• Coupled systems mechanics
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• 제7권5호
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• pp.555-581
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• 2018

The moment-resistant steel frames are frequently used as a load-bearing structure of buildings. Global response of a moment-resistant frame structure strongly depends on connections behavior, which can significantly influence the response and load-bearing capacity of a steel frame structure. The analysis of a steel frame with included joints behavior is the main focus of this work. In particular, we analyze the behavior of two connection types through experimental tests, and we propose numerical beam model capable of representing connection behavior. The six experimental tests, under monotonic and cyclic loading, are performed for two different types of structural connections: end plate connection with an extended plate and end plate connection. The proposed damage-plasticity model of Reissner beam is able to capture both hardening and softening response under monotonic and cyclic loading. This model has 18 constitutive parameters, whose identification requires an elaborate procedure, which we illustrate in this work. We also present appropriate loading program and arrangement of measuring equipment, which is crucial for successful identification of constitutive parameters. Finally, throughout several practical examples, we illustrate that the steel structure connections are very important for correct prediction of the global steel frame structure response.

• 한국농공학회지
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• 제35권4호
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• pp.106-118
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• 1993

The purpose of this study is to develop a multireservoir water balance model which may be used to evaluate rural water demands such as agricultural water, domestic water, industrial water and livestock water and to determine effective storage of reservoir. The model was verified to compare the observed reservoir release data with the simulated reservoir release data of the existing Munsan and Dongbu reservoirs located in the Gisan rural district for 3 years('87~'89). For model application, the effective storages of existing reservoirs(Munsan & Dongbu) were evaluated for 10-year frequency drought and that of newly planned reservoirs(Kumbok & Kudong) were determined for 10-year frequency drought. In addition, the behavior of effective storages for existing reservoirs were analyzed in the case of introducing new reservoirs in the existing system.

• 한국지반공학회논문집
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• 제20권2호
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• pp.125-130
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• 2004

본 논문에서는 수치적 구성방정식인 연속 탄소성 캡 모델의 정수추정에 관한 방법이 제시되었다. 캡 모델을 이용하여 실제 토질의 거동을 예측하기 위하여서는 캡 모델을 이루는 토질의 물성과 직접적으로 연관된 여덟개의 정수가 결정되어야 한다. 이를 위하여 첫 번째로, Ottawa 모래를 사용하여 표준압밀시험기를 이용한 일축압축시험 및 배수삼축압측 시험이 토질거동의 실제기준값으로서 수행되었고, 두 번째로 탄소성 캡 수치해석모델의 반응을 실내실험값에 일치시키기 위하여 추정된 정수들을 사용한 수치실험이 수행되었다. 두 실험 간의 오차를 최소화하기 위하여 최적화 기법이 사용되었으며, 최적화 후 결정된 8개의 정수는 실내실험결과와 비교되었다. 특히, 수치적 삼축압축시험시 응력계산에 따른 수평변위 측정에 특별한 주의가 필요하다.

• Structural Engineering and Mechanics
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• 제33권4호
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• pp.391-406
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• 2009

Viscoelastic materials store as well as dissipate energy to the thermal domain under deformation. Two efficient modelling techniques reported in literature use coupled (thermo-mechanical) ATF (Augmenting Thermodynamic Fields) displacements and ADF (Anelastic Displacement Fields) displacements, to represent the constitutive relationship in time domain by using certain viscoelastic parameters. Viscoelastic parameters are first extracted from the storage modulus and loss factor normally reported in hand books with the help of Genetic Algorithm and then constitutive relationships are used to obtain the equations of motion of the continuum after discretizing it with finite beam elements. The equations of motion are solved to get the frequency response function and modal damping ratio. The process may be applied to study the dynamic behaviour of composite beams and rotors comprising of several viscoelastic layers. Dynamic behaviour of a composite beam, formed by concentric layers of steel and aluminium is studied as an example.

• Computers and Concrete
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• 제8권6호
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• pp.735-755
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• 2011

The capability of a multi-directional fixed smeared crack constitutive model to simulate the flexural/punching failure modes of fiber reinforced concrete (FRC) laminar structures is discussed. The constitutive model is implemented in a computer program based on the finite element method, where the FRC laminar structures were simulated according to the Reissner-Mindlin shell theory. The shell is discretized into layers for the simulation of the membrane, bending and out-of-plane shear nonlinear behavior. A stress-strain softening diagram is proposed to reproduce, after crack initiation, the evolution of the normal crack component. The in-plane shear crack component is obtained using the concept of shear retention factor, defined by a crack-strain dependent law. To capture the punching failure mode, a softening diagram is proposed to simulate the decrease of the out-of-plane shear stress components with the increase of the corresponding shear strain components, after crack initiation. With this relatively simple approach, accurate predictions of the behavior of FRC structures failing in bending and in shear can be obtained. To assess the predictive performance of the model, a punching experimental test of a module of a façade panel fabricated with steel fiber reinforced self-compacting concrete is numerically simulated. The influence of some parameters defining the softening diagrams is discussed.

• 한국지반신소재학회논문집
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• 제12권3호
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• pp.55-64
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• 2013

본 연구는 포천석분을 재성형하여 등방압축-팽창시험과 구속압력을 달리한 일련의 비배수삼축압축시험을 실시하여 Lade 단일항복면 구성모델의 토질매개변수를 결정하였으며, 실험결과의 역해석을 통하여 단일항복면 구성모델의 적용성과 포천석분의 거동특성을 확인하였다. 그 결과 포천석분은 축변형률이 증가함에 따라 축차응력이 증가하는 경화현상을 보이고 있으며 큰축변형률에서 파괴되므로 실용적인 파괴기준을 검토할 필요성을 확인하였으며, 구성모델의 11개 토질매개변수를 이용하여 시험치를 역해석한 결과 응력-변형거동을 양호하게 예측하지만 항복함수에 관련된 토질매개변수를 파괴규준에 관련한 상관식과 상수로 역해석한 경우는 다소 상이한 양상을 보이고 있다.

• Structural Engineering and Mechanics
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• 제14권4호
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• pp.435-454
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• 2002

The paper proposes analytical forms able to represent with very good approximation the constitutive law experimentally deducible by means of uniaxial cyclic compressive tests on material having softening post-peak behaviour in compression and negligible tensile strength. The envelope, unloading and reloading curves characterizing the proposed model adequately approach structural responses corresponding to different levels of nonlinearity and ductility, requiring a not very high number of parameters to be calibrated experimentally. The reliability of the model is shown by comparing the results that it is able to provide with the ones analytically deduced from two reference models (one for concrete, another for masonry) available in the literature, and with experimental results obtained by the authors in the framework of a research in progress.

• 한국분말재료학회지
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• 제11권4호
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• pp.301-307
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• 2004

Successful implementation of the powder forming process requires a detailed understanding of several interacting phenomena. The aim is to better control the process variables and to optimize the design parameters. A number of studies were carried out using various constitutive models that take the density change during powder forming into account. Most of them were developed for powders and sintered porous metals, but few of them can describe powder agglomerates, whose behaviour is different from that of uniformly arranged powders. The modification is needed to account for the effect of agglomeration on densification behaviour. Incorporating powder agglomeration into a constitutive model is of considerable importance, as it provides a possibility of relating the powder densification response to microstructural characteristics of powder particles, especially in case of nano powders. In this paper, we proposed a new powder agglomerate model in order to describe the unique densification behaviour of nano powders. The proposed model was applied to the densification of powder agglomerates during cold isostatic pressing.

• 한국산학기술학회논문지
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• 제10권1호
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• pp.171-176
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• 2009

본 논문에서는 표준 탄성-소성-점성 관계식에 근거하고, 수식을 간략화하기 위한 몇 가지 가정을 도입하여 전단속도에 능동적으로 대처할 수 있는 비교적 간단한 구성모델을 개발하였다. 개발된 모델은 정규압밀점토의 음력경로를 비교적 성공적으로 묘사하였다. 개발된 모델에서는 하나의 전단속도에서 결정한 모델변수 값들을 다른 전단속도 경우에도 적용할 수 있다는 장점이 있다. 모델변수 및 모델의 추가 간략화는 연속된 논문에서 설명된다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.668-673
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• 2008

In this paper, we developed a physically-based micromechanical model for inelastic deformation of ceramic powders. The aggregate response of ceramic particles was modeled using the two-surface yield function which considered the shear-induced dilatancy caused by friction, rolling resistance and cohesion between powder particles and consolidation caused by plastic deformation of powder themselves under high compression. The constitutive equations were implemented into the user-subroutine VUMAT of finite element program ABAQUS/Explicit. The material parameters in the constitutive model were identified by calibrating the model to reproduce data from triaxial compression tests and simple compression tests. The density distribution obtained by using the proposed model was in good quantitative agreement with the experimental results of the triaxial compression and cold isostaic compression as well.