• Title/Summary/Keyword: shear-friction

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Effect of Horizontal Resistance at Slab Bottom on Behavior of Concrete Slabs-on-Grade under Vertical Loads (지반위에 놓인 콘크리트 슬래브의 수직하중에 대한 슬래브 하부의 수평 저항의 영향 분석)

  • Shim, Jae-Soo;Kim, Seong-Min
    • International Journal of Highway Engineering
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    • v.7 no.4 s.26
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    • pp.141-150
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    • 2005
  • The behavior of the concrete slabs-on-grade considering the horizontal resistance at the slab bottom, which exists due to the shear resistance of the foundation and the friction between the slab and the foundation, has been investigated when the slabs-on-grade are subjected to the vertical load. Analytical formulations have been developed to include the effect of the horizontal resistance at the slab bottom, and the solutions have been obtained in the transformed field domain using the Fourier transform. Finite element formulations have also been developed using the plate bending elements and the flat shell elements. The solutions from the analytical and numerical models have been compared and showed very good agreement. The sensitivity of the horizontal resistance to the stresses of the concrete slab has been investigated with various values of the slab thickness, elastic modulus, and vertical stiffness of the foundation. The analysis results show that the horizontal resistance at the plate bottom can significantly affect the stresses of the slab.

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Slip Behavior of High-Tension Bolted Joints Subjected to Compression Force (압축력을 받는 고장력 볼트 이음부의 미끄러짐 거동)

  • Han, Jin Hee;Choi, Jong Kyoung;Heo, In Sung;Kim, Sung Bo
    • Journal of Korean Society of Steel Construction
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    • v.20 no.2
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    • pp.279-288
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    • 2008
  • In this study, the slip behavior of high-tension bolted joints subjected to compression force is investigated through 3D finite element analysis and experiments. The relation with sliding load, bolt deformation, and failure load are studied with the metal thickness affecting the bolted joint. The post-sliding behavior considering bolt stiffness is presented and compared with the results by finite element and experiments. The finite element model is constructed by solid elements in ABAQUS, in consideration of all the friction effects between metal plates and bolts. The stress-strain relations in the literature are used, and the sliding displacements and axial stresses around the bolt connection are investigated. The flexural buckling of species happened when the plate thickness is less than the bolt diameter. However, the shear failures of bolt occurred in the opposite case.

Passive Earth Pressure Transition Behind Retaining Walls (옹벽의 변위에 따른 정지토압에서 수동토압까지의 변화)

  • 김홍택
    • Geotechnical Engineering
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    • v.3 no.2
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    • pp.55-70
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    • 1987
  • An analytical solution procedure is described to estimate the developed passive lateral earth Pressures behind a vertical rigid retaintng wall rotating about its toe into a mass of cohesionless soil. Various stases of wall rotation, starting from an at-rest state to an initial Passive state to a full Passive state, are considered in the analysis. Condition of failure defined by a modified Mohr-coulomb criterion, together with equilibrium conditions, is used to obtain the necessary equations for the solution. Using methods of stress characteristics and numerical finite difference, a complete solution within and on the boundaries of the entire solution domain is made possible. The variations of the soil shear strength and the wall friction at various depths and stages of wall rotation are also taken into account in the analysis. The results predicted by the developed method of analysis are compared with those obtained from the experimental model tests on loose and dense sand. The comparisons show good agreements at various stages of retaining wall rotation Fin- ally, results of analytical parametric study are presented to demonstrate the effects of wall fric- tion on the resultant thrust and distribution of developed lateral earth pressures.

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Analysis of Factors Affecting the Slope Stability of Uncontrolled Waste Landfill (비위생 폐기물 매립지 사면의 안정성에 관한 영향인자 분석)

  • Yoo, Han-Kyu;Choi, Bong-Hyuck
    • Journal of the Korean GEO-environmental Society
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    • v.3 no.1
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    • pp.5-12
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    • 2002
  • The effects of ground water level, shear strength parameters of refuse, and geological condition of ground on the slope stability of uncontrolled waste landfill were studied. The Janbu method of slices based on the limit equilibrium method was used to calculate the minimum factor of safety with respect to slope stability of landfill. The analytical results showed that the factor of safety for a fully dried condition of landfill increased 2.4~2.8 times as great as that for a fully saturated condition of landfill. Under the condition of actual ground water level, the factor of safety linearly increased with increasing both cohesion and internal friction angle of refuse. Also, when the potential failure surface passed through the underlying layer, the factor of safety and shape of potential failure surface were found to depend on geological conditions of underlying layer.

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Application of a Mechanical Model for the Detailing of the End Anchorage Zone of Prestressed Concrete Members (프리스트레스 콘크리트 부재의 단부정착부의 배근상세를 위한 역학적 모델의 적용)

  • 강원호;방지환;김철희
    • Magazine of the Korea Concrete Institute
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    • v.8 no.4
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    • pp.201-211
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    • 1996
  • It is expected that recent development of the mechanical model will replace previous empirical methods of detailing. In this study, a mechanical model is proposed to analyze the behavior of the anchorage zone of prestressed concrete members. Main characteristics of the proposed model lies on its rational consideration of material properties, and concrete strength in biaxial stress state and that of local zone reinforced by spirals. Shear friction strength of concrete surrounding spirals are also considered. The results of' the proposed method as well as the known Strut-and-Tie method and nonlinear finite element analysis are compared with some typical experimental results. We get good agreement to the failure mode as well as the failure load from test results. And it can be shown that three dimentional failure mechanism, which cannot be expected by the method based on 2D analysis, can be explained by proposed model.

Comparison of Performance between Regular Drilled Shaft and Isolation Tube Drilled Shafts (일반 현장 타설 말뚝과 분리형 현장 타설 말뚝의 거동 비교)

  • Kim, Myung-Hak;O'Neill, Michael W.
    • Journal of the Korean Geotechnical Society
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    • v.16 no.1
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    • pp.211-220
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    • 2000
  • An experimental study that included detailed observation of four 305-mm-diameter drilled shafts, one reference shaft of standard design and three test shafts with isolation tubes to mitigate skin friction in the vadose zone of a clay soil profile, is described. The shafts were loaded only by naturally expanding and contraction soil over a period of 17 months. The soil at the test site was instrumented to track suction and elevation changes. Maximum ground surface movements exceeding 40 mm were observed. Heave movements of less than 1.5 mm were observed in the test shafts with isolation tubes, while movements of 5 mm were observed in the reference shaft. Unit side shear loads in the shafts protected by the isolation tubes were minimal compared to those measured in the reference shaft. This indicates that the isolation tubes were very effective.

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Experimental Study of Boundary Layer Transition on an Airfoil Induced by Periodically Passing Wake (II) -A Phase-Averaged Characteristic- (주기적 후류 내의 익형 위 천이경계층에 관한 실험적 연구(II) -위상평균된 유동특성-)

  • Park, Tae-Chun;Jeon, U-Pyeong;Gang, Sin-Hyeong
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.25 no.6
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    • pp.786-798
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    • 2001
  • This paper describes the phenomena of wake-induced transition of the boundary layers on a NACA0012 airfoil using measured phase-averaged data. Especially, the phase-averaged wall shear stresses are reasonably evaluated using the principle of Computational Preston Tube Method. Due to the passing wake, the turbulent patch is generated in the laminar boundary layer on the airfoil and the boundary layer becomes temporarily transitional. The patches propagate downstream with less speed than free-stream velocity and merge with each other at further down stream station, and the boundary layer becomes more transitional. The generation of turbulent patch at the leading edge of the airfoil mainly depends on velocity defects and turbulent intensity profiles of passing wakes. However, the growth and merging of turbulent patches depend on local streamwise pressure gradients as well as characteristics of turbulent patches. In this transition process, the present experimental data show very similar features to the previous numerical and experimental studies. It is confirmed that the two phase-averaged mean velocity dips appear in the outer region of transitional boundary layer for each passing cycle. Relatively high values of the phase-averaged turbulent fluctuations in the outer region indicate the possibility that breakdown occurs in the outer layer not near the wall.

Geotechnical characteristics and empirical geo-engineering relations of the South Pars Zone marls, Iran

  • Azarafza, Mohammad;Ghazifard, Akbar;Akgun, Haluk;Asghari-Kaljahi, Ebrahim
    • Geomechanics and Engineering
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    • v.19 no.5
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    • pp.393-405
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    • 2019
  • This paper evaluates the geotechnical and geo-engineering properties of the South Pars Zone (SPZ) marls in Assalouyeh, Iran. These marly beds mostly belong to the Aghajari and Mishan formations which entail the gray, cream, black, green, dark red and pink types. Marls can be observed as rock (soft rock) or soil. Marlstone outcrops show a relatively rapid change to soils in the presence of weathering. To geotechnically characterise the marls, field and laboratory experiments such as particle-size distribution, hydrometer, Atterberg limits, uniaxial compression, laboratory direct-shear, durability and carbonate content tests have been performed on soil and rock samples to investigate the physico-mechanical properties and behaviour of the SPZ marls in order to establish empirical relations between the geo-engineering features of the marls. Based on the experiments conducted on marly soils, the USCS classes of the marls is CL to CH which has a LL ranging from 32 to 57% and PL ranging from 18 to 27%. Mineralogical analyses of the samples revealed that the major clay minerals of the marls belong to the smectite or illite groups with low to moderate swelling activities. The geomechanical investigations revealed that the SPZ marls are classified as argillaceous lime, calcareous marl and marlstone (based on the carbonate content) which show variations in the geomechanical properties (i.e., with a cohesion ranging from 97 to 320 kPa and a friction angle ranging from 16 to 35 degrees). The results of the durability tests revealed that the degradation potential showed a wide variation from none to fully disintegrated. According to the results of the experiments, the studied marls have been classified as calcareous marl, marlstone and argillaceous lime due to the variations in the carbonate and clay contents. The results have shown that an increase in the carbonate content leads to a decrease in the degradation potential and an increase in the density and strength parameters such as durability and compressive strength. A comparison of the empirical relationships obtained from the regression analyses with similar studies revealed that the results obtained herein are reasonably reliable.

Measurements of Turbulent How in $5\times{5}$ PWR Rod Bundles With Spacer Grids (지지격자를 갖는 $5\times{5}$ PWR 봉다발에서의 난류유동 측정)

  • Yang, Sun-Kyu;Chung, Heung-June;Chun, Se-Young;Chung, Moon-Ki
    • Nuclear Engineering and Technology
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    • v.24 no.3
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    • pp.263-273
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    • 1992
  • The study on the velocity distribution and the pressure drop characteristic of the nuclear fuel assembly is of importance for the thermal hydraulic design and safety analysis. The purpose of this experimental study is to investigate the hydraulic mixing behind the different kinds of spacer grids in the now or rod bundles. In this study, the detailed hydraulic characteristics in subchannels of 5$\times$5 PWR(Pressurized Water Reactor) rod bundles were measured using one-component He-Ne LDV(Laser Doppler Velocimeter). Measurements of the axial velocity, turbulent intensities and pressure drops were peformed Lateral velocity, turbulent intensities and Reynolds shear stress were also measured by adjust-ing LDV alignment. Friction factors in rod bundles and loss coefficients for spacer grids were evaluated from the measured pressure drops. Hydraulic mixing performance for different kinds of spacer grids could be investigated by estimating the turbulent cross-flow mixing rates between neighboring subchannels.

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A Numerical Study on the Karman Vortex Generated by Breaking of Mountain Wave

  • Kang Sung-Dae;Kimura Fujio
    • Environmental Sciences Bulletin of The Korean Environmental Sciences Society
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    • v.1 no.2
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    • pp.105-117
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    • 1997
  • The formation mechanism of the vortex streets in the lee of the mountain is investigated by a three-dimensional numerical model. The model is based upon the hydrostatic Boussinesq equations in which the vertical turbulent momentum flux is estimated by a turbulence parameterization scheme, but the horizontal viscosity is assumed to be constant. The results show that Karman vortex streets can form even without surface friction in a constant ambient flow with uniform stratification. The vortex formation is related to breaking of the mountain wave, which depends on the Froude number (Fr). In the case of a three-dimensional bell-shaped mountain, the wave breaking occurs when Fr is less than about 0.8, while a Karman vortex forms when Fr is less than about 0.22. Vortex formation also depends on Reynolds number, which is estimated from the horizontal diffusivity. The vortex formation can be explained by the wave saturation theory given by Lindzen (1981) with some modification. Simulations in this study show that in the case of Karman vortex formation the momentum flux in the lower level is much larger than the saturated momentum flux whereas it is almost equal to the saturated momentum at the upper levels as expected from the saturation theory. As a result, large flux divergence is produced in the lower layer, the mean flow is decelerated behind the mountain, and the horizontal wind shear forms between unmodified ambient wind. The momentum exchange between the mean flow and the mountain wave is produced by the turbulence within a breaking wave. From the result, well developed vortices like Karman vortex can be formed. The results of the momentum budget calculated by the hydrostatic model are almost the same as nonhydrostatic results as long as horizontal scale of the mountain is 10 km. A well developed Karman vortex similar to the hydrostatic one was simulated in the nonhydrostatic case. Therefore, we conclude that the hydrostatic assumption is adequate to investigate the origin of the Karman vortex from the viewpoint of wave breaking.

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