• Proceedings of the Computational Structural Engineering Institute Conference
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• 2010.04a
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• pp.613-616
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• 2010

본 논문에서는 라인파이프 강관의 압축-휨 좌굴 성능 평가 기법을 개발하기 위해 비선형 유한요소해석을 사용하였다. 고강도 강재의 연성거동을 모사하기 위해 범용 유한요소해석 프로그램인 ABAQUS의 사용자 재료모델을 사용하여 GTN(Gurson-Tvergaad-Needleman) 모델을 작성하였다. 실험결과와의 비교를 통해 재료모델상수를 결정하였으며 압축-휨 좌굴 실험의 모사에 사용하였다. 압축-휨 좌굴 성능 평가는 비선형 유한요소해석의 결과로부터 얻어진 한계압축변형률과 최대휨모멘트를 기준으로 수행될 수 있다. 개발된 성능 평가 기법은 고강도 강재를 이용한 라인파이프의 설계 시 대변형 거동 분석에 유용하게 사용될 수 있다.

• Journal of Korean Society of Steel Construction
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• v.22 no.1
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• pp.1-12
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• 2010

According to the capacity design concept which forms the basis of the current steel seismic codes, the braces in concentrically braced frames (CBFs) should dissipate seismic energy through cyclic tension yielding and cyclic compression buckling while the beams and the columns should remain elastic. Brace buckling in inverted V-braced frames induces unbalanced vertical forces which, in turn, impose the additional beam moments and column axial forces. However, due to difficulty in predicting the location of buckling stories, the most conservative approach implied in the design code is to estimate the column axial forces by adding all the unbalanced vertical forces in the upper stories. One alternative approach, less conservative and recommended by the current code, is to estimate the column axial forces based on the amplified seismic load expected at the mechanism-level response. Both are either too conservative or lacking technical foundation. In this paper, three combination rules for a rational estimation of the column axial forces were proposed. The idea central to the three methods is to detect the stories of high buckling potential based on pushover analysis and dynamic behavior. The unbalanced vertical forces in the stories detected as high buckling potential are summed in a linear manner while those in other stories are combined by following the SRSS(square root of sum of squares) rule. The accuracy and design advantage of the three methods were validated by comparing extensive inelastic dynamic analysis results. The mode-shape based method(MSBM), which is both simple and accurate, is recommended as the method of choice for practicing engineers among the three.

• 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.

• 한국방재학회:학술대회논문집
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• 2011.02a
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• pp.40-40
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• 2011

현재 일반적으로 활용되고 있는 원통형 쉘구조로 이루어진 타워구조의 대형화가 추진되면서 제작, 운반 편의성, 단면효율성, 경제성 제고를 위해 다각형단면 기둥구조물의 활용이 대두되고 있다. 하지만 다각형 단면 기둥구조의 극한강도에 대한 자료가 충분치 않고 관련 기준이나 지침이 명확히 제시되고 있지 않은 실정이다. 본 연구에서는 원통형 쉘구조물을 다각형구조물로 대체하여 제작될 경우 축방향 압축에 대한 내하력 향상 효과를 수치해석적으로 검토해 보고자 한다. 해석모델은 지름 2m, 두께 20mm인 원형강관 프로토타입 풍력타워 구조를 참고로 하여 이에 내접하도록 결정한 6~12각형 단면 형상으로써 높이 10,000mm인 3차원 기둥모델을 구현하였고 유한요소프로그램인 ABAQUS를 이용하여 해석하였다. 각 subpanel의 중앙에 종방향 보강재를 설치하였을 때 국부좌굴에 대한 내하력 변화를 비교하기 위해 종방향보강재로 보강한 모델을 구성하여 비교 해석을 수행하였다. 종방향 보강재의 제원은 미국 SSRC 제안식을 기준으로 삼았다. 탄성좌굴해석을 통해 탄성좌굴모드 형상을, 비선형비탄성해석을 통해 최종파괴모드 및 극한강도를 얻었다. 보강 전 후의 탄성좌굴 해석 결과로부터 최소모드의 고유치 값을 비교하였다. 각 subpanel 단면 중심부에 한 개의 보강재를 설치한 경우 탄성좌굴강도가 4배 가량 증가하였다. 이로부터, 보강재(n=1) 설치에 따라 유효 폭두께비가 1/2로 감소하는 효과를 확인 할 수 있다. 비선형해석결과로부터 subpanel의 단면중심에 보강재를 설치한 경우 보강재가 위치한 곳에 고정점이 형성되어 이를 중심으로 국부 좌굴모드에 변화가 생기는 것이 확인되었다. 이러한 변화는 다각형 단면 기둥구조의 내하력 성능, 즉 국부좌굴강도에 영향을 준다. 충분한 강성을 갖는 종방향 보강재가 설치된 경우, 극한상태에서도 유효폭두께비가 줄어드는 것과 같은 강도 향상 효과를 확인할 수 있다. 이러한 사실은 각 해석결과 극한강도를 DIN code, Migita와 Fukumoto의 제안식, SSRC 설계제안식 등과의 비교를 통해 확인할 수 있었다.

• Proceedings of KOSOMES biannual meeting
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• 2005.05a
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• pp.179-183
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• 2005

The High-tensile steel has been recognized as a promising concept for structural design of light weight transportation systems such as aircraft high speed trains and fast ships. Using the high-tensile steel has been widely used in ship structures, and this enables to reduce the plate thickness. Using the high-tensile steel effectively for a ship hull, the plate thickness becomes thin so that plate buckling may take place. Therefore, precise assessment of the behavior of plate above primary buckling load is important. In this study, examined closely secondary buckling behavior after initial buckling of thin plate structure which operated compressive load according to the various kinds of yield stress with simply supported boundary condition. Analysis method is F.E.M by commercial program(ANSYS V7.1) and complicated nonlinear behaviour can analyze using art-length method about secondary buckling.

• Journal of the Korean GEO-environmental Society
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• v.7 no.6
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• pp.75-88
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• 2006

This paper evaluates the feasibility of use of high-strength steel for soil-metal corrugated steel structures. Two specifications, the AASHTO(2004) and the CHBDC(2000), were compared and the scientific background of equations for the buckling stability in those specifications were investigated to figure out the governing factors for buckling strength of structures. Numerous finite element analyses for round-pipe type of soil-metal corrugated steel structures were carried out with considering the elastic-plastic relationship of a material and the geometrical non-linearity, as well as the various design variables, such as span length, depths of soil cover, section properties, tensile strength and backfill conditions. Buckling strength equation of the CHBDC(2000) is still valid and conservative for both normal and high-strength steel soil-metal corrugated steel structures, and the buckling strength increases with the use of hight-strengths steel.

• Journal of Korean Society of Steel Construction
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• v.17 no.4 s.77
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• pp.439-447
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• 2005

When arch ribs are subjected to vertical loading, they may buckle suddenly towards the in-plane direction. Therefore, the designer should consider their in-plane stability. In this paper, the in-plane elastic and inelastic buckling strength of parabolic, fixed arch ribs subjected to vertical distributed loading were investigated using the finite element method. A finite element model for the snap-through and inelastic behavior of arch ribs was verified using other researchers' test results. The ultimate strength of arch ribs was determined by taking into account their large deformation, material inelasticity, and residual stress. Finally, the finite element analysis results were compared with the EC3 design code.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.4
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• pp.15-25
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• 1993

In order to promote the efficient use of composite materials, effort is currently being directed at the development of design criteria for composite structures. Insofar as design against buckling is concerned, it is well known that, for metal shells, a key step is the definition of 'knockdown' factors on the elastic critical buckling stress accounting mainly for the influence of initial geometric imperfections. At present, the imperfection sensitivity of composite shells has not been explored in detail. Due to the large number of parameters influencing buckling response (considerably larger than for isotropic shells), a very large number of tests would be needed to quantify imperfection sensitivity experimentally. An alternative approach is to use validated numerical models for this task. Thus, the objective of this paper is to outline the underlying theory used in developing a composite shell element and to present results from a validation exercise and subsequently from a parametric study on axially loaded glass fibre-reinforced plastic (GFRP) curved panels using finite element modelling. Both eigenvalue and incremental analyses are performed, the latter including the effect of initial geometric imperfection shape and amplitude, and the results are used to estimate 'knockdown' factors for such panels.

• 한국방재학회:학술대회논문집
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• 2010.02a
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• pp.84.1-84.1
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• 2010

국내에서는 플레이트거더의 휨 강도 및 전단 강도를 허용응력설계법에 기반한 도로교설계기준(2005)에 근거하여 규정하고 있으며, 국외의 경우 하중저항계수설계법에 근간을 둔 AISC(2005) 등의 규정을 통해 산정하고 있다. 최근에는 인장강도 800MPa 급의 강재가 생산되고 있으나 국내 설계기준에서는 아직까지 상기 인장강도를 갖는 고강도강에 대한 설계기준은 마련되지 않고 있다. 본 연구에서는 휨과 전단이 동시에 작용하는 고강도강 적용 플레이트거더의 극한거동 해석을 통해 국내기준의 적용성을 판단하고, 국외기준인 AISC(2005)와 비교하여 나타내어 허용응력설계법에 근거한 국내기준의 강도산정법의 한계점에 대해 고찰하였다.

• Journal of Korean Society of Steel Construction
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• v.23 no.6
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• pp.679-690
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• 2011

Since the elastic buckling problem of the plate has been studied both experimentally and theoretically, the buckling loads with various boundary conditions and loads can be easily determined. Currently, flange and web design specifications are based on the buckling stress and the post-buckling strength and include a safety-factor. Therefore, this study extended suchresearch to the linear buckling theory with ideal conditions and to the ultimate state with post-buckling. The current specifications are based on elastic buckling stress; and therefore, further research on the ultimate behavior of the plate is required. The ultimate strength design concept, which allows finite deflection, is used in this studyto maximize the post-buckling strength in a steel box. An empirical equation, which provides the ultimate strength of the steel box due to the change in the slenderness and optimum rigidity, are suggested based on the experiment results. Moreover, the appropriateness of the current design specifications was analyzed and discussed.