• Computational Structural Engineering
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• v.4 no.1
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• pp.73-82
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• 1991

Recently, the finite element method has been sucessfully extended to treat the rather complex phenomena such as nonlinear buckling problems which are of considerable practical interest. In this study, a finite element program to evaluate the elasto-plastic buckling stress is developed. The Stowell's deformation theory for the plastic buckling of flat plates, which is in good agreement with experimental results, is used to evaluate bending stiffness matrix. A bifurcation analysis is performed to compute the elasto-plastic buckling stress. The subspace iteration method is employed to find the eigenvalues. The results are compared with corresponding exact solutions to the governing equations presented by Stowell and also with experimental data due to Pride. The developed program is applied to obtain elastic and elasto-plastic buckling stresses for various loading cases. The effect of different plate aspect ratio is also investigated.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.1A
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• pp.53-60
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• 2009

This paper deals with the geometrical nonlinear analyses of post-buckled columns with variable cross-section. The objective columns having variable cross-section of the width, depth and square tapers are supported by both hinged ends. By using the Bernoulli-Euler beam theory, differential equations governing the elastica of post-buckled column and their boundary conditions are derived. The solution methods of these differential equations which have two unknown parameters are developed. As the numerical results, equilibrium paths, elasticas and stress resultants of the post-buckled columns are presented. Laboratory scaled experiments were conducted for validating the theories developed in this study.

• Journal of Korean Society of Steel Construction
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• v.21 no.5
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• pp.505-514
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• 2009

This paper describes the structural behavior and the ultimate strengths of circular hollow steel (CHS) sections based on a series of compression tests. The ultimate strengths of CHS section columns are mainly dependent on both diameter-thickness ratio and column slenderness ratio. For the CHS sections with a high diameter-thickness ratio, an elastic or an inelastic local buckling may occur prior to the overall buckling, and it may decrease the column strength. Test sections were fabricated from SM400 steel plate of 2.8 mm and 3.2 mm in thickness and were tested to failure. The diameter-thickness ratios of the test sections ranged from 45 to 170 to investigate the effect of local buckling on the column strength. The compression tests indicated that the CHS sections of lower diameter-thickness ratio than the yield limit in the current design specifications showed an inelastic local buckling and a significant post-buckling strength in the local mode. Their ultimate stresses were larger than the nominal yield stress. It was known that the allowable stresses of the sections predicted by the Korean Highway Bridge Design Specifications (2005) were too conservative in comparison with test results. The Direct Strength Method which was newly developed was calibrated for application to the CHS sections by the experimental and numerical results. The Direct Strength Method proposed can predict properly the ultimate strength of CHS section columns whether a local buckling and an overall buckling occur nearly simultaneously or not.

• 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.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.5
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• pp.952-958
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• 1988

To analyze the nonflatness and residual stress in accelerated cooled plate, a numerical analysis model has been developed. Two factors, i.e. temperature and phase transformation, are considered in calculating the stress distribution that develops during cooling. The plastic strain and plate-buckling, which are often shown in accelerated cooled plate, were determined from this stress. Mean temperature in through thickness direction and temperature difference in width direction are considered in the model to simplify the calculation. The temperature and stress distribution changes caused by phase transformation are involved in terms of the effective specific heat and the effective thermal expansion coefficient. With the model, accelerated cooling of 10mm(t) $^{*}$3000mm(w) plate was simulated. The condition of accelerated cooling was .deg. C/sec from just after hot rolling to 500.deg. C. The initial temperature-difference ratio, .DELTA.Tr, in width direction is an important factor in evaluating the stress distribution. When .DELTA.Tr is 0.08, buckling occurs during cooling and 7kgf/m $m^{2}$ of residual stress develops at the edge of plate. To secure the flatness, .DELTA.Tr should be less than 0.07. Small scaled cooling test was conducted to verify the exactness of the model and the results proved the usefulness of this numerical analysis model.l.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.2
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• pp.205-212
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• 1989

The minimum weight design for the simply supported orthogonally stiffened cylindrical shell subjected to axial compression is studied by a mathematical programming. A smeared-out method is used for the computation of buckling load in the optimization process and optimization is accomplished by a gradient projection method. Maximum eight design variables and twenty-one inequality constraints considering the buckling, stress and geometric restraints are used. The three stringer types are considered as the optimization models : (1) rectangular stringer (2) I-stringer (3) T-stringer. Two design examples are compared with those in the other studies and the results demonstrate the validity of the present study. From the calculation the design with T-stringer can be more efficient than the one with rectangular or I-stringer.

• Proceeding of EDISON Challenge
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• 2015.03a
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• pp.191-196
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• 2015

해상 pedestal 크레인은 각종 운송물을 선박에 싣거나 내리는 해상 운송에 필수적인 장비이다. 따라서 구조적 안전성을 가지는 크레인 설계가 요구된다. 그의 일환으로 수행된 '해상 pedestal 크레인의 설계 개선을 위한 연구'에서는 기존 크레인의 기초 설계에 대해서 구조적 안전성올 평가하여 개선 방안을 제시하였다. 또한 좌굴 안정성 향상을 위한 보강재 설계를 수행하였다. 하지만 상세설계 관점에서 미비한 점이 있어 이를 보완할 필요성이 있다. 안전성 평가를 위해 필요한 응력을 계산하기 위해 EDISON-CSD프로그램을 통해 유한요소모델 해석을 활용한 구조해석을 수행하였다. 효율적인 해석을 위해 상세설계에 필요한 부분영역을 선택하여 모델링 하였으며 전체영역에서의 해석 결과 값을 등가 힘, 등가 모멘트로 환산하여 경계조건으로 부여하였다. 보강재간의 교차점 형상이 안전성에 미치는 영향을 보기위해 stiffener와 diaphragm의 교차점 형상(반원, 정사각형, 사다리꼴)에 따라 안전성 평가를 수행하였고, 안전 여유의 유효한 차이를 보이지 않음을 확인하였다. 평가에 필요한 응력계산을 위해 또한 Diaphragm의 좌굴에 대한 영향을 고려하기 위해 설계 규격 DNV-RP-201 8장(Buckling of girders)을 분석하였고, 안전성 평가에 반영하였다. 또한 실제 현장에서 보편적으로 사용되는 angle 형상 stiffener의 치수 도출을 위해 최적설계를 수행하였고, 모든 설계 제한조건을 만족하면서 최소의 무게를 가지는 합리적인 치수를 도출하였다.

• Journal of the Korean Society of Hazard Mitigation
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• v.8 no.2
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• pp.45-49
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• 2008

This paper investigated the accuracy of the current design formulae for the elastic buckling strength of web-tapered I-beams in AISC-LRFD specification. The basic concept is to replace a tapered beam by an equivalent prismatic beam with a different length, but with a cross section identical to that of the smaller end of the tapered beam. The modification factor, B, is used to account for the stress gradient within the unbraced length and the lateral restraining effects offered by the adjacent segments. The modification factor(B) suggested in AISC-LRFD specification was compared with the finite element method(FEM) results. This paper presented a redefined method to calculate the modification factor(B).

• Computational Structural Engineering
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• v.10 no.4
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• pp.165-175
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• 1997

In this paper, the stress, buckling and vibration analyses have been performed for several case with the spot weld stiffened rear side frame, the unstiffened rear side frame and the dual thickness laser weld rear side frame. For stress and vibration analyses, the clamped boundary condition with spring supports are used. But for the buckling analyses, the both ends simply supported boundary conditions are used. For the nummerical analyses, ANSYS 5.0 code is adopted. Maximum stress of the spot weld stiffened rear side frame occurs in the main frame and is 80.9 MPa. Maximum strain is 501 .mu.. The maximum stress of the dual thickness laser weld rear side frame of 1.8mm thickness structure is equal with the stress of spot weld stiffened frame. The weight of dual thickness laser weld frame can be reduced about 17.2%. For the stiffened spot weld rear side frame with both ends simply supported boundary conditon, the bucking load is 52.54 kN. When the thickness of the dual thickness laser weld rear side frame become 1.9mm thickness structure, the buckling load of the stiffenerd rear side frame is equal to that of dual thickness laser weld frame. The reduction of the structure weight is about 5%. The fundamental natural frequency of the stiffened spot weld rear side frame for bending mode is 163.6 Hz and that of the dual thickness laser weld rear side frame is 179.8 Hz.

• Journal of Korean Society of Steel Construction
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• v.23 no.6
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• pp.647-657
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• 2011

This paper describes the moment capacity of flexural members with local buckling based on a series of FE and experiment results. Thin-walled flexural members undergo local, lateral-torsional, or interactive buckling according to the section geometries and lateral boundary conditions. Flexural members with large width-to-thickness ratios in the flanges or the web may undergo local buckling before lateral-torsional buckling. Local buckling has a negative effect on the flexural strength based on the lateral-torsional buckling of flexural members. This phenomenon should be considered in the estimation of the flexural strength of thin-walled sections. Flexural members with various width-to-thickness ratios in their flanges and web were analyzed. Initial imperfections in the local buckling mode, and residual stresses, were included in the FE analyses. Simple bending moment formulae for flexural members were proposed based on the FE and test results to account for local and lateral-torsional buckling. The proposed bending moment formulae for the thin-walled flexural members in the Direct Strength Method use the empirical strength formula and the grosssection modulus. The ultimate flexural strengths predicted by the proposed moment formulae were compared with the AISC (2005), Eurocode3 (2003), and Korean Highway Bridge Design Specifications (2010). The comparison showed that the proposed bending moment formulae can reasonably predict the ultimate moment capacity of thin-walled flexural members.