• Structural Engineering and Mechanics
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• v.61 no.5
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• pp.625-635
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• 2017

Sets of nonlinear formulations together with an energy-based damage index (DI) are proposed to model the behavior and quantify the damage of the confined and unconfined concretes under monotonic and cyclic loading. The proposed formulations and DI can be employed in numerical simulations to determine the stresses and the damages to the fibers or the layers within the sections of reinforced concrete (RC) components. To verify the proposed formulations, an adaptive finite element computer program was generated to simulate the RC structures subjected to monotonic and cyclic loading. By comparing the simulated and the experimental test results, on both the full-scale structural members and concrete cylindrical samples, the proposed uniaxial behavior modeling formulations for confined and unconfined concretes under monotonic and cyclic loading, based on an iterative process, were accordingly adjusted, and then validated. The proposed formulations have strong mathematical structures and can readily be adapted to achieve a higher degree of precision by improving the relevant coefficients based on more precise tests. To apply the proposed DI, the stress-strain data of concrete elements is required. It can easily be calculated by using the proposed nonlinear constitutive laws for confined and unconfined concretes in this paper.

• Journal of Magnetics
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• v.9 no.2
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• pp.60-64
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• 2004

In this paper calculations of magnetisation and magnetoresistance characteristics of the Spin Valve (SV) and Pseudo Spin Valve (PSV) spintronics structures are reported and compared with the experimental data. The magnetisation reversal process was analysed with respect to the Stoner- Wohlfahrt model of total surface energy in terms of uniaxial anisotropy, exchange coupling between ferromagnetic layers, unidirectional exchange anisotropy of pinned layer (modelled by exchange coupling between magnetisation of pinned layer and net magnetisation of antiferromagnetic layer with high anisotropy). The numerical simulation of the model to the experimental magnetisation data yielded the above parameters for SV and PSV structures. These parameters were used to more sophistically micromagnetic modelling tool originating from the project called Object Oriented Micromagnetic Framework. Influence of the shape anisotropy of the Magnetic Tunnelling Junction cell used in MRAM was simulated by means of micromagnetic simulations. Results were compared to those obtained from the spot Kerr measurements.

• Journal of the Korean Geotechnical Society
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• v.19 no.4
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• pp.75-81
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• 2003

To investigate the reinforcing effect of subsurface layers of marine dredged clay(DMC) mixed with the micro-fiber(MF), a series of laboratory tests were performed on the DMC specimens with and without MF through uniaxial and triaxial compression tests. For the test programme, the elapsed time after dredging of marine clay, mixing rate and length of MF, and curing time of the composite were chosen as the important factors affecting the strength behaviour. The strength of the DMC mixed with MF and waste lime(WL) used for the admixture was found to be enhanced with the increasing content and length of MF, and with decreasing water content of DMC. MF and WL were applied as materials for trafficability improvement of the very soft reclaimed ground by DMC.

• Structural Engineering and Mechanics
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• v.55 no.1
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• pp.47-64
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• 2015

This paper presents the effect of hybridization material on variation of critical buckling load with different cross-ply laminates plate resting on elastic foundations of Winkler and Pasternak types subjected to combine uniaxial and biaxial loading by using two variable refined plate theories. Governing equations are derived from the principle of virtual displacement; the formulation is based on a new trigonometric shape function of displacement taking into account transverse shear deformation effects vary parabolically across the thickness satisfying shear stress free surface conditions. These equations are solved analytically using the Navier solution of a simply supported. The influence of the various parameters geometric and material, the thickness ratio, and the number of layers symmetric and antisymmetric hybrid laminates material has been investigated to find the critical buckling loads. The numerical results obtained through the present study with several examples are presented to verify and compared with other models with the ones available in the literature.

• Korean Journal of Optics and Photonics
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• v.24 no.5
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• pp.271-278
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• 2013

The effective reflection coefficients of an obliquely incident wave on a multi-layered substrate coated with a uniaxially anisotropic alignment layer are derived. The effective reflection coefficients as well as explicit ellipsometric expressions are provided as a function of film constants of multiple layers together with magnitude of anisotropy, direction of optic axis, and thickness of the alignment layer. It is expected that by adapting these expressions to the conventional modelling technique, the ordinary refractive index, the extra-ordinary refractive index, the azimuth angle and the tilt angle of the optic axis, and the thickness of the aligned surface can be determined simultaneously together with the thickness and volume fraction of each layer beneath the alignment layer.

• Steel and Composite Structures
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• v.47 no.6
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• pp.759-779
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• 2023

The paper proposes two hybrid metaheuristic optimization and artificial neural network (ANN) methods for the close prediction of the ultimate axial compressive capacity of concentrically loaded concrete filled double skin steel tube (CFDST) columns. Two metaheuristic optimization, namely genetic algorithm (GA) and particle swarm optimization (PSO), approaches enable the dynamic training architecture underlying an ANN model by optimizing the number and sizes of hidden layers as well as the weights and biases of the neurons, simultaneously. The former is termed as GA-ANN, and the latter as PSO-ANN. These techniques utilize the gradient-based optimization with Bayesian regularization that enhances the optimization process. The proposed GA-ANN and PSO-ANN methods construct the predictive ANNs from 125 available experimental datasets and present the superior performance over standard ANNs. Both the hybrid GA-ANN and PSO-ANN methods are encoded within a user-friendly graphical interface that can reliably map out the accurate ultimate axial compressive capacity of CFDST columns with various geometry and material parameters.

• Journal of the Korean Geotechnical Society
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• v.29 no.12
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• pp.5-10
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• 2013

Bearing capacity of a drilled shaft can be separated into side resistance and base resistance. But in domestic design procedure side resistance is usually underestimated compared with base resistance. Results of bi-directional test showed that measured side resistances in each different layers are larger than those evaluated from several suggested methods. In this study, measured side resistances in each different layer of drilled shafts installed in domestic sites are analyzed and compared with evaluated side resistances from the method using revised SPT N value. For weathered rock and soft rock layer, from which rock core can hardly be obtained, we suggested new evaluated methods using revised SPT N value instead of the method using uniaxial compressive strength of rock. Resuts showed that the ranges of side resistance of cohesive and non-cohesive layer are $f_s{\leq}5tf/m^2$ and $f_s{\leq}15tf/m^2$ respectively. Range of side resistance in weathered rock is $15tf/m^2$ < $f_s{\leq}50tf/m^2$ and that in soft rock $f_s{\geq}35tf/m^2$.

• Journal of the Korean Society for Advanced Composite Structures
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• v.4 no.2
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• pp.39-44
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• 2013

This study is aimed to examine the influence of the rotational stiffness of U-shaped ribs on the local buckling behaviors of laminated composite plates. Applying the orthotropic plates with eight layers of the layup $[(0^{\circ})4]s$ and $[(0^{\circ}/90^{\circ})2]s$, 3-dimensional finite element models for the U-rib stiffened plates were setup by using ABAQUS and then a series of eigenvalue analyses were conducted. There is a need to develope a simple design equation to establish the rotational stiffness effect, which could be easily quantified by comparing the theoretical critical stress equation for laminated composite plates with elastic restraints based on the Classical laminated plate theory. Through the parametric numerical studies, it is confirmed that there should clearly exist an increasing effect of local plate buckling strength due to the rotational stiffness by closed-section ribs. An applicable coefficient for practical design should be verified and proposed for future study. This study will contribute to the future study for establishing an increasing coefficient for the design strength and optimum design of U-rib stiffened plates.

• International Journal of Highway Engineering
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• v.17 no.2
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• pp.39-46
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• 2015

PURPOSES: The objectives of this study were to develop a new polymer-modified emulsion for application to tack coats and to evaluate its properties by comparing it with other types of asphalt emulsions, with the goal of providing an enhanced tack coat material for use in construction. METHODS: Modified asphalt binders were developed from using SBS and SBR latex in the laboratory, and their fundamental properties, such as their penetration index and PG grade, were evaluated. Based on the properties, a new tack coat material was developed. To evaluate the newly developed asphalt emulsion, the bonding strength between the two layers of HMA was measured by applying a uniaxial tensile test and shear test. For the tests, a total of four different conditions were applied to the specimens, including the developed asphalt emulsion, latex modified asphalt emulsion, conventional asphalt emulsion, and non-tack coating. RESULTS AND CONCLUSIONS: Overall, the developed asphalt emulsion exhibits the best bonding strength behavior among all of the three types. Also, the two types of polymer-modified emulsions were found to be better for application for use as a tack coat than a conventional emulsion. Especially, at a high temperature ($50^{\circ}C$), the conventional asphalt emulsion no longer acts as a tack coating material. Therefore, the polymer-modified emulsion should be considered for application to tack coat construction during the summer.

• Magazine of the Korea Concrete Institute
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• v.7 no.1
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• pp.145-155
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• 1995

The purpose of this paper is to present an analysis method which can exactly analyze load-deflection relationships. crack propagations and stresses and strains of steel reinforccnlent and concrete in hehaviors of elastic, mclastic and ultlmate ranges of reinforced concretc beams under monotonically increasing loads. For these purposes, the material nonlinearities are taken into account by comprising the tension. compression and shear models of cracked concrete and a model for reinforcement in the concrete. Smeared crack model is used as a modeling of concrete. The steel reinforcement is assumed to be in an uniaxial stress state and modeled srncaretl layers of eqivalent thickness and line elernents for correct positiori arid behavior. For the verification of application and validity of the method proposed in this paper, several numerical examples are analyzed and compared with those from other researchers. As a results, this method shown in 3.5-15(%) error is correct.