• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.3
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• pp.543-552
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• 1994

A series of drained plane strain compression tests was performed on dried samples of dense Toyoura sand and Silver Leighton Buzzard sand prepared by air-pluviation method to find out the deformation and strength characteristics on the value of confining pressure ${\sigma}{_3}^{\prime}({\sigma}{_3}^{\prime}=0.05{\sim}4.0kgf/cm^2)$. The axial and lateral strains measured in this apparatus ranged from $10^{-6}$ up to the failure of the specimen. So the stress-strain characteristics would be investigated from very small to very large strain levels. It was found that the change of the angle of internal friction ${\phi}^{\prime}{_{max}}=arcsin\{({\sigma}{_1}^{\prime}-{\sigma}{_3}^{\prime})/({\sigma}{_1}^{\prime}+{\sigma}{_3}^{\prime})\}_{max}$ with the change of ${\sigma}{_3}^{\prime}$ is very small when ${\sigma}{_3}^{\prime}$ is lower than higher. Furthermore, the effect of confining pressure on stiffness of sands was evaluated. It was also found that for the range of shear strain ${\gamma}$ from $10^{-6}$ to those at peak, the Rowe's stress-dilatancy relation seems to be a good approximation for air-dried Toyoura sand and Silver Leighton Buzzard sand, irrespective of the change of ${\sigma}{_3}^{\prime}$.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.10
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• pp.1057-1068
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• 2014

This paper proposes elastic-plastic constitutive relations for a composite material with two phases-inclusion and matrix phases-using a homogenization scheme. A thermodynamic framework is employed to develop non-local plasticity constitutive relations, which are specifically represented in terms of the second-order gradient terms of the internal state variables. A combined two back-stress evolution equation is also established and the degradation of the state and internal variables is expressed by continuum damage mechanics in terms of the damage factor. Then, deformation localization is analyzed; the analysis results show that the proposed model yields a wide range of shear band formation behaviors depending on the evolution of the specific internal state variables. The analysis results also show good agreement with the results of simplified Rice instability analyses.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.4
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• pp.425-431
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• 2015

Based on a bond-based peridynamics theory for dynamic crack propagation problems, this paper presents a design sensitivity analysis and optimization method. Peridynamics has a peculiar advantage over the existing continuum theory in the mathematical modelling of problems where discontinuities arise. For the design optimization of the crack propagation problems, a non-shape design sensitivity is derived using the adjoint variable method. The obtained adjoint sensitivity of displacement and strain energy turns out to be very accurate and efficient compared to the finite different sensitivity. The obtained design sensitivities are futher utilized to optimally control the position of bifurcation point in the design optimization of crack propagation in a plate under tension. A numerical experiment demonstrates that the optimal distribution of material density could delay the position of bifurcation.

• Journal of the Korean GEO-environmental Society
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• v.2 no.3
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• pp.81-88
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• 2001

The behavior of porous medium is modeled by linear thermoporoelastic behavior, linear poroviscoelastic behavior, poroplastic behavior, and poroviscoplastic behavior, etc. The behavior has, in general, a complicated aspect which makes a mechanical description of the problem with time. Constitutive modeling for deformation behavior of porous medium with coupling effects is needed since there is interaction between the constituents in pores with a relative velocity to each other. In this work, it is explained 3-dimensional behavior depending on degree of saturation for porous medium composed of homogeneous, isotropic materials. It is obtained the governing equations based on continuum porous mechanics. In addition, it is developed constitutive model which can be understood of behavior for porous medium which can be understood, analysed behavior of porous medium. It can be accomplished exact analysis and prediction of behavior in porous medium. The behavior for porous medium is analysed exactly, and the prediction of deformation behavior is accomplished. Consequently, it will be basis to analyze 3-dimensional behavior in municipal solid waste landfill, and the practical using of porous medium ground which are composed of nonhomogeneous, anisotropic materials can be done widely.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.5
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• pp.2125-2133
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• 2013

Recently, an interest on joint behavior between adjacent concrete slab tracks has increasing due to large application of such track system. Dowel bars are widely used to improve load transfer capacity across the joints. Dowel bars reduce the deflections and stresses by transferring the load between the slabs. This study proposes the lumped shear spring model to efficiently model dowel joints of adjacent slabs. This model includes bearing stiffness between dowel bar and concrete as well as dowel gap. Strength of the proposed spring model is evaluated based on Concrete Capacity Design method under the assumption of shear failure mode in the joints. Experiments are also performed up to failure to evaluate the accuracy of the proposed model. It has been observed that the proposed model is able to predict initial nonlinearity due to dowel gap, and capture material nonlinearity of the test slabs. Thus, it is recommended that the proposed model can be effectively applied to the dowel joints of concrete slab track.

• Journal of Korean Tunnelling and Underground Space Association
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• v.9 no.4
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• pp.323-330
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• 2007

Recently, due to the effective land utilization and environmental protection, the construction of 2-arch tunnel has been gradually increased. In spite of this tendency, the mechanical information for the 2-arch tunnel, especially such as its behavior characteristics and mechanism are not enough. Therefore in this study, the theoretical and numerical studies on the behavior characteristics of 2-arch tunnel are carried out and longitudinal optimum separated distance of tunnel face is proposed by considering the analysis results from the behavior of advanced excavation of tunnel and stress of central pillar. As a result, longitudinal optimum separated distance of tunnel face is in 0.5D for the better safety of 2-arch tunnel by rapidly decreasing the stress concentration of central pillar.

• Journal of Korean Tunnelling and Underground Space Association
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• v.16 no.1
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• pp.91-104
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• 2014

An Excavation Damaged Zone (EDZ), in which rock properties are permanently changed due to blasting impact or stress redistribution, can influence the behavior and stability of structures. In this study, the mechanical stability of an underground opening was simulated by using FLAC, which is a two-dimensional modeling code, with a consideration of EDZ. A sensitivity analysis was also carried out with fractional factorial design. From the modeling, it was found that the behavior and the stability of an underground tunnel are strongly dependent on the existence of the EDZ. The sensitivity analysis showed that the key parameters affecting the factor of safety around the tunnel are in-situ stress ratio, depth, cohesion, reduction ratio, internal friction angle, and height and width of the tunnel. It is necessary to consider the EDZ, which can significantly affect mechanical stability in tunnel design.

• Elastomers and Composites
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• v.34 no.3
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• pp.229-238
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• 1999

In this study, double bond, unsaturated group was introduced to the main chain of EVA by chemically treating EVA, nondiene polymer. Benzene sulfonic acid, ENB and DCPD were used as a third element. Also, from blending CR and SBR, conventional synthetic rubber we prepared vulcanizates and examined their physical properties. The datum lead to the following conclusion that some problems were modified; limited temperature in use and mechanical properties like hardness, tensile strength, tensile stress, and elongation rate of thermoplastic EVA, keeping the following advantages of original EVA; green strength, injection molding by Pressure, adhesion, tackiness, dimensional stability, and ozone resistance, etc. It is expected that continuous research of the modification between nondiene and diene polymer will improve what were shown disadvantages in synthetic polymer; processing, oxidation resistance, and adhesion. In addition, it will be possible to continue process of rubber products by utilizing possible fluidity for fusion of EVA.

• Geotechnical Engineering
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• v.14 no.4
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• pp.17-32
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• 1998

has been much progress in theories and construction techniques to secure the stability of the underground structures. Recently, several studios have shown that it is possible to predict the existence of discontinuities ahead of a tunnel face by analyzing 3-dimensional absolute displacements measured during tunnel excavation. This paper concentrated on the development of a methodology to predict the existence and location of the discontinuities, or the void space(abandoned mine) , by performing 3-dimensional FEM analysis and considering the stress relocation caused by arching effect during excavation. Also, this study tried to verify deformation for choosing the most suitable support system. The results of this study might provide a way of safer and economical tunnel construction by utilizing the in-situ monitoring data.

• Journal of the Earthquake Engineering Society of Korea
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• v.6 no.3
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• pp.1-10
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• 2002

A series of unreinforced masonry(URM) walls were analytically investigated by FEM for a limited version of seismic in-plane performance. For this, URM walls were assumed to be continum and modeled as isotropic plane stress elements, within which the nature of cracking was propogated. Accordingly, behavioral mode of cracking in URM was modeled by smeared-crack approach. Total of 70 cases were considered for various parameters such as axial load ratio, aspect ratio and effective section area ratio due to the existence of opening, etc. The analysis results indicate that these parameters significantly and interactively influence over the ultimate strength of URM walls. Finally, it is suggested that the response modification factor for URM adopted in the current Korean Standard should be validated considering various forms of brittleness and probable failure modes in URM.