• Title/Summary/Keyword: 체적변형률

Search Result 112, Processing Time 0.026 seconds

Effect of Cross-Sectional Dimension on the Shrinkage Property of Korean Red-Pine Wood (소나무재의 단면치수에 따른 수축률 특성)

  • Hwang, Kweonhwan;Park, Beyung-Su
    • Journal of the Korean Wood Science and Technology
    • /
    • v.37 no.3
    • /
    • pp.231-238
    • /
    • 2009
  • Red pine (Pinus densiflora) has been used for structural wood members of Korean traditional residence (HANOK) and historic wooden structures. For these constructions, generally, natural drying has conducted for long time; however, unless drying is conducted sufficiently, it could cause several drying defects such as check or warping. Shrinkage changes of red pine species for small clear specimens and big-size specimens according to the conditions of moisture contents, were examined. For the estimation of volumetric shrinkage at a special moisture content, it was more precise to divide the range of moisture contents into two groups, green to air-dry and air-dry to oven-dry. The volumetric shrinkage had no difference with specimen sizes in sapwood, but decreased as specimen size increased in heartwood.

Reproduction of Cyclic Triaxial Behavior of Unsaturated Soil using Element Simulation (요소 시뮬레이션에 의한 불포화토의 반복삼축거동 재현)

  • Lee, Chungwon
    • Journal of the Korean GEO-environmental Society
    • /
    • v.16 no.10
    • /
    • pp.5-14
    • /
    • 2015
  • Suction affects the unsaturated soil as the negative pore pressure, and leads to increases of the yield stress and the plastic shear stiffness of the soil skeleton due to the growth in interparticle stress. Hence, in this study, in order to account for these effects of suction under the dynamic loading condition such as the earthquake, the element simulation of the cyclic triaxial test using induced stress-strain relation based on cyclic elasto-plastic constitutive model extended for unsaturated soil considering the $1^{st}$ and the $2^{nd}$ yield functions was conducted. Through the stress path, stress-strain relation and relation between volumetric strain and axial strain, it was seen in all the cases that the simulation results demonstrated a good agreement with the experimental results. It is expected that the results of this study possibly contribute to the accuracy improvement on the prediction of unsaturated soil behavior under the dynamic loading condition.

Shearing Characteristics of Aluminium Rods Using Plane Strain - Shear Box Test and Close Range Photogrammetric Technique (평면변형률 전단시험과 근거리 사진계측기법을 통한 알루미늄 봉의 전단특성)

  • Lee, Yong-Joo;Song, Ki-Jung
    • Journal of the Korean Geotechnical Society
    • /
    • v.26 no.8
    • /
    • pp.5-14
    • /
    • 2010
  • To simulate two-dimensional plane-strain conditions in the laboratory model test, the side frictional resistance between the soil and thick glass or plastic sheet of the soil container should be reduced as much as possible. However, in fact this side friction cannot be removed completely. In this paper, the ground model simulated as a multi-sized aluminium rod mixture was introduced to get rid of the side frictional resistance and applied to the laboratory shear box test. In addition, an application of the close range photogrammetric technique to the shear box test was validated. As a result, it was found that a mean value of dilation angle from the close range photogrammetry was close to the dilation angle defined by the curve of shear strain vs. volumetric strain.

A Finite Element Simulation of Cancellous Bone Remodeling Based on Volumetric Strain (스폰지 뼈의 Remodeling 예측을 위한 체적 변형률을 이용한 유한요소 알고리즘)

  • Kim, Young;Vanderby, Ray
    • Journal of Biomedical Engineering Research
    • /
    • v.21 no.4
    • /
    • pp.373-384
    • /
    • 2000
  • The goal of this paper is to develop a computational method to predict cancellous bone density distributions based upon continuum levels of volumetric strain. Volumetric strain is defined as the summation of normal strains, excluding shear strains, within an elastic range of loadings. Volumetric strain at a particular location in a cancellous structure changes with changes of the boundary conditions (prescribed displacements, tractions, and pressure). This change in the volumetric strain is postulated to predict the adaptive change in the bone apparent density. This bone remodeling theory based on volumetric strain is then used with the finite element method to compute the apparent density distribution for cancellous bone in both lumbar spine and proximal femur using an iterative algorithm, considering the dead zone of strain stimuli. The apparent density distribution of cancellous bone predicted by this method has the same pattern as experimental data reported in the literature (Wolff 1892, Keller et al. 1989, Cody et al. 1992). The resulting bone apparent density distributions predict Young's modulus and strength distributions throughout cancellous bone in agreement with the literature (Keller et al. 1989, Carter and Hayes 1977). The method was convergent and sensitive to changes in boundary conditions. Therefore, the computational algorithm of the present study appears to be a useful approach to predict the apparent density distribution of cancellous bone (i.e. a numerical approximation for Wolff's Law)

  • PDF

Homogenization of Elastic Cracks in Hoek-Brown Rock (Hoek-Brown 암석에서 발생된 탄성균열의 균질화)

  • Lee, Youn-Kyou;Jeon, Seok-Won
    • Tunnel and Underground Space
    • /
    • v.19 no.2
    • /
    • pp.158-166
    • /
    • 2009
  • As a basic study for investigating the development of the stress-induced crack in Hoek-Brown rock, a homogenization technique of elastic cracks is proposed. The onset of crack is monitored by Hoek-Brown empirical criterion, while the orientation of the crack is determined by the critical plane approach. The concept of volume averaging in stress and strain component was invoked to homogenize the representative rock volume which consists of intact rock and cracks. The formulation results in the constitutive relations for the homogenized equivalent anisotropic material. The homogenization model was implemented in the standard FEM code COSMOSM. The numerical uniaxial tests were performed under plane strain condition to check the validity of the propose numerical model. The effect of friction between the loading plate and the rock sample on the mode of deformation and fracturing was examined by assuming two different contact conditions. The numerical simulation revealed that the homogenized model is able to capture the salient features of deformation and fracturing which are observed commonly in the uniaxial compression test.

Experimental Study on the Triaxial Compressive Behaviour of Unsaturated Compacted Silt under Various Suction Levels (다양한 석션 레벨에서의 불포화실트의 삼축압축거동에 관한 실험적 연구)

  • Kim, Young-Seok;Oka, Fusao
    • Journal of the Korean Geotechnical Society
    • /
    • v.24 no.1
    • /
    • pp.25-35
    • /
    • 2008
  • It has been recognized that the behaviour of unsaturated soil plays an important role in geomechanics. However, up to now, only a few experimental data are available for the technical difficulties related to both volume changes and suction measurements. In this study, the volume changes of unsaturated compacted silty soil were monitored with proximeter during various triaxial compression tests, which gave a realistic estimation in the volume changes of unsaturated soil sample. From the test results, the behaviours of wetting-induced collapses are observed during the drainage/water absorption tests. Under exhausted-drained conditions during shearing, the shear strength increases with an increasing initial suction. On the other hand, the volume changes become small with an increase in the initial suction. And, the volumetric strain during shearing is independent of the confining pressure.

Numerical Analysis of Stress-Strain Behavior of Geofoam (지오폼의 응력-변형률 거동의 수치적 해석)

  • Chun, Byung-Sik;Lim, Hae-Sik;Ahn, Tae-Bong;Lee, Cheol-Kyu
    • Journal of the Korean Geotechnical Society
    • /
    • v.16 no.3
    • /
    • pp.77-88
    • /
    • 2000
  • 연약지반상에 하중 경감을 목적으로 발포성 폴리스티렌(Expanded Polystyrene)을 사용하는 사례가 최근 꾸준히 증가하고 있다. 공법의 요점은 연약지반상에 축조되는 상부구조물에 의한 응력증가를 감소시켜서 결국에는 침하를 방지하기 위한 것이다. 이것을 지오폼(geofoam)이라고 하는데, 지오폼은 교대나 옹벽의 뒷채움재로 사용할 경우 횡토압을 감소시키기 때문에 옹벽이나 교대의 뒷채움재료로 사용하기도 한다. 이와 같이 그 사용이 꾸준히 증가하고 있지만 뒷채움이나 연악지반상에 사용할 때 지오폼의 거동을 예측하는 적절한 수치모델이 아직은 개발되자 않았다. 본 연구에서는 지오폼의 응력-변형 특성을 연구하고 그 탄소성 예측모델을 제시하였다. 이를 위하여 삼축압축시험을 실시하였으며 구속응력과 지오폼의 밀도를 다양하게 변화시켜 그 응력-변형특성을 조사하고 회귀분석을 통하여 비선형 구성모델을 제시하였다. 그 결과 지오폼은 탄성 선형모델보다 탄소성모델 특성에 더 가까운 것을 알 수 있었으며 체적변화율과 축방향 변형률에는 특별한 상관 관계가 있음을 알 수 있었다.

  • PDF

Effects of Hihh Amplitude Prestraining Vibrations on Shear Modulus of Sands (고 변형률 반복 진동이 모래의 전단 탄성계수에 미치는 영향)

  • ;Stokoe, K.H.Il
    • Geotechnical Engineering
    • /
    • v.8 no.1
    • /
    • pp.19-28
    • /
    • 1992
  • Recently, testing equipment which can run resonant column test altogether with the torsional shear test at the very highly controlled condition was developed at the University of Texas at Austin(U.S.A). With this equipment, the effects of high amplitude pre-straining vibrations on the dynamic properties of clean sands were studied. Tests showed the following results. Low amplitude shear modulus was gradually increased with little void ratio change as the number of high amplitude vibration cycles increased. Variation of volumetric strain with confining pressure for the pre -strained specimen under vibration was smaller than that of fresh specimen. Also the slope of the diagram for shear modulus and confining pressure relationship of the prestrained specimen was smaller than that of fresh specimens. These results agreed well with the analytical results.

  • PDF

Strain-Softening Behavior of Circular Tunnel Excavated in Mohr-Coulomb Rock Mass (Mohr-Coulomb 암반에 굴착된 원형 터널의 변형률연화 거동해석)

  • Lee, Youn-Kyou
    • Tunnel and Underground Space
    • /
    • v.16 no.6 s.65
    • /
    • pp.495-505
    • /
    • 2006
  • Calculating the distribution of stresses and displacements around a circular tunnel excavated in infinite isotropic rock mass subjected to hydrostatic stress condition is one of the basic problems in rock engineering. While closed-form solutions for the distribution are known if rock masses are considered as elastic, perfectly plastic, or brittle-plastic media, a few numerically approximated solutions based on various simplifying assumptions have been reported for strain-softening rock mass. In this study, a simple numerical method is introduced for the analysis of strain-softening behavior of the circular tunnel in Mohr-Coulomb rock mass. The method can also applied to the analysis of the tunnel in brittle-plastic or perfectly plastic media. For the brittle-plastic case where closed-formsolution exists, the performance of the present method is verified by showing an excellent agreement between two solutions. In order to demonstrate the strain-softening behaviors predicted by the proposed method. a parameter study for a softening index is given and the construction of ground reaction curves is carried out. The importance of defining the characteristics of dilation in plastic analysis is discussed through analyzing the displacements near the surface of tunnel.