratory test, and finite element analysis. METHODS : The reflection cracking, roughness, and rutting of fiber grid reinforced overlay sections and ordinary overlay sections were compared. Cores were obtained from both the fiber grid reinforced and ordinary sections to measure bonding shear strength between the asphalt intermediate and asphalt overlay layers. Fracture energy, displacement after yield, shear stiffnesses of the cores were also obtained by analyzing the test results. Finite element analysis was performed using the test results to validate the effect of the fiber grid reinforcement on long-term performance of asphalt pavement overlaid on the old concrete pavement. The fatigue cracking and reflection-cracking were predicted for three cases: 1) fiber grid was not used; 2) glass fiber grid was used; 3) carbon fiber grid was used. RESULTS : The reflection-cracking ratio of fiber grid reinforced sections was much smaller than that of ordinary sections. The fiber grid reinforcement also showed reduction effect on rutting while that on roughness was not clear. The reflection-cracking was not affected by traffic volume but by slab deformation and joint movement caused by temperature variation. The bonding shear strength of the fiber grid reinforced sections was larger than that of the ordinary sections. The fracture energy, displacement after yield, and shear stiffnesses of the cores of the fiber grid reinforced sections were also larger than those of the ordinary sections. Finite element analysis results showed that fatigue cracking of glass or carbon fiber grid reinforced pavement was much smaller than that of ordinary pavement. Carbon fiber grid reinforcement showed larger effect in elongating the fatigue life of the ordinary overlay pavement compared to glass fiber grid reinforcement. The binder type of the overlay layer also affected the fatigue life. The fiber grid reinforcement resisted reflection-cracking and the carbon fiber grid showed the greater effect. CONCLUSIONS :The results of field investigation, laboratory test, and finite element analysis showed that the fiber grid reinforcement had a better effect on improving long-term performance of asphalt pavement overlaid on the old concrete pavement.

• Earthquakes and Structures
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• 제9권6호
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• pp.1233-1250
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• 2015

The behavior of reinforced concrete (RC) columns made from high strength materials was investigated experimentally. Six high-strength concrete specimen columns (1:4 scale), which included three with high-strength transverse reinforcing bars and three with normal-strength transverse reinforcement, were tested under double curvature bending load. The effects of yielding strength and ratio of transverse reinforcement on the cracking patterns, hysteretic response, shear strength, ductility, strength reduction, energy dissipation and strain of reinforcement were studied. The test results indicated that all specimens failed in splitting failure, and specimens with high-strength transverse reinforcement exhibited better seismic performance than those with normal-strength transverse reinforcement. It also demonstrated that the strength of high-strength lateral reinforcing bars was fully utilized at the ultimate displacements. Shear strength formula of short concrete columns, which experienced a splitting failure, was proposed based on the Chinese concrete code. To enhance the applicability of the model, it was corroborated with 47 short concrete columns selected from the literature available. The results indicated that, the proposed method can give better predictions of shear strength for short columns that experienced a splitting failure than other shear strength models of ACI 318 and Chinese concrete codes.

• 콘크리트학회지
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• 제3권3호
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• pp.141-148
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• 1991

본 논문은 전단보강이 없는 강섬유보강 고강도 철근콘크리트보의 전단거동에 관한 연구로서 전단스팬비(a/b), 섬유첨가율(Vf)의 변화에 사인장균열 전단응력 및 극한전단응력의 변화를 관찰하였다. 실험결과 섬유첨가율이 증가할수록, 전단스팬비가 감소할수록 사인장균열 전단응력 및 극한전단응력이 증가함을 보여주고 있으며, 특히 섬유첨가율이 증가함에 따라 섬유의 균열억제거동에 의해 극한전단응력이 높게 증가함을 볼 수 있다. 본 연구에 의한 실험결과를 바탕으로 각 변수에 따른 사인장균열 전단응력 및 극한전단응력에 대한 실험식을 제안하였다.