• Title, Summary, Keyword: 낮은 수직응력

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Anisotropic Shear Strength of Artificially Fractured Rock Joints Under Low Normal Stress (낮은 수직응력 하에서 인공 절리면의 전단 이방성에 관한 연구)

  • 곽정열;이상은;임한욱
    • Tunnel and Underground Space
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    • v.13 no.3
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    • pp.169-179
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    • 2003
  • Anisotropic shear strength of rock joints is studied based on the artificially fractured specimens using experimental and analytical methods. Series of direct shear tests are performed to obtain the strength, stiffness and friction angle of joints under various low normal stresses and shearing directions. The results of shear strength and stiffness show anisotropic value according to shearing direction under low normal stress specially less than 2.45 MPa. But, the effect of joint roughness on strength decreases with increasing normal stress. To estimate more effectively the peak shear strength under low normal stress, the modified Barton's equation is suggested.

Shear Behavior Characteristics of Rock Joints Considering Roughness Parameters (암석 절리면의 거칠기와 전단거동의 특성 분석)

  • Kim, Dong-Kyu;Hong, Young-Ki;Kim, Jong-Woo
    • Tunnel and Underground Space
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    • v.26 no.5
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    • pp.384-395
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    • 2016
  • Both the roughness measurement tests and the multi-stage shear tests were carried out on the 110 rock joint samples in order to investigate the influences of rock type, joint roughness and normal stress on the shear behaviour of rock joints. Test samples were composed of quartz porphyry, dacite, granite and gneiss, which were classified into three detailed groups according to their JRC values. Roughness parameters of rock joints were analyzed by roughness measurement tests, and shear characteristics were also investigated by multi-stage shear tests. Both peak shear strength and shear stiffness were increased as both joint roughness and normal stress were increased, whereas dilation angles showed lower values at the lower roughness and higher normal stress conditions. Besides, shear characteristics obtained from all tests of four different rock types with different rock strengths showed irrelevant details, therefore the influences of both joint roughness and normal stress on shear behaviors were found to be more considerable than the strength of intact rock. The results obtained from both multi-stage shear tests and direct shear tests were finally compared, where the dilation angles obtained from multi-stage shear tests were found to be valid only for the first normal stress conditions.

Shear Behavior of Rough Granite Joints Under CNS Conditions (일정 수직강성 조건하 화강암 인장절리의 전단거동 특성)

  • Park, Byung-Ki;Lee, Chang-Soo;Jeon, Seok-Won
    • Tunnel and Underground Space
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    • v.17 no.3
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    • pp.203-215
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    • 2007
  • Stability and mechanical deformation behavior of rock masses are highly dependent on the mechanical characteristics of contained discontinuities. Therefore, mechanical characteristics of the discontinuities should be considered in the design of tunnel and underground structures. In this study, direct shear tests for rough granite joints were carried out under constant normal stiffness conditions. Effects of initial normal stress, shear velocity, and surface roughness on the characteristics of shear strength and deformation behaviors were examined. Results of shear testing under constant normal stiffness conditions reveal that shear behaviors could be classified into two categories, based on the amount of decrease in shear stress at the Int peak shear stress. With initial normal stiffness increasing, it turned out that shear displacement at peak stress and the first peak shear stress increased, however friction angle and friction coefficient showed decrease. In case of shear stiffness and average friction coefficient, it turned out that they are not dependent on the initial normal stress. Minor effects of shear velocity on rough joints were observed in several shear quantities. However, the effects of shear velocity were insignificant regardless of the normal stress increase. Change of shear strength and deformation characteristics on joint roughness were examined, however, it turned out that the variations were attributed to deviation of shear test specimens.

End-Shape Effect for Stress Concentration Reduction of Composite Single-Lap Bonded Joint (끝단형상에 따른 복합소재 단일겹치기 체결부의 응력집중 저감에 관한 연구)

  • Kim, Jung-Seok;Hwang, Jae-Yeon
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.35 no.3
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    • pp.333-340
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    • 2011
  • We evaluated the stress-reduction effect for different shapes of a composite adherend with or without a spew fillet. Six different single-lap joint specimens were modeled and assessed using nonlinear finite element analysis. Moreover, we investigated the effect of the stiffness ratio of the adherend and adhesive. The single-lap joint with normal tapering had the highest stress values, and the single-lap joint with reverse tapering and a spew fillet had the lowest stress values. The composite adherends with higher stiffness had lower stress values, and the adhesives with lower stiffness had lower stress values.

A Study on Shear Behaviors for the Rock Joint in the Constant Normal Stiffness Condition (일정수직강성(CNS) 조건에서 절리면 전단거동에 관한 연구)

  • Kim Yong-Jun;Lee Young-Huy;Kim Sun-Ki;Kim Chu-Hwa
    • Tunnel and Underground Space
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    • v.15 no.5
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    • pp.330-337
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    • 2005
  • Apart from the geometric features of the rock joints, the shear characteristics of rock mass subject to shear force are also significantly affected by the boundary conditions in the neighborhood of the rock mass. The boundary conditions of the rock mass can be classified into 4 categories according to the stress state of the rock joint, of which the constant normal load (CNL) is the most used for shear test and produces the lowest shear strength and different behavior. In this study, the shear behavior under constant normal stiffness condition was able to replicated by the graphic method normalized by the test results under constant normal stress condition.

A Stress Analysis of Double-deck Train with Composite Material (복합재료 2층 기차의 응력해석)

  • 이영신;김재훈;박병준;김기남;주정수
    • Proceedings of the KSR Conference
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    • pp.75-82
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    • 1999
  • 본 연구의 목적은 구체 경량화의 일환으로써, 복합재료(3-X Board, Al extrusion panel, etc) 사용에 대한 가능성을 판단하기 위한 기초자료를 구축하는데 있다. 해석 대상은 2층 기차의 객차부분이고, 구체에 적용하는 복합재료는 3-X Board를 이용하였다. 구체의 구조 건전성을 평가하기 위해 상용 유한요소 프로그램을 이용하여 다양한 하중 하에서의 응력해석을 수행하였다. 구체에 사용되는 복합재료(3-X board)의 응력발생 경향을 파악하는 것이 목적이므로, 상세한 모델보다는 단순화한 모델을 이용하였다. 응력집중은 센터실(center sill), 1층 바닥과 측면과의 연결부, 그리고, 구체의 앞부분 창문 모서리에서 발생하였다. 압축 및 수직하중 하에서의 응력값들은 재료의 항복강도 내에 존재하였으나, 고유진동수는 제한 값보다 낮은 값을 갖았다. 현재 상세 모델에 대한 해석을 수행 중에 있다. 본 연구는 복합재료(3-X board)가 적용된 구체에 대한 초기 연구로써 만족할 만한 결과를 제시한다.

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Elastic Wave Characteristics in Cemented Engineered Soils (고결된 Engineered Soils의 탄성파 특성)

  • Lee, Chang-Ho;Yoon, Hyung-Koo;Lee, Woo-Jin;Lee, Jong-Sub
    • Journal of the Korean Geotechnical Society
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    • v.24 no.2
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    • pp.87-97
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    • 2008
  • Behaviors of cemented engineered soils, composed of rigid sand particle and soft rubber particle, are investigated under $K_o$ condition. The uncemented and cemented specimens are prepared with various sand volume fractions to estimate the effect of the cementation in mixtures. The vertical deformation and elastic wave velocities with vertical stress are measured. The bender elements and PZT sensors are used to measure elastic wave velocities. After cementation, the slope of vertical strain shows bilinear and is similar to that of uncemented specimen after decementation. Normalized vertical strains can be divided into capillary force, cementation, and decementation region. The first deflection of the shear wave in near field matches the first arrival of the primary wave. The elastic wave velocities dramatically increase due to cementation hardening under the fixed vertical stress, and are almost identical with additional stress. After decementation, the elastic wave velocities increase with increase in the vertical stress. The effect of cementation hinders the typical rubber-like, sand-like, and transition behaviors observed in uncemented specimens. Different mechanism can be expected in decementation of the rigid-soft particle mixtures due to the sand fraction. a shape change of individual particles in low sand fraction specimens; a fabric change between particles in high sand fraction specimens. This study suggests that behaviors of cemented engineered soils, composed of rigid-soft particles, are distinguished due to the cementation and decementation from those of uncemented specimens.

Effects of Coronal Thread Pitch in Scalloped Implant with 2 Different Connections on Loading Stress using 3 Dimensional Finite Element Analysis (연결부 형태가 다른 두 가지 scallop 임플란트에서 경부 나사선 피치가 응력 분포에 미치는 영향 : 삼차원적유한요소분석)

  • Choi, Kyung-Soo;Park, Seong-Hun;Lee, Jae-Hoon;Huh, Jung-Bo;Yun, Mi-Jung;Jeon, Young-Chan;Jeong, Chang-Mo
    • Journal of Dental Rehabilitation and Applied Science
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    • v.29 no.2
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    • pp.111-118
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    • 2013
  • Purpose of present study is to investigate the effects of thread pitch in coronal portion in scalloped implant with 2 different connections on loading stress using 3 dimensional finite element analysis. Scalloped implant with 4 different thread pitches (0.4mm, 0.5mm, 0.6, and 0.7mm) in the coronal part was modeled with 2 different implant-abutment connections. Platform matching connection had the same implant and abutment diameter so that they were in flush contact at the periphery while platform mismatching connection had smaller abutment diameter than implant so that their connection was made away from periphery of implant-bone interface. Occlusal loading of 100N force was applied vertically and 30 degree obliquely to all 8 models and the maximum von Mises bone stress was identified. Loading stress as highly concentrated in cortical bone. Platform mismatching scalloped implant with small thread pitch (0.4mm) model had consistently lowest maximum von Mises bone stress in vertical and oblique loads. Platform matching model had lowest maximum von Mises bone stress with 0.6mm thread pitch in vertical load and with 0.4mm thread pitch in oblique load. Platform mismatching connection had important roles in reducing maximum von Mises bone stress. Scalloped implant with smaller coronal thread pitch showed trend of reducing maximum von Mises bone stress under load.

Shear Strength of Reinforced High Strength Concrete Deep Beams with Geometric Condition (기하학적 경계조건을 고려한 고강도 철근 콘크리트 춤이 큰 보의 전단강도)

  • 오정근;신성우
    • Magazine of the Korea Concrete Institute
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    • v.10 no.1
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    • pp.109-118
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    • 1998
  • 전단거동에 의해 지배되는 고강도 철근콘크리트 춤이 큰 보의 전단역학적 거동 및 전단강도특성을 고려한 이론식을 제시하고자 소성이론에 근거한 극한해석에서 상계치정리를 이용하여 이론적 전개를 하였으며, 고강도 R/C춤이 큰 보의 전단응력에 영향을 미치는 콘크리트 압축강도, 수직전단보강근 및 수평잔단보강근의 보강효과를 고려한 이론식을 제시하였으며, 수평철근 즉 주인장철근 및 수평전단보강근의 장부작용을 고려하였다. 실험결과와 비교할 때 제안식은 수직잔단보강근의 전단보강효과를 과대평가하고있으며, 수평전단보강근의 효과를 적절하게 평가하고 있음을 나타내었다. 또 전단스팬비가 0.5, 0.85인 경우에는 제안식에 의한 값이 다소 낮게 나타내, 전단스팬비가 낮은 경우는 다소 과소평가하는 것으로 나타났다.

Ring Shear Characteristics of Waste Rock Materials in Terms of Water Leakage (누수유무에 따른 광산폐석의 링전단특성)

  • Jeong, Sueng Won
    • The Journal of Engineering Geology
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    • v.26 no.3
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    • pp.307-314
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    • 2016
  • Shear characteristics of soils can be investigated using various types of shear stress measuring apparatus. Ring shear tests are often applied for examining the residual shear strength under the unlimited deformation. This paper presents drainage-consolidation-shear velocity dependent undrained shear strengths measured in terms of water leakage. A series of ring shear tests were performed under the constant normal stress (50 kPa) and controled shear velocity ranging from 0.01~1 mm/sec under the undrained condition. As a result, undrained shear strengths are dependent on shear velocity. It exhibits that straining hardening behavior is observed for the shear velocity lower than 0.1 mm/sec; however, the strain softening behavior is observed for the shear velocity higher than 0.1 mm/sec. Water leakage can cause the increase in shear stress irrespective of shear velocity. Shear stress increases with increasing amount of water leakage. It is due to the fact that the small grains and water flow out through the rubble edge in the ring shear box. Repetitive saturation and consolidation processes may minimize the error.