• Proceedings of the KSME Conference
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• 2005.11a
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• pp.153.2-153.2
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• 2005

• Geotechnical Engineering
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• v.8 no.1
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• pp.19-28
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• 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.

• Tunnel and Underground Space
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• v.19 no.2
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• pp.158-166
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• 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.

• Journal of the Korea Concrete Institute
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• v.20 no.2
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• pp.221-229
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• 2008

An improved unbonded-type column strengthening procedure using wire rope and T-shaped steel plate units was proposed. Eight strengthened columns and an unstrengthened control column were tested under concentric axial load. The main variables considered were the volume ratio of wire rope and the flange width and configuration of T-shaped steel plates. Axial load capacity and ductility ratio of columns tested were compared with predictions obtained from the equation specified in ACI 318-05 and those of conventionally tied columns tested by Chung et al., respectively. In addition, a mathematical model was proposed to evaluate the complete stress-strain relationship of concrete confined by the wire rope and T-plate units. Test results showed that the axial load capacity and ductility of columns increased with the increase of the volume ratio of wire rope and the flange width of T-plates. In particular, at the same lateral reinforcement index, a much higher ductility ratio was observed in the strengthened columns having the volume ratio of wire rope above 0.0039 than in the tied columns. A mathematical model for the stress-strain relationship of confined concrete using the proposed strengthening procedure is developed. The predicted stress-strain curves were in good agreement with test results.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.11a
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• pp.533-538
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• 2000

Ductile fracture of dual phase steel begins with void nucleation, at martensite-ferrite interface of deformed martensite particle. In this study, void nucleation, growth, and coalescence under various strain were studied in dual phase steel. Therefore, by means of the heat treatment of low carbon steel, the study deals with void nucleation and growth for ferrite grain size and martensite volume fraction of dual phase steel using statistical method. Void nucleation and growth with increasing strain are shown depend upon the ferrite grain size. Voids volume fraction generally increase as ferrite grain size decease.

• Journal of the Korean Geotechnical Society
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• v.20 no.6
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• pp.75-83
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• 2004

This study is focused on the constitutive model in order to represent brittleness and dilatancy of cohesionless soils. The constitutive model was proposed on the basis of an anisotropic hardening rule with generalized isotropic hardening rule. The shape of yield surface is a simple cylinder type in stress space and it makes the model practically useful. Flow rule was approximated by a concrete function on dilatancy. A peak stress ratio was defined to model brittle stress-strain relationships. The proposed model was formulated and implemented to calculate the stress-strain relationship from triaxial tests. In the companion paper the proposed model will be verified by comparison with the triaxial test results.

• Journal of the Korean Geotechnical Society
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• v.23 no.3
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• pp.41-50
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• 2007

The results from normally consolidated isotropic drained and undrained triaxial compression tests (NCIU and NCID) on sand with high silt content were presented in this paper. The experiments were performed on specimens of Nak-dong River sand with 63% silt content under effective confined pressures, 100 kPa to 400 kPa. From test results, Sandy silt became initially compressive but eventually appeared to provide dilatancy response throughout the entire stress-strain curve The behavior of sandy silt was more difficult to characterize than that of clay and sand due to lower plastic characteristic. Especially, the samples exhibited dilatancy development during shear after failure. The shear behavior and shear strength parameters of sandy silt can be determined as stress-strain behaviors are described by the Mohr-Coulomb failure criterion. The shear behaviors were observed increasing dilatancy volume change tendency with strain-softening tendency after failure. In this paper, the behavior of dilatancy depends on not only sand content but also fine content with low-cohesion during shear in the samples of sandy silt.

• Journal of the Korean Geotechnical Society
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• v.16 no.3
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• pp.77-88
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• 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.

• Journal of the Korean Wood Science and Technology
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• v.37 no.3
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• pp.231-238
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• 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.

• Composites Research
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• v.26 no.4
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• pp.235-244
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• 2013

A volume integral equation method (VIEM) is introduced for the solution of elastostatic problems in an unbounded isotropic elastic solid containing multiple isotropic elliptical fibers of arbitrary orientation subject to uniform stress at infinity. The fibers are assumed to be long parallel elliptical cylinders composed of isotropic elastic material perfectly bonded to the isotropic matrix. The solid is assumed to be under plane strain on the plane normal to the cylinders. A detailed analysis of the stress field at the matrix-fiber interface for square and hexagonal packing of the fibers is carried out for different values of the number, orientation angles and concentration of the elliptical fibers. The accuracy and efficiency of the method are examined through comparison with results obtained from analytical and finite element methods.