• Structural Engineering and Mechanics
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• v.70 no.1
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• pp.13-31
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• 2019

A nonlinear finite element model (FEM) using ATENA-3D software to simulate the axially compressive behavior of circular steel tube confined concrete (CSTCC) columns infilled with ultra high performance concrete (UHPC) was presented in this paper. Some modifications to the material type "CC3DNonlinCementitious2User" of UHPC without and with the incorporation of steel fibers (UHPFRC) in compression and tension were adopted in FEM. The predictions of utimate strength and axial load versus axial strain curves obtained from FEM were in a good agreement with the test results of eighteen tested columns. Based on the results of FEM, the load distribution on the steel tube and the concrete core was derived for each modeled column. Furthermore, the effect of bonding between the steel tube and the concrete core was clarified by the change of friction coefficient in the material type "CC3DInterface" in FEM. The numerical results revealed that the increase in the friction coefficient leads to a greater contribution from the steel tube, a decrease in the ultimate load and an increase in the magnitude of the loss of load capacity. By comparing the results of FEM with experimental results, the appropriate friction coefficient between the steel tube and the concrete core was defined as 0.3 to 0.6. In addition to the numerical evaluation, eighteen analytical models for confined concrete in the literature were used to predict the peak confined strength to assess their suitability. To cope with CSTCC stub and intermediate columns, the equations for estimating the lateral confining stress and the equations for considering the slenderness in the selected models were proposed. It was found that all selected models except for EC2 (2004) gave a very good prediction. Among them, the model of Bing et al. (2001) was the best predictor.

• Computers and Concrete
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• v.20 no.3
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• pp.319-327
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• 2017

Studying the structural behavior of prestressed segmented girders is quite important due to the large use this type of solution in viaducts and bridges. Thus, this work presents a nonlinear three-dimensional structural analysis of an externally prestressed segmented concrete girder through the Finite Element Method (FEM), using a customized ANSYS platform, version 14.5. Aiming the minimization of the computational effort by using the lowest number of finite elements, a new viscoelastoplastic material model has been implemented for the structural concrete with the UPF customization tool of ANSYS, adding new subroutines, written in FORTRAN programming language, to the main program. This model takes into consideration the cracking of concrete in its formulation, being based on fib Model Code 2010, which uses Ottosen rupture surface as the rupture criterion. By implementing this new material model, it was possible to use the three-dimensional 20-node quadratic element SOLID186 to model the concrete. Upon validation of the model, an externally prestressed segmented box concrete girder that was originally lab tested by Aparicio et al. (2002) has been computationally simulated. In the discretization of the structure, in addition to element SOLID186 for the concrete, unidimensional element LINK180 has been used to model the prestressing tendons, as well as contact elements CONTA174 and TARGE170 to simulate the dry joints along the segmented girder. Stresses in the concrete and in the prestressing tendons are assessed, as well as joint openings and load versus deflection diagrams. A comparison between numerical and experimental data is also presented, showing a good agreement.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.4
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• pp.657-663
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• 2018

In this study, shape optimization was performed to improve the vibration isolation capability of an anti-vibration rubber assembly, which is used in the field option cabin of agricultural tractors. A uniaxial tension test and biaxial tension test were performed to characterize the hyper-elastic material properties of rubber, and the data were used to calibrate the material model used in the finite element analyses. A field test was performed to quantify the input excitation from the tractor and the output response at the cabin frame. To account for the nonlinear behavior of rubber, static analyses were performed and the load-displacement curve of rubber was derived. The stiffness of the rubber was calculated from this curve and input to the harmonic analyses of the cabin. The results were verified using the test data. Taguchi's parameter design method was used to find the optimal shape of the anti-vibration rubber assembly, which indicated a shape with reduced stiffness. The vibration of the cabin frame was reduced by the optimization by as much as 35% compared to the initial design.

• Journal of the Korean Society for Railway
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• v.11 no.3
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• pp.257-262
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• 2008

Design and analysis of road subgrade system, which is exposed to repetitive loading condition, uses resilient modulus. The behavior of railway subgrade system will not be quite different from that of road system. Following this phenomenological feature of the subgrade system, this paper introduces the implementation of the resilient modulus based constitutive model on a commercial finite element software. The implementation of the resilient modulus models such as K-${\theta}$ and Uzan on a FE program has been conducted previously. These model assumes that the material state reaches to the nonlinear elastic condition and with further application of repetitive loads, the response of material is completed in elastic condition. According to the recent test results performed on cohesive subgrade soils, however, permanent deformation occurs with repetitive loads. With aids of previously suggested models the permanent deformation cannot be modeled. To overcome such limitation a plastic potential derived from the test results and simple failure criterion based constitutive model is developed. The comparison between the analysis and test results shows a good correlation.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.1
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• pp.29-38
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• 1994

Linear composite theory as well as a finite element program is developed for axisymmetric elastomeric bearings. This study is limited to axisymmetrically loaded horizontal layered systems with linear, elastic, small' deformation conditions. A multiscale method is used in the development of the composite theory which enables us to model inhomogeneous layered composites as equivalent homogeneous, orthotropic material. Only continuity of the prime variables is required for the finite element analysis, allowing the use of simple $C_o$ elements whereas rather complicated theories presented in the past need more requirements. Four node isoparametric elements are used in the study. The developed theory of this paper is limited to linear conditions, however, the analysis can be extended to nonlinear behavior of flexible material in elastomeric bearing by using multiscale method presented here. Two numerical examples are examined and compared to the results of discrete and previously obtained composite analysis to verify the theory.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.11
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• pp.1297-1303
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• 2012

In this paper, the standard procedures for measuring the moisture sorption properties of thin polymeric materials such as polyethylene terephthalate (PET) by using the thermo-gravimetric method to characterize the moisture diffusion in the polymer are presented, and the sorption properties are quantified. The moisture diffusivity and solubility are characterized to investigate the effect of temperature and humidity on the moisture sorption properties according to the Arrhenius equation. The validation of the obtained sorption properties using thermogravimetry is discussed with the measured permeability based on Fickian diffusion. The nonlinear behavior of the concentration dependent moisture diffusion is investigated experimentally, and the nonlinearity is characterized numerically for the case of having an interface with an inorganic material such as a metal. The Fickian/Non-Fickian model based on the obtained moisture sorption properties is compared and discussed.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.1
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• pp.21-28
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• 2008

Stress-strain curves based on Ramberg-Osgood and Hollomon relations are strongly dependent upon the regressed range of strain. This work investigates mathematical expressions of true stress-strain curves of metallic materials. We first observe the variation of yield strength, strain hardening exponent and stress-strain curve with regressed range of stain. Based on sectional regression and expression using one or two parameters, we propose an optimal strain range for which yield strength and nonlinear material behavior are quite appropriate.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.21 no.8
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• pp.738-748
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• 2008

In this study, it has been investigated on the changing behavior of electrical properties in $ZnO-Bi_2O_3-Sb_2O_3$ (Sb/Bi=2.0, 1.0 and 0.5) ceramics. The samples were prepared by conventional ceramic process, and then characterized by I-V, C-V curve plots, impedance and modulus spectroscopy (IS & MS) measurement. The electrical properties of ZBS systems were strongly dependent on Sb/Bi. In ZBS systems, the varistor characteristics were deteriorated noticeably with increasing Sb/Bi and the donor density and interface state density were increased with increasing Sb/Bi. On the other hand, we observed that the grain boundary reacted actively with the ambient oxygen according to Sb/Bi ratio. Especially the grain boundaries of Sb/Bi=0.5 systems were divided into two types, i.e. sensitive to oxygen and thus electrically active one and electrically inactive intergranular one with temperature. Besides, the increased pyrochlore and $\beta$-spinel phase with Sb/Bi ratio caused the distributional inhomogeneity in the grain boundary barrier height and the temperature instability. To the contrary, the grain boundary layer was relatively homogeneous and more stable to temperature change and kept the system highly nonlinear at high Bi-rich phase contents.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.5
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• pp.121-128
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• 2012

In this paper, nonlinear analysis for reinforced concrete structure for power transmission line is performed by considering the characteristics of the failure, which are depend on loading conditions and concrete material models. On the numerical evaluation for the failure behavior, the finite element analysis is applied. For the concrete material model, microplane model based on concrete damage is introduced. However, to describe the crack bridging effect of long and short fiber of steel fiber reinforced concrete (SFRC), tensile softening model is suggested and applied for SFRC. An numerical results by finite element technique are compared with the experiment results for box culvert specimen. Comparing on the experimental and analytical results, validity and reliability of numerical analysis are investigated.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.6A
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• pp.577-585
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• 2009

A 9-node degenerated shell finite element(FE), which has been developed for assessment of ultimate pressure capacity and nonlinear analysis for nuclear containment building is described in this paper. Reissner-Midnlin(RM) assumptions are adopted to develop the shell FE so that transverse shear deformation effects is considered. Material model for concrete prior to cracking is constructed based on the equivalent stress-equivalent strain relationship. Tension stiffening model, shear transfer mechanism and compressive strength reduction model are used to model the material behavior of concrete after cracking. Niwa and Aoyagi-Yamada failure criteria have been adapted to find initial cracking point in compression-tension and tension-tension region, respectively. Finally, the performance of the developed program is tested and demonstrated with several examples. From the numerical tests, the present results show a good agreement with experimental data or other numerical results.