• Journal of the Earthquake Engineering Society of Korea
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• v.12 no.1
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• pp.43-55
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• 2008

The complexity of determining strain associated with shear modulus and damping ratio in torsional tests has been resolved by means of several approaches. Particularly, the modified equivalent radius approach is adequate to when generating the plots of equivalent radius ratio versus strain more effectively over any range of strains in resonant column and torsional shear (RC/TS) tests. The modified equivalent radius approach was applied for hyperbolic, modified hyperbolic, and Ramberg-Osgood models in evaluating damping ratio. Results showed that using a single value of equivalent radius ratio based on conventional equivalent radius approach is not appropriate. A new model was developed to consider the soil damping behavior at small strains as well as hysteretic damping and it was attempted to determine adjustments are required in evaluating strain associated damping when combining the two damping components.

• Magazine of the Korea Concrete Institute
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• v.9 no.5
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• pp.115-125
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• 1997

콘크리트의 변형률국소화는 콘크리트의연화거동에 수반되어 변형이 국부적으로 집중되는 현상이다. 본 연구의 목적은 인장과 압축하중상태에서 콘크리트 부재에 발생하는 콘크리트 변형률 국소화 거동을 해석적으로 재현할 수 있는 통일된 모형을 제안하는 것이다. 본 논문에서는 인장과 압축에 대하여 변형률국소화가 일어나는 콘크리트 부재를 변형률 연화가 일어나는 국소화영역과 탄성제하가 발생하는 비국소화영역으로 구분하여 모델링하는 통일된 모형을 제안하였다. 또한 제안된 모형에서 미시역학적 평균화기법을 이용해 평균등가탄성계수와 수정된 평균등가탄성계수를 구하여 시편의 크기와 국소화영역의 크기에 따는 해석을 수행하였으며 기존의 실험값과 비교하였다. 연구결과, 본 연구에서의 변형률국소화모형이 크기효과를 포함한 콘크리트의 변형률국소화거동 해석에 타당하게 적용될 수 있음을 보여주었다.

• Journal of the Korean Geotechnical Society
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• v.16 no.5
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• pp.5-17
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• 2000

등가선형이론을 이용한 지진응답해석은 사용의 간편함 때문에 많이 사용되고 있지만, 대부분의 입력 정수들이 경험식에 의해 얻어지고 있어 심각한 오류를 발생시킬 여지가 있다. 입력정수를 실험의 결과로부터 얻을수 없다면 합리적인 방법을 통하여 입력 정수를 결정하여야 하며, 또한 입력 정수들이 해석결과에 어떠한 영향을 미치는지에 대한 고찰이 필요하다. 따라서 본 연구에서는 입력정수가 해석결과에 미치는 영향에 대한 민감도 분석을 실시하였다. 해석은 등가선형화 이론에 기초하여 개발한 액상화 해석프로그램(KLIq)을 이용하였다. 검토된 사항은 전단탄성계수와 감쇠비의 영향, 변형률의 영향, 반복계산에서 유효변형률 결정방법, 최대전자탄성계수의 영향, 변형률 의존곡선(자반의 종류)의 영향, 입력 지질파의 영향 등이다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.5
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• pp.337-343
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• 2017

As a shop practice, a strength estimation method for die cast parts is suggested, in which various defects such as pores can be allowed. The equivalent porosity is evaluated by combining the stiffness data from a simple elastic test at the part level during the shop practice and the theoretical stiffness data, which are defect free. A porosity equation is derived from Eshelby's inclusion theory. Then, using the Mori-Tanaka method, the porosity value is used to draw a stress-strain curve for the porous material. In this paper, the Hollomon equation is used to capture the strain hardening effect. This stress-strain curve can be used to estimate the strength of a die cast part with porous defects. An elastoplastic theoretical solution is derived for the three-point bending of a die cast beam by using the plastic hinge method as a reference solution for a part with porous defects.

• Journal of the Korea Concrete Institute
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• v.26 no.4
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• pp.555-562
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• 2014

To perform performance-based seismic design of buildings, it is necessary clear goal for usage and stability after an earthquake. To clear this goal, it requires a review of the constituent material of the building and, in particular, a member used as an indicator of the residual strain is useful. There are more usage of prestressed concrete because of prestressing steel witch has characteristics of the origin-oriented. In this study, the goal is estimating of residual strain on the prestressed concrete beam member. The expression for angle of deformed prestressed concrete beam member was obtained from using of curvature on the critical section and the equivalent plastic hinge length based on 'equivalent plastic hinge length method'. Considering the balance of strength and deformation conditions, suitable analysis values were derived from 'split Element Method'. Through various parametric studies, various factors affecting the residual strain were decided. Based on the results of this study, it is expected many researches will be proceed in the future.

• Journal of the Korean GEO-environmental Society
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• v.11 no.6
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• pp.5-20
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• 2010

One-dimensional equivalent linear site response analysis is widely used in practice due to its simplicity, requiring only few input parameters, and low computational cost. The main limitation of the procedure is that it is essentially a linear method, in which the time dependent change in the soil properties cannot be modeled and constant values of shear modulus and damping is used throughout the duration of the analysis. Various forms of modified equivalent linear analyses have been developed to enhance the accuracy of the equivalent linear method by incorporating the dependence of the shear strain with the loading frequency. The methods are identical in that it uses the shear strain Fourier spectrum as the backbone of the analysis, but differ in the method in which the strain Fourier spectrum is smoothed. This study used two domestically measured soil profiles to perform a series of nonlinear, equivalent linear, and modified equivalent linear site response analyses to verify the accuracy of two modified procedures. The results of the analyses indicate that the modified equivalent linear analysis can highly overestimate the amplification of the high frequency components of the ground motion. The degree of overestimation is dependent on the characteristics of the input ground motion. Use of a motion rich in high frequency contents can result in unrealistic response.

• Journal of Korean Society of Steel Construction
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• v.9 no.3 s.32
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• pp.401-419
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• 1997

In this paper the kinematics of damage for finite strain, elasto-plastic deformation is introduced using the fourth-order damage effect tensor through the concept of the effective stress within the framework of continuum damage mechanics. In the absence of the kinematic description of damage deformation leads one to adopt one of the following two different hypotheses for the small deformation problems. One uses either the hypothesis of strain equivalence or the hypotheses of energy equivalence in order to characterize the damage of the material. The proposed approach in this work provides a general description of kinematics of damage applicable to finite strains. This is accomplished by directly considering the kinematics of the deformation field and furthermore it is not confined to small strains as in the case of the strain equivalence or the strain equivalence approaches. In this work, the damage is described kinematically in both the elastic domain and plastic domain using the fourth order damage effect tensor which is a function of the second-order damage tensor. The damage effect tensor is explicitly characterized in terms of a kinematic measurure of damage through a second-order damage tensor. Two kinds of second-order damage tensor representations are used in this work with respect to two reference configurations.

• Geotechnical Engineering
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• v.12 no.6
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• pp.127-138
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• 1996

The in-situ consolidation behavior of drainage system-installed deposits has three dimensional characteristics. Therefore, for an approximate 2-D plane strain consolidation analysis, it is necessary to convert the 3-D spatial flow of actual cases into the laminar flow simulated by the 2-D plane strain model. . In this paper, in order to properly model the effect of three dimensional characteristics, an equivalent and efficient model has been applied in a finite element technique for the analysis of the drainage system-installed soil deposits. The equivalent two dimensional model involves equivalent permeabilities and drainage widths. To validate the equivalent two dimensional model, three dimensional analyses were per formed by using the ABAQUS program and the results of 3-D analyses were compared with those of the 2-D analyses. By using the proposed equivalent model, one may be able to appropriately predict the consolidation behavior of drainage system-installed soft deposits.

• Composites Research
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• v.17 no.6
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• pp.8-13
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• 2004

A new three-dimensional model fur stress-strain relation of a porous shape memory alloy has been proposed, where Eshelby's equivalent inclusion method with Mori-Tanaka's mean field theory is used. The predicted stress-strain relations by the present model are compared and show good agreements with the experimental results for the Ni-Ti shape memory alloy with porosity of 12%. Unlike linear stress-strain relations during phase transformations by other models from the literature, the present model shows nonlinear stress-strain relation in the vicinity of martensite finish region.

• Proceedings of the Korean Society for Rock Mechanics Conference
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• 2000.09a
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• pp.139-146
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• 2000

This study investigates the changes of subsidence and hydraulic conductivity by underground mining. Coupling between post-mining induced strains and strain-dependent hydraulic conductivities is obtained by idealizing a jointed rock mass as an equivalent porous medium in which the hydraulic conductivity of a single joint is defined through parallel plate description. Results indicate that post-mining hydraulic conductivities are directly related to the strain field occurred by subsidence induced deformation. Maximum subsidence and hydraulic conductivity values increase as a panel width does widen. Joint spacing has an effect on the intensity of the changes in hydraulic conductivity.