• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 봄 학술발표회 논문집
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• pp.315-320
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• 2003

Two different strength types of plain concrete plate specimens (200$\times$200$\times$60mm) were tested under different biaxial load combinations. The specimens were subjected to biaxial combinations covering the three regions of compression-compression, compression-tension, and tension-tension. The loading platens with Teflon pads were used to reduce a confining effect in boundary surface between the concrete specimen and the solid platen. The principal deformations in the specimens were recorded, and the failure modes along with each stress ratio were examined. Based on the strength data, the failure envelops were developed for each type of plain concrete. The biaxial stress-strain responses of concrete plate specimens for three biaxial loading regions were also plotted. The test data indicated that the strength of concrete under biaxial compression ($f_2 / f_1$$_1$=-1/-1) is about 17 percent larger than under uniaxial compression.

• 대한토목학회논문집
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• 제28권2A호
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• pp.165-170
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• 2008

각국의 강구조물 시공현장에서 사용되고 있는 고장력볼트의 인장강도는 일반적으로 1,000 MPa급이 주종을 이루고 있으나, 고강도강과 극후판의 개발과 교량 지간의 장대화로 인하여 강도가 큰 새로운 볼트 개발이 요구되고 있다. 한편, 반복적인 하중이 작용하는 곳에서 인장연결부에 사용되는 고장력볼트에 인장피로파괴 사례가 발생되고 있으나 아직까지 우리나라에서는 이에 대한 이론 및 실험적인 연구가 없는 실정이다. 따라서, 본 연구에서는 현재 일반적으로 사용하고 있는 F8T, F10T볼트와 새로이 개발된 F13T, F13T-N볼트에 대해서 인장피로실험을 수행하였다. 고장력볼트에 대한 피로강도평가는 반복횟수 200만회에 95% 하한신뢰도분석을 하여 수행하였고, 이를 기초로 3가지의 피로강도 기준안을 제시하였다. 또한, KS나사형상의 볼트와 새로이 제안된 나사선 형상의 볼트에 대한 피로강도에 대해서 비교 검토하였다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 춘계 학술발표회 제16권1호
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• pp.438-441
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• 2004

This paper presents the results of the experimental study on the performances of reinforced concrete beams rehabilitated by external unbonded high tension steel-bar. Design variables for the experiment in this study includes the position of anchorage zone of the high tension steel bar, the anchorage length of the reinforcing steel bar and the types of the shear strengthening measures. 5 specimens were tested with one point monotonically increased loads and structural performances such as strength capacities, ductility capacities and failure modes were analysed. It is found that the structural performance of the rehabilitated beams are strongly depended on the location of anchorage zone of the high tension steel-bars. In the case that anchorage zone is located near the critical shear zone, it is observed that the rehabilitated beam is failed in brittle failure mode and the additional shear strengthening is necessitated. But if anchorage zone is properly located or additional shear strengthening device is provided properly, it is also observed that the strength capacity of the rehabilitated beams could be increased more than $200\%$ by the proposed method.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 춘계 학술발표회 제20권1호
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• pp.861-864
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• 2008

This study was performanced to investigate the fractural and fatigue behavior of ultra-strength steel fiber reinforcement concrete. The tension softening diagram can describe the post-cracking behavior of concrete in tension. In this paper, Three points bending tests with a notch have been carried out to investigate tensile properties of the steel fiber reinforced concrete(SFRC) according to variation of the height. Poly-linear approximation method combined with FEM analysis is applied to the steel fiber reinforced concrete to determine the tension softening diagrams and also to certify the validity of the method. The simulated load-CMOD curves using the determined softening diagrams though the poly-linear approximation method completely agree with the measured ones.

• 한국염색가공학회지
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• 제2권3호
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• pp.51-58
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• 1990

Cotton fabrics were mercerized in ammonia water, sodium hydroxide and mixture of ammonia/sodium hydroxide, slack and under tension. X-ray and infrared spectra analyses were used to measure crystallinity of treated cottons. Changes due to swelling, which took place in the accessible regions were determined by moisture regain and dye adsorption. In addition to that crease recovery was compared mutually, and breaking strength-elongation compared, too. Both ammonia water and caustic treatments produced changes in morphology (swollen fibers, decrease in convolutions) and in fine structure of the cellulose (increase accessibility as measured by increased moisture regain, dye adsorption). X-ray diffraction showed partial recrystallization into cellulose III lattic after tension treatment with ammonia water. Both reagents produced increased cotton elongation-at-break with slack mercerization, increased cotton breaking strength with tension mercerization, and increased moisture regain or dye adsorption with slack mercerization.

• 한국자동차공학회논문집
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• 제6권5호
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• pp.20-27
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• 1998

According as the member of the automobile body structure have been thinned their thickness and have become high strength, each part of the body structure has been put more severe stress condition. And, because fatigue strength of the spot welded lap joint is influenced by its geometrical and mechanical factors, welding condition and etc., there needs a quantitative and systematic evaluation method for them. In this study, by considering nugget edge of the spot weld part of the IB-type spot welded lap joint under tension-shear load to the ligament crack. fatigue strength of various IB-type spot welded lap joints was estimated with the stress intensity factor(S.I.F.) KIII which is fracture mechanical parameter. We could find that fatigue strength evaluation of the IB-type spot welded lap joints by KIII is more effective than the maximum principal stress ($\sigma$1max) at edge of the spot weld obtained from FEM analysis.

• 콘크리트학회지
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• 제4권4호
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• pp.171-179
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• 1992

본 연구에서는 전단-스팬비가 1.5에서 2.5 범위의 고강도 콘크리트 보에 대해 기존 규준식의 안전여부를 확인하고, 사균열강도와 극한전단강도를 결정하기 위해 총 15개의 시험체를 제작하여 실험적 연구를 수행하였다. 주요변수는 전단-스팬비(a/d=1.5, 2.0, 2,5)와 수직전단철근비(Rv=0, 25, 50, 75, 100%, Rv=[$ ho$v / $\rho$v(ACI)] 100)이며, 콘크리트 압축강도(f＇c=747kg/$ extrm{cm}^2$와 인장철근비($\rho$w=0.0377)는 일정하다. 실험결과 본 연구의 전단-스팬비의 범위에서 ACI 318-89 (11-31)식은 일반적으로 수직전단철근에 의해 저항되는 전단강도를 상당히 과소평가하는 것으로 나타났다. 따라서 수직전단철근에 대한 영향이 재고되어야 할 것이다.

• 한국강구조학회 논문집
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• 제10권1호통권34호
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• pp.101-113
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• 1998

횡방향 맞대기 용접부를 갖는 고장력볼트 시험체를 대상으로 정적 및 피로실험을 실시하여 맞대기용접부가 마찰이음부의 정적 및 피로거동에 미치는 영향을 규명하였다. 그 결과 마찰면 내부 및 외부에 맞대기 용접부가 존재하면 이음부의 피로강도는 감소하는 경향이 있으나 시방서에서 규정하는 피로한계(B등급) 이상을 만족하는 것을 알 수 있었다. 특히 피로강도는 마찰면 외부에 맞대기 용접부가 존재하는 경우가 더 낮은 경향을 나타내었다.

• 콘크리트학회논문집
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• 제15권5호
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• pp.739-746
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• 2003

Various researches on the application of polymer dispersions to the cement mortar and concrete have been carried out in many countries like America, Japan and Germany and so on due to their high performance and good modification effect. PAE of polymer dispersion widely used in situ was employed that the high flowability may be induced in the cement mortar. In order to investigate the modification of cement mortar with high flowability by PAE and fracture mode of adhesive strength properties in tension of that, experimental parameters were set as PAE solid-cement ratio(P/C) and cement: fine aggregate(C:F) and the experiments such as unit weight, flow, consistency change, crack resistance and segregation that inform on the general properties have been done. Adhesion in tension is measured with a view to comprehending the properties and fracture mode in tensile load. Consistency change of cement mortar modified by PAE did grow better as the ratio of PAE solid-cement increased and was much superior to that of resin based flooring such as polyurethane and epoxy which recorded the loss of consistency in 90 min. after mixing. Adhesive strength in tension increased with continuity during curing period and showed the maximum in case of C:F=1:1 and P/C=20%.

• 한국세라믹학회지
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• 제28권1호
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• pp.20-28
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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($\tau$/$\sigma$= constant) showed either strengthening or weakening compared to that from uniaxial tension, depending on the ratio $\tau$/$\sigma$. 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.