• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.6
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• pp.130-137
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• 2018

Many constitutive models for concrete have been developed to predict the nonlinear behavior of concrete members considerably. The constitutive model for reinforcing bar that include the tension stiffening effect due to the bond characteristics between steel bars and concrete is being studied but the bilinear model is generally used. It was found that the buckling of the longitudinal reinforcing bars is controlled the nonlinear behavior of hybrid precast concrete panel, which is being developed for core wall. In this study, the constitutive models that can consider the embedding and buckling effects of reinforcing bar are investigated and a new model combing these constitutive models is proposed. In order to verify the proposed model, the analysis results are compared with experimental results of the concrete wall and hybrid precast concrete panel. The analysis of embedding-effect-only modeling predicted that the deformation increases continually without the decrease in the load carrying capacity. However, the analysis results of proposed model showed good agreement with some experimental results, thus verifying the proposed computational model.

• Journal of Korean Society of Steel Construction
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• v.18 no.2
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• pp.225-237
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• 2006

Based on the study conducted by Kim et al. (205a, b), an improved stability design method for evaluating the effective buckling lengths of beam-column members is proposed herein, using system elastic/inelastic buckling analysis and second-order elastic analysis. For this purpose, the stress-strain relationship of a column is inversely formulated from the reference load-carrying capacity proposed in design codes, so as to derive the tangent modulus of a column as a function of the slenderness ratio. The tangent stiffness matrix of a beam-column element is formulated using the so-called "stability functions," and elastic/inelastic buckling analysis Effective buckling lengths are then evaluated by extending the basic concept of a single simply-supported column to the individual members as one component of a whole frame structure. Through numerical examples of several structural systems and loading conditions, the possibilities of enhancement in stability design for frame structures are addressed by comparing their numerical results obtained when the present design method is used with those obtained when conventional stability design methods are used.

• Composites Research
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• v.34 no.2
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• pp.101-107
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• 2021

Composite structures have components and joints. Theses connections or joints can be potentially weak points in the structure. The failure mode of the composite bolted joint is designed as a bearing failure mode for structural safety. The load-displacement relation exhibits bearing failure mode shows a nonlinear behavior after the initial failure and progressive failure behavior. In order to accurately predict the failure behavior of composite bolted joints, this study modified the shear damage variable calculation process in the existing progressive failure analysis model. The results of the bearing stress-bearing strain of the composite bolted joint were predicted using the modified progressive failure analysis model, and the modified model was verified through comparison with the previous progressive analysis model.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.3
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• pp.919-930
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• 2014

In this study, the load capacities and behaviors of a shotcrete member with steel supports, as composite member, are investigated numerically by using a fiber section element. The cross section of a shotcrete lining with steel support is divided into a bundle of fibers, which are allocated nonlinear stress-strain relations and used for determining internal forces. To verify the used approach of the finite element method for shotcrete with steel supports, the load-displacement relations of shotcrete lining obtained by numerical analysis are compared with existing experimental results and are analyzed with the stress distribution of the shotcrete and steel support obtained numerically. As a result, it is shown that the proposed approach can predict the load capacities of each material and the overall nonlinear behavior of shotcrete lining with steel supports. The change of location of the neutral axis and the flexural resistance ratio of each material are also derived from the stress distribution of the cross section of the shotcrete lining with steel supports. From the results, it is concluded that the flexural resistance performance of steel support should be considered in shotcrete lining design.

• Journal of the Korea Concrete Institute
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• v.28 no.5
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• pp.535-544
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• 2016

This paper aims at examining the effects of sustained load and elevated temperature on the time-dependent deformation of a carbon fiber reinforced polymer (CFRP) sheets bonded to concrete as well as the pull-off strength of single-lap shear specimens after the sustained loading period using digital images. Elevated temperature during the sustained loading period resulted in increased slip of the CFRP composites, whereas increased curing time of the polymer resin prior to the sustained loading period resulted in reduced slip. Pull-off tests conducted after sustained loading period showed that the presence of sustained load resulted in increased pull-off strength and interfacial fracture energy. This beneficial effect decreased with increased creep duration. Based on analysis of digital images, results on strain distributions and fracture surfaces indicated that stress relaxation of the epoxy occurred in the 30 mm closest to the loaded end of the CFRP composites during sustained loading, which increased the pull-off strength provided the failure locus remained mostly in the concrete. For longer sustained loading duration, the failure mode of concrete-CFRP bond region can change from a cohesive failure in the concrete to an interfacial failure along the concrete/epoxy interface, which diminished part of the strength increase due to the stress relaxation of the adhesive.

• Tribology and Lubricants
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• v.28 no.1
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• pp.19-26
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• 2012

Rolling contact fatigue of an urban railway wheel was analysed during its rolling. A FEM analysis was performed using a 3D modelling of rail and wheel, considering the slope of the rail and nonlinear isotropic and kinematic hardening behavior of the rail and the wheel. The maximum von-Mises stress and contact pressure between the rail and wheel were 656.9 MPa and 1111.4 MPa, respectively, under axial load of 85 kN with friction coefficient of 0. The fatigue initiation life prediction relationships by strain-lifetime (${\varepsilon}$-N) and Smith-Watson-Topper method were drawn for the wheel steel as follows: $N_i=7.35{\times}10^6{\times}SWT^{-3.56}$ and $N_i=5.41{\times}10^{-9}{\times}(\frac{{\Delta}{\varepsilon}}{2})^{-5.77}$. The fatigue lifetimes of the wheel due to rolling contact were determined to be infinite by ${\varepsilon}$-N and SWT methods.

• Journal of Industrial Technology
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• v.20 no.A
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• pp.101-111
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• 2000

This research is results of experimental and numerical works on characteristic of strength increase and bearing capacity in dredged and reclaimed soil due to desiccation shrinkage. For a soil sampled from southern coastal area in Korea, basic soil property tests and standard consolidation test with falling head permeability tests were carried out to obtain consolidational characteristics of soil. Double cone penetration test, laboratory vane test and unconfined compression test were also performed to investigate the change of shear strength with degree of desiccation. Model tests were performed in 1G environment and 30G level artificially accelerated condition by using the centrifuge model test facilities to investigate the bearing capacity of desiccated ground. Test results were analyzed by using the theoretical and load-settlement characteristics method proposed by Meyehof & Hanna(1978). On the other hands, the numerical technique, using the finite strain consolidation theory considering the effect of desiccation was used to estimate the appropriate time of using heavy construction equipments in field with respect to strength increase due to desiccation.

• Transactions of Materials Processing
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• v.7 no.3
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• pp.260-273
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• 1998

A new blank design method is proposed to predict the optimum initial blank shape in the sheet metal forming process. The rollback method for blank shape design takes the difference between final deformed shaped and target contour shape into account. Based on the method a computer program composed of blank design module FE-analysis program and mesh generation module is developed. The rollback method is applied to square cup drawing process with the flange of unifiorm size around its periphery to confirm its validity. The optimum initial blank shape is obtained from an arbitrary square blank after three modification. Good agreements are recognized between the numerical results and the published results for initial blank shape and thickness strain distribution. The optimum blank shape for two parts of automobile sub-frame is designed, The thickness distribution and the level of punch load is improved. Also the method is applied to design the weld line in the tailor-welded blank. It is concluded that the rollback method is an effective and convenient method for an optimum blank shape design.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.09a
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• pp.467-472
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• 2010

Individual vacuum pressure method is soft ground improvement technique, in which a vacuum pressure can be directly applied to the vertical drain board to promote consolidation and strengthening the soft ground. This method does not require a surcharge load, different to embankment or pre-loading method. In this study, given the inner displacement of the ground where the individual vacuum pressure is applied, this dissertation aimed to reproduce the state of stress in the ground that is subject to the constraints created by the depth of improvement area. Modified Cam Clay theory which made it possible to take into account the isotropic displacement of the ground was applied to the NAP-IVP used simulation; the conception of equivalent permeability proposed by Hird was also applied so that the 3-dimensional real construction effect of drain materials could be reflected in the analysis.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.8
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• pp.740-746
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• 2008

In this paper, robust structural design of the PEMFC stack gasket is pursued with Taguchi method by considering the noise factor in stack assembly. The study of noise problem in stacking is required to secure the safety and performance improvement of PEMFC stack. The design parameters in the Taguchi method are selected so that the structural responses are insensitive to the noise factors. In the gasket analysis, a Mooney-Rivlin strain energy function is used to consider hyperelasticity between load and displacement. By uni-axial and equi-biaxial tension tests of the gasket, the material properties are determined for the use in robust design of PEMFC gasket. The robust design of the PEMFC stack may provide structural reliability.