• Proceedings of the Computational Structural Engineering Institute Conference
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• 2001.04a
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• pp.335-342
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• 2001

In this paper, an improved Element-Free Galerkin (EFG) method is proposed by adding enrichment function to the standard EFG approximation and a discontinuity function is implemented in constructing the shape function across the crack surface. In this method, the singularity and the discontinuity of the crack are efficiently modeled by using initial node distribution to evaluate reliable stress intensity factor, though the standard EFG method requires placing additional nodes near the crack tip. The proposed method enables the initial node distribution to be kept without any additional nodal d.o.f. and expresses the asymptotic stress field near the crack tip successfully. Numerical example verifies the improvement and the effectiveness of the method.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.5A
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• pp.649-656
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• 2008

The enhancement of the service life of damaged or cracked structures is a major issue for researchers and engineers. The hierarchic void element based on the integrals of Legendre polynomials is used to characterize the fracture behaviour of unpatched crack as well as repaired crack with bonded composite patches by computing the stress intensity factors and stress contours at the crack tip. Since the equivalent single layer approach is adopted in this study, the proposed element is necessary to represent a discontinuous crack part as a continuum body with zero stiffness. Thus the aspect ratio of this element to represent the crack should be extremely slender. The sensitivity of numerical solution with respect to energy release rate, displacement and stress has been tested to show the robustness of zero stiffness element as the aspect ratio is increased up to 2000. The stiffness derivative method and displacement extrapolation method have been applied to calculate the stress intensity factors of Mode I problem. It is noted that the proposed hierarchical void element can be one of alternatives to analyze the patched crack problems.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1993.05a
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• pp.96-99
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• 1993

Electrical properties of the Thin Film Transistor(TFT) electrode metal films were investigated through the Test Elements Group(TEG) experiment. The main purpose of this investigation was to characterize the electrical resistance properties of patterned metal films with respect to the variations of film thickness and TEG metal line width. Aluminum(Al), Tantalum(Ta) and Chromium(Cr) that are currently used as TFT electrode films were selected as the probed metal films. To date, no work in the electrical characterizations of patterned electrodes of a-Si TFT was accomplished. Bulk resistance$(R_b)$, sheet resistance$(R_s)$, and resistivities($\rho$) of TEG patterned metal lines were obtained. Electrical continuity test of metal film lines was also performed in order to investigate the stability of metallization process. Almost uniform-linear variations of the electrical properties with respect to the metal line displacements was also observed.

• Journal of the Korean Society for Railway
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• v.13 no.5
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• pp.521-527
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• 2010

The Paved Track is applied to reduce maintenance cost of conventional line. The Paved Track could be used in all types of lines including earthwork, bridge, tunnel and turnout sections. In case of earthwork section, the construction joint is the most critical factor to track durability. The construction joint does not affect to the track structure directly, but the gap due to discontinuity of slabs may affect to the long-term serviceability. To evaluate this problem, the accelerated track test has been performed on the construction joint and the middle part to of the real scale Paved Track. The purpose of this test is that evaluate the vulnerability of construction joint section comparing the trends of settlement and earth pressure under repeated loads of construction joint with those of the middle slab part.

• Proceedings of the Korean Society for Rock Mechanics Conference
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• 2000.09a
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• pp.117-128
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• 2000

The development of proper joint model, which can describe real phenomena exactly and still can be used easily, is one of the most important element for the analysis of the mechanical and hydraulic behavior of discontinuous rock mass. In this study, an elasto-plastic constitutive model of joint behavior considering asperity degradation was extended with the concept of first and second order asperities. The proposed model was implemented to numerical code with discrete finite joint element. The parametric study with the various asperity angles and degradation coefficients showed that the model can reproduce the shear behavior of typical rough joints well. Results of laboratory monotonic and cyclic shear tests were compared with those of numerical tests to validate the model. The hydraulic model considering the relations between gouge production and aperture was introduced to the mechanical model. In an attempt to examine the performance of the model, comparative numerical test was conducted. Permeability between joint surfaces increased rapidly at the first stage, but became nearly constant with increasing shear displacement due to gouge production and uniform variation of aperture distribution.

• Tunnel and Underground Space
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• v.10 no.3
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• pp.366-377
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• 2000

The development of proper joint model, which can describe real phenomena exactly and still can be used easily, is one of the most important element for the analysis of the mechanical and hydraulic behavior of discontinuous rock mass. In this study, an elasto-plastic constitutive model of joint behavior considering asperity degradation was extended with the concept of first and second order asperities. The proposed model was implemented to numerical code with discrete finite joint element. The parametric study with the various asperity angles and degradation coefficients showed that the model can reproduce the shear behavior of typical rough joints well. Results of laboratory monotonic and cyclic shear tests were compared with those of numerical tests to validate the model. The hydraulic model considering the relations between gouge production and aperture was introduced to the mechanical mode1. In an attempt to examine the performance of the model, comparative numerical test was conducted. Permeability between joint surfaces increased rapidly at the first stage, but became nearly constant with increasing shear displacement due to gouge production and uniform variation of aperture distribution.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.26 no.1
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• pp.79-87
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• 2013

An isogeometric topological shape optimization method is developed using the level sets and Heaviside enrichments. In the level set method, the initial domain is kept fixed and its boundary is represented by an implicit moving boundary embedded in the level set functions, which facilitates to handle complicated topological shape changes. The Heaviside enrichment improves the isogeometric analysis by adding some enrichment functions to model the internal boundaries. The proposed topological shape optimization method has several benefits: exact geometric models can be obtained using the isogeometric approach and the limitation of tensor-product patches can be overcome using the Heaviside enrichments to represent the internal voids. Even in a single patch, discontinuous displacement fields as well as smooth stress field can be obtained. Since the level sets offer the implicit moving boundary inside the domain, it is easy to represent the topological shape variations in the isogeometric analysis using Heaviside enrichments.

• Tunnel and Underground Space
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• v.29 no.3
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• pp.197-213
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• 2019

We simulated the fault reactivation experiment conducted at 'Main Fault' intersecting the low permeability clay formations of Mont Terri Underground Research Laboratory in Switzerland using TOUGH-FLAC simulator. The fluid flow along a fault was modelled with solid elements and governed by Darcy's law with the cubic law in TOUGH2, whereas the mechanical behavior of a single fault was represented by creating interface elements between two separating rock blocks in FLAC3D. We formulate the hydro-mechanical coupling relation of hydraulic aperture to consider the elastic fracture opening and failure-induced dilation for reproducing the abrupt changes in injection flow rate and monitoring pressure at fracture opening pressure. A parametric study was conducted to examine the effects of in-situ stress condition and fault deformation and strength parameters and to find the optimal parameter set to reproduce the field observations. In the best matching simulation, the fracture opening pressure and variations of injection flow rate and monitoring pressure showed good agreement with field experiment results, which suggests the capability of the numerical model to reasonably capture the fracture opening and propagation process. The model overestimated the fault displacement in shear direction and the range of reactivated zone, which was attributed to the progressive shear failures along the fault at high injection pressure. In the field experiment results, however, fracture tensile opening seems the dominant mechanism affecting the hydraulic aperture increase.

• Journal of the Earthquake Engineering Society of Korea
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• v.6 no.3
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• pp.31-40
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• 2002

The purpose of this study is to investigate the seismic behavior of RC bridge piers and to provide the data for developing improved seismic design criteria. The accuracy and objectivity of the assessment process may be enhanced by the use of sophisticated nonlinear finite element analysis program. A computer program, named RCAHEST(reinforced concrete analysis in higher evaluation system technology), for the analysis of reinforced concrete structures was used. Material nonlinearity is taken into account by comprising tensile, compressive and shear models of cracked concrete and a model of reinforcing steel. The smeared crack approach is incorporated. n boundary plane at which each member with different thickness is connected, local discontinuity in deformation due to the abrupt change in their stiffness can be taken into account by introducing interface element. The effect of number of load reversals with the same displacement amplitude has been also taken into account to model the reinforcing steel and concrete. In the companion paper, the proposed numerical method for seismic damage evaluation of RC bridge piers is verified by comparison with the reliable experimental results.

• Journal of the Earthquake Engineering Society of Korea
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• v.6 no.1
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• pp.23-31
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• 2002

The purpose of this study is to investigate the size effect on inelastic behavior of reinforced concrete bridge piers. A computer program, named RCAHEST(reinforced concrete analysis in higher evaluation system technology), for the analysis for reinforced concrete structures was used. Material nonlinearity is taken into account by comprising tensile, compressive and shear models of cracked concrete and a model of reinforcing steel. The smeared crack approach is incorporated. In boundary plane at which each member with different thickness is connected, local discontinuous deformation due to the abrupt change in their stiffness can be taken into account by introducing interface element. The effect of number of load reversals with the same displacement amplitude has been also taken into account to model the reinforcing steel. To determine the size effect on bridge pier inelastic behavior, a 1/4-scale replicate model was also loaded for comparison with the full-scale bridge pier behavior.