• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.4
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• pp.703-710
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• 1994

A nonlinear FEM analysis of steel members under very-low-cycle loading has been performed in conjunction with experimental works. This analysis is an FEM tracing toward cracking of steel members under cyclic loads such as a strong earthquake. After verifying the procedure by comparing global hysteretic behaviors from the analytical and experimental results, the local stress-strain hysteresis at critical sections for large cyclic deformations was traced by the numerical analysis. Local strain history was discussed in relation to cracking. Based on the experimental and analytical results, a new approach to seismic safety assessment for steel members was proposed in this paper.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.7 s.262
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• pp.792-799
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• 2007

A newly developed cellular metal based on kagome lattice is an ideal candidate for multifunctional materials achieving various optimal properties. Intensive efforts have been devoted to develop efficient techniques for mass production due to its wide potential applications. Since a variety of imperfections would be inevitably included in the realistic fabrication processes, it is highly important to examine the correlation between the imperfections and material strengths. Previous performance tests were mostly done by numerical simulations such as finite element method (FEM), but only for perfect structures without any imperfection. In this paper, we developed an efficient numerical framework using nonlinear random network analysis (RNA) to verify how the statistical imperfections (geometrical and material property) contribute to the performance of general truss structures. The numerical results for kagome truss structures are compared with experimental measurements on 3-layerd WBK (wire-woven bulk kagome). The mechanical strength of the kagome structures is shown relatively stable with the Gaussian types of imperfections.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.09a
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• pp.201-204
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• 2010

Earthquake load to design a structure has been calculated from a fixed base SDOF model using amplified surface accelerations along soft soil layers. But the method dose not consider a soil-structure interaction. Centrifugal experiments that were consisted of soil, a shallow foundation and a structure were performed to find the effects of soil-structure interaction. The experiments showed that mass and stiffness of the foundation affected a response of the structure and nonlinear behavior of soil near the foundation. And a rocking displacement caused by overturning moment affected the response and increases a damping effect. In this study, the centrifugal experiment was simulated as a two dimensional finite element model. The finite element model was used for nonlinear time domain analysis of the OpenSees program. The numerical model accurately evaluated the behaviors of soil and the foundation, but the rocking effect and the behavior of structure were not described.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.78-83
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• 2007

A newly developed cellular metal based on kagome lattice is an ideal candidate for multifunctional materials achieving various optimal properties. Intensive efforts have been devoted to develop efficient techniques for mass production due to its wide potential applications. Since a variety of imperfections would be inevitably included in the realistic fabrication processes, it is highly important to examine the correlation between the imperfections and material strengths. Previous performance tests were mostly done by numerical simulations such as finite element method (FEM), but only for perfect structures without any imperfection. In this paper, we developed an efficient numerical framework using nonlinear random network analysis (RNA) to verify how the statistical imperfections (geometrical and material property) contribute to the performance of general truss structures. The numerical results for kagome truss structures are compared with experimental measurements on 3-layerd WBK (wire-woven bulk kagome). The mechanical strength of the kagome structures is shown relatively stable with the Gaussian types of imperfections.

• Journal of Environmental Impact Assessment
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• v.16 no.1
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• pp.79-87
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• 2007

The performance of a stream water quality analysis model depends upon many factors attributed to the geological characteristics of a watershed as well as the distribution behaviors of pollutant itself on a surface of watershed. Because the model run has to import the pollution load from the watershed as a boundary condition along an interface between a stream water body and a watershed, it has been used to introduce a pollution delivery coefficient to behalf of the boundary condition of load importation. Although a nonlinear regression model (NRM) was developed to cope with the limitation of a conventional empirical way, this an up-to-date study has also a limitation that it can't be applied where the pollution load washed off (assumed at a source) is less than that delivered (observed) in a stream. The objective of this study is to identify what causes the limitation of NRM and to suggest how we can purify the process to evaluate a pollution delivery coefficient using many field observed cases. As a major result, it was found what causes the pollution load delivered to becomes bigger than that assumed at the source. In addition, the pollution load discharged to a stream water body from a specific watershed was calculated more accurately.

• Journal of Biosystems Engineering
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• v.18 no.3
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• pp.262-269
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• 1993

Stress relaxation behaviors of the cucumber under bending moment were tested with UTM at three levels of loading rate and initial deflection ratio. Sample cucumber was selected from three cultivars of cucumber, Cheongjangmadi, Baekdadagi, and Gyeousalicheongjang, because these cultivars are the most popular grown cultivars in Korea. When the bending moment was applied to the cucumber sample, the effective span between simple supports was held a constant value of 116mm with consideration of the selected sample length. The objectives of this study were to develop the rheological models such as linear and nonlinear models of the stress relaxation for the cucumber samples, and to investigate the effects of loading rate and initial deflection ratio on the stress relaxation behavior of the cucumber. The results of this study may be summarized as follows : 1. Stress relaxation behavior of the cucumber could be well described by the generalized Maxwell model for each level of deflection ratio. But the stress relaxation behavior of the sample was found to be initial deflection ratio and time dependent, and it was represented the nonlinear viscoelastic model as a function of initial deflection ratio and time. 2. Stress relaxation behavior of the cucumber samples was very highly affected by the loading rate and the initial deflection ratio. The more loading rate and initial deflection ratio resulted in the more initial bending stress and after stress relaxation progressed more rapidly. 3. At the same test conditions, it was found that the stress relaxation rate of Cheongjangmadi was faster than that of other cultivars.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.12
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• pp.6521-6526
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• 2013

Elastic and nonlinear ultimate strength analyses were conducted to examine the effects of the stiffness and slenderness of flat-type stiffeners on ultimate in-plane strengths of a stiffened plate system. Although it is not feasible to consider local buckling in the stiffeners in elastic analysis, it was confirmed that the in-plane strengths of the stiffened plate system can be achieved by antisymmetric buckling mode when a certain level of stiffness in the stiffeners is provided. Nonlinear ultimate strength analysis, in which initial imperfection and residual stress are incorporated, showed that the ultimate strengths are sensitively affected by the mode shapes for initial imperfections. The slenderness limit for flat-type stiffeners in KHBDC (Korean Highway Bridge Design Code) was evaluated as conservative compared to the analysis results.

• Journal of the Earthquake Engineering Society of Korea
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• v.15 no.5
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• pp.45-54
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• 2011

This paper presents a nonlinear finite element analysis procedure for the performance assessment of deteriorated reinforced concrete bridge columns. A computer program, named RCAHEST (Reinforced Concrete Analysis in Higher Evaluation System Technology), was used to analyze these reinforced concrete structures. Material nonlinearity is taken into account by comprising tensile, compressive and shear models of cracked concrete and a model of reinforcing steel. Advanced deteriorated material models are developed to predict behaviors of deteriorated reinforced concrete bridge columns. The proposed numerical method for the performance of damaged reinforced concrete bridge columns is verified by comparison with reliable experimental results.

• Journal of the Earthquake Engineering Society of Korea
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• v.22 no.7
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• pp.379-390
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• 2018

In this study, a numerical approach based on mid-point integrated finite elements and a viscous boundary is proposed for time-domain wave-propagation analyses in infinite poroelastic media. The proposed approach is accurate, efficient, and easy to implement in time-domain analyses. In the approach, an infinite domain is truncated at some distance. The truncated domain is represented by mid-point integrated finite elements with real element-lengths and a viscous boundary is attached to the end of the domain. Given that the dynamic behaviors of the proposed model can be expressed in terms of mass, damping, and stiffness matrices only, it can be implemented easily in the displacement-based finite-element formulation. No convolutional operations are required for time-domain calculations because the coefficient matrices are constant. The proposed numerical approach is applied to typical wave-propagation and soil-structure interaction problems. The model is verified to produce accurate and stable results. It is demonstrated that the numerical approach can be applied successfully to nonlinear soil-structure interaction problems.

• Steel and Composite Structures
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• v.27 no.3
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• pp.255-271
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• 2018

This paper deals with the transient dynamic analysis and elastic wave propagation in a functionally graded graphene platelets (FGGPLs)-reinforced composite thick hollow cylinder, which is subjected to shock loading. A micromechanical model based on the Halpin-Tsai model and rule of mixture is modified for nonlinear functionally graded distributions of graphene platelets (GPLs) in polymer matrix of composites. The governing equations are derived for an axisymmetric FGGPLs-reinforced composite cylinder with a finite length and then solved using a hybrid meshless method based on the generalized finite difference (GFD) and Newmark finite difference methods. A numerical time discretization is performed for the dynamic problem using the Newmark method. The dynamic behaviors of the displacements and stresses are obtained and discussed in detail using the modified micromechanical model and meshless GFD method. The effects of the reinforcement of the composite cylinder by GPLs on the elastic wave propagations in both displacement and stress fields are obtained for various parameters. It is concluded that the proposed micromechanical model and also the meshless GFD method have a high capability to simulate the composite structures under shock loadings, which are reinforced by FGGPLs. It is shown that the modified micromechanical model and solution technique based on the meshless GFD method are accurate. Also, the time histories of the field variables are shown for various parameters.