• 한국구조물진단유지관리공학회 논문집
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• 제23권5호
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• pp.111-117
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• 2019

확대머리 SD600 고강도 인장철근으로 단부 정착된 SFRC 깊은보의 전단성능을 평가하기 위해 전단 실험을 수행하였다. 실험 변수는 주인장 철근의 단부 정착방법(확대머리 철근, 일자형 철근), 단부 정착길이, 전단보강근 유무 등이다. 전단경간비는 1을 가지는 실험체에 대한 전단실험결과, 모든 실험체는 초기 휨 균열이 발생한 후 경사균열이 진행되면서 최종적으로 압축전단파괴되었다. 확대머리 철근으로 기계적 정착된 실험체들이 일자형 철근 정착에 비하여 5.6~22.4% 더 큰 전단강도를 나타내었다. 확대머리 철근으로 기계적 정착된 실험체들에 대하여 최대하중의 75%까지는 지압응력이 전체 정착응력의 0.9~17.2%에 도달하였으나, 최대하중 시점에서 지압응력이 전체 정착응력의 22.4%~46%에 도달하여 큰 응력 부담률을 나타내었다. 이를 통하여 확대머리 지압응력에 의한 정착응력 증가가 전단강도에 큰 영향을 미침을 알 수 있다. 실험 전단강도가 실용식에 의한 전단강도의 2.68~4.65 배로 평가되어, 실용식이 전단내력을 안전측으로 평가하였다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 추계 학술발표회 제17권2호
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• pp.5-8
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• 2005

The purpose of this study is to investigate the mechanical characteristics of plain and steel fiber high strength concrete under uniaxial and biaxial loading condition. A number of plain and steel fiber high strength concrete cubes having 28 days compressive strength of 82.7Mpa (12,000psi) were made and tested. Four principal compression stress ratios, and four fiber concentrations were selected as major test variables. From test results, it is shown that confinement stress in minor stress direction has pronounced effect on the strength and deformational behavior. Both of the stiffness and ultimate strength of the plain and fiber high strength concrete increased. The maximum increase of ultimate strength occurred at biaxial stress ratio of 0.5 in the plain high strength concrete and the value were recorded 30 percent over than the strength under uniaxial condition. The failure modes of plain high strength concrete under uniaxial compression were shown as splitting type of failure but steel fiber concrete specimens under biaxial condition showed shear type failure.

• 한국재료학회지
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• 제25권11호
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• pp.630-635
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• 2015

The fatigue strength of a nickel-base superalloy was studied. Stress-controlled fatigue tests were carried out at $700^{\circ}C$ and 5 Hz using triangular wave forms. In this study, two kinds of testing procedures were adopted. One is the conventional tension-zero fatigue test(R = 0). The other was a procedure in which the maximum stress was held at 1000 MPa and the minimum stress was diverse from zero to 1000 MPa at 24 and $700^{\circ}C$. The results of the fatigue tests at $700^{\circ}C$ indicate that the fracture mechanism changed according to both the mean stress and the stress range. At a higher stress range, ${\gamma}^{\prime}$ precipitates are sheared by a/2<110> dislocation pairs coupled by APB. Therefore, in a large stress range, the deformation occurred by shearing of ${\gamma}^{\prime}$ by a/2<110> dislocations, which brought about crystallographic shear fracture. As the stress range was decreased, the fracture mode gradually changed from crystallographic shear fracture to gradual growth of fatigue cracks. At an intermediate stress range, as it became more difficult for a/2<110> dislocation pairs to shear ${\gamma}^{\prime}$ particles, cracks started to propagate in the matrix, avoiding the harder ${\gamma}^{\prime}$ particles. High mean stress induced creep deformation, that is, ${\gamma}^{\prime}$ particles were sheared by {111}<112> slip systems, which led to the formation of stacking faults in the precipitates. Thus, the change in fracture mechanism brought about the inversion of the S-N curves.

• 한국공간구조학회논문집
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• 제7권2호
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• pp.83-90
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• 2007

건축물의 고층화, 대형화에 따라 기둥이 부담해야할 하중이 증대되고, 이로 인한 기둥단면적의 증대에 효율적으로 대처하기 위해 CFT(콘크리트 충전강관)기둥의 형식을 개발하게 되었다. CFT기둥은 이질재료로 구성된 복합구조형식으로, 역학적 거동을 규명하기 위해 많은 연구가 이루어지고 있다. 본 연구는 원형과 각형의 CFT기둥에 있어서 콘크리트 코어와 강관, 두 이질재료간의 접촉면 부착응력에 대한 해석적 연구로서 비선형 해석프로그램인 ABAQUS/Standard Version 5.8을 이용하여 shear-connector의 부착형태 및 위치에 따른 부착응력을 비교하고, 접촉면의 역학적 특성에 대한 개선된 해석기법을 제시하고자 한다.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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• pp.121-126
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• 2002

The railroad cars or the commercial vehicles are generally manufactured by the spot welding. Among various kinds of spot welded lap joints, multi-lap joints are one of popular joints in manufacturing their body structures. But, fatigue strength of these joints are lower than that of base metal due to high stress concentration at the nugget edge of the spot weld and are known to considerably be influenced by welding conditions as well as the mechanical and geometrical factors. Thus, it is necessary to establish a reasonable and systematic fatigue design criterion for spot welded multi-lap joints. In this paper, the $\Delta$P-N$_{f}$ curves has been rearranged in the $\Delta$$\sigma$-N$_{f}$ relation with the maximum stress at the nugget edge of spot welded multi-lap joints subjected to tensile shear load. Consequently, the fatigue data were evaluated in terms of fracture mechanics by plotting on the $\Delta$OP-N$_{f}$ curves. From the results obtained, both of them have been revealed to be applicable to fatigue design of spot welded multi-lap joints. However, the fracture mechanical approach is found to be more effective than the maximum stress approach in the range on N$_{f}$$\geq$2x10$^{5}$ . .

• 한국지반공학회논문집
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• 제23권3호
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• pp.41-50
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• 2007

본 논문에서는 실트 함유율이 높은 모래에 대한 정규압밀 등방배수 및 비배수 삼축압축시험(NCIU 및 NCID) 결과를 나타내었다. 유효구속응력 $100\sim400kpa$하에서 실트 함유율이 63%인 낙동강 모래 시료를 사용하여 실험을 실시하였다. 실험결과, 모래질 실트는 초기에는 압축이 되지만 전체적인 응력-변형률 곡선에서 최종적으로 체적팽창반응을 보였다. 모래질 실트의 거동은 낮은 소성 특성으로 인하여 점토와 모래보다 비하여 그 특성을 묘사하기가 어려웠다. 특히, 시료는 파괴 후 전단과정에서 팽창현상을 보였다. 모래질 실트의 전단거동과 전단강도정수는 응력-변형률 거동과 Mohr-Coulomb 파괴규준에 의하여 결정되는데, 전단거동은 파괴 후 변형률 연화 경향과 같이 체적변화가 증가하는 것으로 관찰되었다. 본 논문에서 모래질 실트의 전단과정 동안에 발생되는 팽창거동은 모래 함유율 뿐만 아니라 저점착력을 가진 세립자의 함유율에 의해서도 달라졌다.

• Nuclear Engineering and Technology
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• 제56권6호
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• pp.2352-2366
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• 2024

Reinforced concrete (RC) shear walls with precast steel-concrete composite modular (PSCCM) are strongly recommended in the structural design of nuclear power plants due to the need for a large number of process pipeline crossings and industrial construction. However, the effect of the PSCCM on the mechanical behavior of the whole RC shear wall is still unknown and has received little attention. In this study, three 1:3 scaled specimens, one traditional shear wall specimen (TW) and two shear wall specimens with the PSCCM (PW1, PW2), were designed and investigated under cyclic loadings. The failure mode, hysteretic curve, energy dissipation, stiffness and strength degradations were then comparatively investigated to reveal the effect of the PSCCM. Furthermore, numerical models of the RC shear wall with different PSCCM distributions were analyzed. The results show that the shear wall with the PSCCM has comparable mechanical properties with the traditional shear wall, which can be further improved by adding reinforced concrete constraints on both sides of the shear wall. The accumulated energy dissipation of the PW2 is higher than that of the TW and PW1 by 98.7 % and 60.0 %. The failure of the shear wall with the PSCCM is mainly concentrated in the reinforced concrete wall below the PSCCM, while the PSCCM maintains an elastic working state as a whole. Shear walls with the PSCCM arranged in the high stress zone will have a higher load-bearing capacity and lateral stiffness, but will suffer a higher risk of failure. The PSCCM in the low stress zone is always in an elastic working state.

• 콘크리트학회논문집
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• 제22권4호
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• pp.527-534
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• 2010

이 연구에서는 고강도 전단보강근을 사용한 철근콘크리트 보의 부착성능을 향상시키기 위한 간편한 방법을 소개한다. 일반적으로 전단보강근의 항복강도와 보강근비는 철근콘크리트 보의 전단내력에 영향을 미친다. 그러나 철근 콘크리트 보의 부착성능은 보강근의 항복강도에는 큰 영향을 받지 않으므로 고강도 전단보강근을 사용한 경우 부착파괴의 위험성이 있다. 제안된 방법의 구조적 성능을 검증하기 위하여 총 4개의 철근콘크리트 보 실험체를 제작하고 실험하였다. 실험변수는 전단보강근의 항복강도와 보강근비 및 보강형태로 계획하였다. 실험 결과 제안된 방법은 철근콘크리트 보의 부착성능을 효과적으로 향상시킬 수 있음을 확인할 수 있었다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.250-255
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• 2008

This study utilized a high speed lap-shear test to evaluate the mechanical behavior of Sn-37Pb/Cu and Sn-37Pb/Electroless Nickel immersion Gold under bump metallization solder joints under high speed loading and hence the drop reliability. The samples were aged for 120 h at different temperatures ($120^{\circ}C,\;150^{\circ}C,\;170^{\circ}C$) and afterward tested at different displacement rates (0.01 mm/s to 500 mm/s) to examine the effects of aging on the drop life reliability. The combination of the stress-strain graphs captured from the shear tests and identifying a fracture mode dominant in the samples for different strain rates leads us to conclude that the drop reliability of solder joints degrades as the aging temperature increases, possibly due to the role of the IMC layer. This study successfully demonstrates that the analysis based on a high speed lap-shear test could be critically used to evaluate the drop reliability of solder joints.

• 한국농공학회지
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• 제36권3호
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• pp.90-99
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• 1994

To investigate the undrained shear strength characteristics of marine soils with high water content, high compressibility and weak bearing capacity, a series of undrained triaxial tests with pore pressure measurements on undisturbed and disturbed Banwol marine clay in normally consolidated and overconsolidated states is carried out. The results and main conclusions of this study are summarized as follows : 1 . When the consolidation pressure is increased, the maximum deviator stress of disturbed and undistubed clay in normally consolidated state is increased. Pore pressure parameters and internal friction angle of undisturbed clay are greater than those of disturbed clay. 2. The relationship between pore pressure and axial strain of undisturbed clay in normally consolidated state can be expressed as a hyperbolic function like stress-strain relation proposed by Kondner. 3. In the pore pressure-axial strain relation of disturbed clay in normally consolidated state, failure ratio R'f is greatly deviated in the range of 0.7~0.9 proposed by Christian and Desai. 4. For overconsolided clay, when overconsolidation ratio (OCR) is increased, normalized maximum deviator stress is increased and maximum pore pressure is decreased gradually. 5. Cohesion of overconsolidated clay is greater than that of nomally consolidated clay and internal friction angle slightly is decreased. 6. Pore pressure parameter at failure (Af) of overconsolidated clay is varied with OCR, Af becomes negative values with increment in OCR