• 한국강구조학회 논문집
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• 제9권1호통권30호
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• pp.51-63
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• 1997

Highly curved steel-box bridges are usually constructed as ramp structures for the highway interchange and metropolitan elevated highway junction, but a number of these bridges are deteriorated and damaged to a significant degree due to heavy traffic. The main objective of the study is to develop a practical reliability-based assessment of safety and residual load carrying-capacity of existing curved steel-box ramp bridges. In the paper, for the realistic assessment of safety and residual load carrying-capacity of deteriorated and/or damaged curved steel-box bridges, an interactive non-linear limit state model is formulated based on the von Mises's combined stress yield criterion. It is demonstrated that the proposed model is effective for the assessment of reliability-based safety and the evaluation of residual load carrying-capacity of curved steel-box bridges. In addition, this study comparatively shows the applicability of various reliability analysis methods, and suggests a practical and effective one to be used in practice.

• 소성∙가공
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• 제24권6호
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• pp.395-399
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• 2015

A microstructure-based finite element simulation was conducted to predict the plastic strain ratio (R-value) of a dual-phase (DP) steel. The representative volume elements (RVEs) concept was adopted for the image-based FE modeling and a 3D model was constructed using sequential 2D images. Each phase was considered with the von-Mises yield criterion and the Swift model. The Swift parameters were defined by the empirical equations based on the chemical composition. The developed model was applied to analyze the effect of residual stress on the R-value and stress distribution. In order to consider the residual stress development after cold rolling, 10 % compression was applied in the thickness direction and unloaded before the tensile stress was applied in the rolling direction. The results showed a reasonable prediction for the R-value evolution: a sharp increase at small strains was well described and a transition followed in the downward direction. The R-value evolution was analyzed using the stress distribution change on the π-plane

• Tribology and Lubricants
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• 제31권4호
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• pp.170-176
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• 2015

As a continuation of Part I, which developed a design formula of the minimum corner radius (R_min) for restraining tribological failures, Part II investigates design parameters such as material properties and contact force. As design examples, Al 7075-T651, SST 304 and HT-9 are chosen for the materials and 1, 10 and 100 kN are used for the forces. The results show that the difference in R_min decreases as either the elastic modulus increases or the contact force decreases. Given the same material and force, the permissible R_min decreases as the flat region increases and vice versa. Because the R_min values obtained from the examples are very small, the dimensions of the corner radius normally designed in engineering structures are regarded acceptable. The von Mises stress evaluated for a typical example, which is far below the yield strength, confirms this interpretation. Nevertheless, the present work can provide a design criterion as well as a guideline for quality control in the manufacturing of, in particular, contact corners, which has not been attempted before to the best of the author’s knowledge. In addition, this paper considers the problem of a step that may be formed in the contact contour by using a similar approach. The result shows that no size of the step is permissible.

• International Journal of Aeronautical and Space Sciences
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• 제2권2호
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• pp.65-72
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• 2001

This paper demonstrates an explicit-implicit, finite element analysis for linear as well as nonlinear hygrothermal stress problems. Additional features, such as moisture diffusion equation, crack element and virtual crack extension(VCE) method for evaluating J-integral are implemented in this program. The Linear Elastic Fracture Mechanics(LEFM) Theory is employed to estimate the crack driving force under the transient condition for an existing crack. Pores in materials are assumed to be saturated with moisture in the liquid form at the room temperature, which may vaporize as the temperature increases. The vaporization effects on the crack driving force are also studied. The ideal gas equation is employed to estimate the thermodynamic pressure due to vaporization at each time step after solving basic nodal values. A set of field equations governing the time dependent response of porous media are derived from balance laws based on the mixture theory. Darcy's law is assumed for the fluid flow through the porous media. Perzyna's viscoplastic model incorporating the Von-Mises yield criterion are implemented. The Green-Naghdi stress rate is used for the invariant of stress tensor under superposed rigid body motion. Isotropic elements are used for the spatial discretization and an iterative scheme based on the full Newton-Raphson method is used for solving the nonlinear governing equations.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1997년도 가을 학술발표회 논문집
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• pp.145-154
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• 1997

The results of optimum design by the deterministic approach adopted in the current design codes depend upon the safety levels of the applied code. But, it is now generally recognized that structural problems are nondeterministic and, consequently, that engineering optimum design must cope with uncertainties. Therefore, it is not an overstatement to affirm that the combination of reliability-based design procedures and optimization techniques is the only means of providing a powerful tool to obtain a practical optimum design solution. In the paper, reliability based optimum design procedure as a rational approach to optimum structural design is presented. The design constraints are formulated based on the ASD, LRFD and reliability theories. The reliability analysis is based on an advanced first-order second moment approach. Uncertainties in the structural strength and loading due to inherent variability as well as modeling and prediction errors are included in failure due to combined bending and shear. For the realistic reliability-based optimization of continuous steel box girder bridges, interactive non-linear limit state model is formulated based on the von Mises's combined stress yield criterion. Comparative results are presented when the ASD criteria are used for the optimum design of a structure under reliability constraints. In addition, this study comparatively shows the results of the optimum design for various criteria of design codes.

• 대한조선학회논문집
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• 제30권4호
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• pp.127-135
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• 1993

정확성과 단순성의 균형을 유지하면서 선박의 강도평가에 쉽게 적용할 수 있는 평판의 최종강도 간이추정식들을 도출하였다. 당 조선소의 건조선들 중 유조선과 산적화물선에 대한 선저부와 상갑판의 최종강도에 관련된 기하학적 변수들의 통계자료를 분석하여 구조특성을 살펴보고, 강도에 영향을 미치는 주요인수를 중심으로 하여 나머지 영향인자들을 확률분포에 따라 가중시켜 선종별로 평판의 최종강도 추정식을 제시하였다. 또한 저자들에[3-5] 의해 이미 제시된 새로운 좌굴평가식을 바탕으로 좌굴후거동에서 판의 중앙단부의 항복조건을 결부시켜 또하나의 최종강도 추정식을 제시하였다. 본 논문에서 제시한 간이식의 정확도를 실험식과 기존의 식[6, 7, 9]들과 비교 확인하였다.

• Structural Engineering and Mechanics
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• 제56권6호
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• pp.917-938
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• 2015

The nonlinear numerical analysis of the impact response of reinforced concrete/mortar beam incorporated with the updated Lagrangian method, namely the Smoothed Particle Hydrodynamics (SPH) is carried out in this study. The analysis includes the simulation of the effects of high mass low velocity impact load falling on beam structures. Three material models to describe the localized failure of structural elements are: (1) linear pressure-sensitive yield criteria (Drucker-Prager type) in the pre-peak regime for the concrete/mortar meanwhile, the shear strain energy criterion (Von Mises) is applied for the steel reinforcement (2) nonlinear hardening law by means of modified linear Drucker-Prager envelope by employing the plane cap surface to simulate the irreversible plastic behavior of concrete/mortar (3) implementation of linear and nonlinear softening in tension and compression regions, respectively, to express the complex behavior of concrete material during short time loading condition. Validation upon existing experimental test results is conducted, from which the impact behavior of concrete beams are best described using the SPH model adopting an average velocity and erosion algorithm, where instability in terms of numerical fragmentation is reduced considerably.

• Structural Engineering and Mechanics
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• 제8권3호
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• pp.233-242
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• 1999

In the present study, the elasto-plastic analysis of prismatic plate structures subjected to pure bending is carried out using the finite strip method. The end cross-sections of the structure are assumed to remain plane during deformation, and the compatibility along corner lines is ensured by choosing proper displacement functions. The effects of both the initial geometrical imperfections and residual stresses due to fabrication are included in the combined geometrically and materially nonlinear simulation. The von-Mises yield criterion and the Prandtl-Reuss flow theory of plasticity are applied in modelling the elasto-plastic behavior of material. Newton-Raphson iterations are carried out as the rotation of the end cross sections of the structure is increased step by step. The parameter representing the overall axial strain of structure is adjusted constantly during the iteration process in order to eliminate the resulting overall axial force on any cross-section of the structure in correspondence with the assumption of zero axial force in pure bending. Several numerical examples are presented to validate the present method and to investigate the effects of some material and geometrical parameters.

• Steel and Composite Structures
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• 제49권1호
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• pp.1-17
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• 2023

Based on Ahmadzadeh-Varvani hardening rule (A-V model), multiaxial ratcheting effect of Z2CND18.12N austenitic stainless steel is simulated by ABAQUS with user subroutine UMAT. The results show that the predicted results of the origin multiaxial A-V model are lower than the experimental data, and it is difficult to control ratcheting strain rate. In order to improve the predicted capability of A-V model, the A-V model is modified. In this study. Moreover, under the assumption of the von Mises yield criterion and normal plasticity flow rule, we develop a numerical algorithm of plastic strain with the improved model to implement the finite element calculation of the model. Internal iteration in the numerical algorithm was implemented with the Euler backward method, which calculated the trial strain for each equilibrium iteration using the consistent tangent matrix. With a user subroutine, the proposed model is programmed into ABAQUS for a user - executable version. By simulating the uniaxial ratcheting of a round bar made of Z2CND18.12N austenitic stainless steel, we observe that the predicted results simulated by ABAQUS with UMAT are compared with the experimental data. The predicted results of the improved multiaxial A-V model are consistent well with the experimental data.

• 한국안전학회지
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• 제11권4호
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• pp.143-150
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• 1996

본 연구는 선형, 비선형 hygrothermal 응력 문제를 위한 explicit-Implicit 유한요소 해석 모델 개발에 관한 것이다. 부가적으로 moilsture 확산 방정식, J-적분 평가를 위한 균열 요소 및 가상 균열 진전법이 도입된다. 시간 변화에 따른 균열 추진력을 계산하기 위하여 선형 탄성 파괴 역학(LEFM)이론이 고려되며 재료의 기공은 실온에서 액체 상태의 습기로 포화되어 있으며 온도가 상승함에 따라 증기화된다는 가정하에서 균열 추진력과 증기 효과의 관계가 연구된다. 이상 기체방정식은 각 시간 단계에서 증기에 의한 열역학적 압력을 계산하기 위하여 이용된다. 다공질 재료의 시간 종속 응답을 지배하는 방정식들은 혼합이론에 기초하며 다공질 재료의 유체 흐름을 위한 Darcy의 법칙과 Von-Mises 항복 기준을 포함하고 있는 Perzyna의 점소성 모델이 첨가된다. 또한 Green-Naghdi 응력률이 중첩된 강체 운동하에서 응력 텐서 invariant로 사용되며, 모델링을 위하여 사각요소가 이용되고 비선형 지배 방정식을 풀기 위하여 full Newton-Raphson법에 의한 반복법이 사용된다. 본 연구를 통하여 얻은 결과는 다음과 같다. 1) 본 유한요소 프로그램은 복합재의 hygrothermal 파괴 해석에 매우 유용하게 적용될 수 있다. 2) 습기의 온도에 의한 영향을 가지는 재료의 J-적분을 정확히 예측하기 위하여는 증기 효과를 고려하여야 한다. 왜냐하면 초기단계에 균열 전파력이 가속되기 때문이다. 3) 본 해석을 위해 Uncoupled scheme에 의한 결과도 Coupled scheme에 결과에 비해 아주 타당하므로 CPU 측면에서 매우 경제적인 Uncoupled scheme이 추천된다.