• Tunnel and Underground Space
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• v.19 no.6
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• pp.498-506
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• 2009

The stability assessment of a concrete liner of a compressed air storage tunnel should be performed by an approach which is different from that commonly used for the liners of road tunnels, since the liner is exposed to high air pressure. In this study, the stability analysis method for the liner of compressed air storage tunnel is proposed based on the elastic and elasto-plastic solutions of the thick-walled cylinder problem. In case of elastic analysis, the yield initiation condition at the inner boundary is considered as the failure condition of the liner, while the condition which results in the extension of yielding zone to a certain depth is taken as a failure indicator of the liner in the elasto-plastic analysis taking Mohr-Coulomb criterion. The application of the proposed method revealed that the influence of the relative magnitude of boundary loads on the stability of liner is considerable. In particular, noting that the estimation of the outer boundary load may be relatively difficult, it is thought that the precise prediction of outer boundary load is very important in the analysis. Accordingly, the emphasis is put on the selection of the liner installation time, which may govern the magnitude of outer boundary load.

• Tunnel and Underground Space
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• v.12 no.4
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• pp.248-258
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• 2002

The sixth underground pumped powerhouse cavern is now under construction in Korea. For the stability analysis for the caverns of the five underground powerhouses, finite element method was used. For the analysis, in-situ rock stress were measured by overcoring method. The stress measurement showed that initial horizontal to vertical stress ratio was 1.07-1.32 in low powerhouse sites. Rock mass strength and elasticity were assumed from rock core properties through engineering processes. So the ratio of input elasticity fur the analysis were about 0.16-0.55 to rock core elasticity. In most of the analysis, elasto-plastic condition with Mohr-Coulomb failure criteria were applied. But in one case, viscoelastic condition was applied, too. The input cohesion and internal friction angle were approximately 0.12-0.22, 0.6-0.87 to rock core strength parameters, respectively.

• Journal of the Korean GEO-environmental Society
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• v.16 no.10
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• pp.5-14
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• 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.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.6 no.4
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• pp.108-117
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• 1997

A continuum analysis has been performed for the application to the thermo-elasto-plastic behavior in a discontinuous metal matrix composite. an FEM (Finite Element Method) analysis was implemented to obtain the internal field quantities of composite as well as overall composite behavior and an experiment was demonstrated to compare with the numerical simulation . As the procedure, a reasonably optimized FE mesh generation, the appropriate imposition of boundary condition , and the relevant post processing such as elastoplastic thermomchanical analysis were taken into account. For the numerical illustration, an aligned axisymmetric single fiber model with temperature dependent material properties and precipitation hardening effect has been employed to assess field quantities. It was found that the residual stresses are induced substantially by the temperature drop during the thermal treatment and that the FEM results of the vertically and horizontally constrained model give a good agreement with experimental data.with non-woven carbon mat is about 24% higher than that of composite materials without non-woven carbon mat. Transverse tensile strength and torughness also increase by inserting non-woven carbon mat between layers.

• Journal of the Society of Naval Architects of Korea
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• v.45 no.1
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• pp.93-100
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• 2008

There are two ways of conventional thermal distortion analysis. One is the thermal elasto-plastic analysis and the other is the equivalent forces method based on inherent strain. The former needs exorbitant analysis time, while the latter cannot obtain results of stress field and it needs much time consumption with loads modeling on curved plates. Such faults in two methods have made difficulties in thermal distortion analysis of a large structure like ship hull. In order to solve them, new kind of thermal distortion analysis method was developed. We devised that the inherent strains was used as direct input factors in forms of boundary conditions. It was embodied by using thermal expansion coefficient in commercial code. We used the pre-calculated inherent strain as thermal expansion coefficient, and endowed nodes with imaginary temperatures. This method was already adopted at hull block welding distortion analysis which was considered as impossible, and gave productive results such as reduction of work time in the dry dock.

• Journal of Ocean Engineering and Technology
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• v.15 no.2
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• pp.72-78
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• 2001

The bead is used to provide properly restraining force in the sheet metal forming process. This bead process includes bending and geometrical non-linearity, and affects the state of binderwrap. Therefore, the analysis of bead process is very important to obtain the desired formability. In this paper, the research about the influence of the punch stroke of bead on the draw-bead process was conducted. Results from the analysis will give useful information to the effective tool design of blank forming process. To analyze the bead process, and elasto-plastic finite element formulation is constructed from the equilibrium equation and the considered boundary conditions involved a proper contact condition. The static-explicit finite element method as a numerical method for the analysis was applied to the analysis program code. It was found that this method could solve too much computation time and convergence problem owing to high non-linearity of bead forming process.

• Structural Engineering and Mechanics
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• v.4 no.6
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• pp.645-653
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• 1996

In order to avoid pathological mesh dependency in finite element modelling of strain localization, an isotropic elasto-plastic model with a yield function depending on the Laplacian of the equivalent plastic strain is implemented in a 4-node quadrilateral finite element with one integration point based on a mixed formulation derived from Hu-Washizu principle. The evaluation of the Laplacian is based on a least square polynomial approximation of the equivalent plastic strain around each integration point. This non local approach allows to satisfy exactly the consistency condition at each integration point. Some examples are treated to illustrate the effectiveness of the method.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.04a
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• pp.353-358
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• 1998

The strain localization is a discontinuous phenomenon that addresses the formation of jumps of the field variables across a singularity surface. It has become widely accepted that the localization may occur as the result of discontinuous bifurcation which corresponds to the loss of ellipticity of the governing differential equations for elasto-plastic continua. In this paper, condition for strain localization in concrete based on bifurcation theory is studied and localization tensor analysis algorithm is employed to determine the directions of localization of deformations in concrete. By applying a plasticity model of concrete into the algorithm, localization analysis is performed concrete under uniaxial tension, pure shear and uniaxial compression.

• Tunnel and Underground Space
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• v.18 no.2
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• pp.98-106
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• 2008

When a tunnel is excavated in a rock mass of poor condition, the adjacent zone of excavation surface may be reinforced by adopting the appropriate methods such as grouting and rock bolting. The reinforced effect can be evaluated by use of various numerical approaches, where the reinforcing elements may be expressed as distinct discretizations or smeared into the equivalent material properties. In this study, a simple numerical method, which can be classified as the latter approach, was developed for the elasto-plastic analysis of a circular tunnel. If a circular tunnel in a Mohr-Coulomb rock mass is reinforced to a finite thickness, the reinforced annulus may have different material properties from the in-situ rock mass. In the proposed elasto-plastic method for assessing the reinforcing effect, Lee & Pietruszczak (2007)'s method is applied to both the reinforced annulus and the outer insitu rock mass of the fictitious tunnel, and then two results are combined by enforcing the compatibility condition. The method were verified through comparing the results with the proposed method and the commercial finite difference code FLAC. When taking the variation of deformation modulus and strength parameters in the reinforced zone into account, the distributions of stress and radial displacement were much different from those obtained with the assumption of homogeneous rock mass.

• Structural Engineering and Mechanics
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• v.9 no.3
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• pp.241-256
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• 2000

The major sources of energy dissipation in steel frames with partially restrained (PR) connections are evaluated. Available experimental results are used to verify the mathematical model used in this study. The verified model is then used to quantify the energy dissipation in PR connections due to hysteretic behavior, due to viscous damping and at plastic hinges if they are formed. Observations are made for two load conditions: a sinusoidal load applied at the top of the frame, and a sinusoidal ground acceleration applied at the base of the frame representing a seismic loading condition. This analytical study confirms the general behavior, observed during experimental investigations, that PR connections reduce the overall stiffness of frames, but add a major source of energy dissipation. As the connections become stiffer, the contribution of PR connections in dissipating energy becomes less significant. A connection with a T ratio (representing its stiffness) of at least 0.9 should not be considered as fully restrained as is commonly assumed, since the energy dissipation characteristics are different. The flexibility of PR connections alters the fundamental frequency of the frame. Depending on the situation, it may bring the frame closer to or further from the resonance condition. If the frame approaches the resonance condition, the effect of damping is expected to be very important. However, if the frame moves away from the resonance condition, the energy dissipation at the PR connections is expected to be significant with an increase in the deformation of the frame, particularly for low damping values. For low damping values, the dissipation of energy at plastic hinges is comparable to that due to viscous damping, and increases as the frame approaches failure. For the range of parameters considered in this study, the energy dissipations at the PR connections and at the plastic hinges are of the same order of magnitude. The study quantitatively confirms the general observations made in experimental investigations for steel frames with PR connections; however, proper consideration of the stiffness of PR connections and other dynamic properties is essential in predicting the dynamic behavior.