• Structural Engineering and Mechanics
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• 제53권1호
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• pp.147-158
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• 2015

Elements used in steel structures may be considered as an assembly of number of thin flat walls. Local buckling of these members can limit the buckling capacity of axial load resistance or flexural strength. We can avoid a premature failure, caused by effects of local buckling, by limiting the value of the wall slenderness which depend on its critical buckling stress. According to Eurocode 3, the buckling stress is calculated for an internal wall assuming that the latter is a simply supported plate on its contour. This assumption considers, without further requirement, that the two orthogonal walls to this wall are sufficiently rigid to constitute fixed supports to it. In this paper, we focus on webs of steel profiles that are internal walls delimited by flanges profiles. The objective is to determine, for a given web, flanges dimensions from which the latter can be considered as simple support for this web.

• Steel and Composite Structures
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• 제43권2호
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• pp.271-278
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• 2022

Buckling is one of the most critical phoneme in the design of steel structures. Lateral torsional buckling (LTB) is particularly significant for slender beams generally subjected to loading in plane. The web distortion effects on LTB are not addressed explicitly in standards for flexural design of steel I-section members. Hence, the present study is focused to predict the influence of the web distortion on the elastic (L_r) limiting lengths given in American Institute of Steel Construction (AISC) code for the lateral torsional buckling (LTB) behavior of steel beams due to no provision in the code for consideration of web distortion. For this aim, the W44x335 beam is adopted in the buckling analysis carried out by the ABAQUS finite element (FE) program since it is one of the most critical sections in terms of lateral torsional buckling (LTB). The strain results at mid-height of the web at mid-span of the beam are taken into account as the monitoring parameters. The web strain results are found to be relatively greater than the yield strain value when L/L_r is equal to 1.0. In other words, the ratio of L/L_r is estimated from the numerical analysis to be about 1.5 when the beam reaches its first yielding at mid-span of the beam at mid-height of the section. Due to the effect of web distortion, the elastic limiting length (L_r) from the numerical analysis is obtained to be considered as greater than the calculated length from the code formulation. It is suggested that the formulations of the limiting length proposed in the code can be corrected considering the influence of the web distortion. This correction can be a modification factor or a shape factor that reduces sectional slenderness for the LTB formulation in the code.

• Advances in Computational Design
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• 제6권1호
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• pp.55-75
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• 2021

The lightweight superstructure is beneficial for bridges in remote areas and emergency erection. In such weight-sensitive applications, the combination of fiber-reinforced polymer (FRP) as a material and box-beams as a structural system have enormous scope. This combination offers various advantages, but as a thin-walled structure, their designs are often governed by buckling criteria. FRP box-beams lose their stability either by flange or web buckling mode. In this paper, the web buckling behavior of simply supported FRP box-beam subjected to transverse load has been studied by modeling full box-beam to consider the effect of real state of stress (stress variation in length direction) and boundary conditions (rotational restraint at web-flange junction). A parametric study by varying the sectional geometry and fiber orientation is carried out by using ANSYS software. The accuracy of the FE models was ensured by verifying them against the available results provided in the literature. With the help of developed database the influential parameters (i.e., αs, βw, δw and γ) affecting the web bucklings are identified. Design trends have been developed which will be helpful to the designers in the preliminary stage. Finally, the importance of governing parameters and design trends are demonstrated through pedestrian bridge design.

• 한국공간구조학회논문집
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• 제7권3호
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• pp.119-124
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• 2007

장스팬 철골부재설계시, 응력보다는 처짐에 의해 부재단면이 결정되며 이러한 경우 춤을 극대화 할 수 있는 셀룰러 빔이 매우 유리하다. 셀룰러 빔은 웨브의 단면결손으로 인해 웨브의 좌굴강도가 일반형강보의 비해 작아지게 된다. 본 논문에서는 셀룰러 빔의 개구부간격과 직경비, 그리고 개구부직경과 웨브두께비를 주요변수로 비선형 유한요소해석을 통해 웨브포트의 좌굴강도를 평가하였다. 또한 이를 BS5950 Part 1에서 제시하고 있는 기준과 비교분석하였다.

• 대한토목학회논문집
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• 제28권3A호
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• pp.367-373
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• 2008

국내/외에서 설계되는 강곡선거더교 복부판의 전단강도는 복부판의 4변을 단순지지라는 가정 하에서 산정되는 탄성전단좌굴강도로 제안하고 있다(AASHTO Guide Specifications, 2003). 그러나, Lee et al.(1996, 1999)과 Bradford(1996)의 최근 연구에서 실제의 설계범위를 갖는 직선이나 곡선 복부판에서 어느 정도의 강성을 갖는 플랜지에 의해서 접하는 변의 경계조건은 단순지지 보다는 고정지지에 더 근접하며, 복부판의 형상비에 따라서는 AASHTO의 탄성좌굴강도가 60%이상 낮게 평가되고 있음을 발표하였다. 특히 강곡선복부판의 전단좌굴강도는 곡률의 영향으로 AASHTO Guide Specifications(2003)의 탄성전단좌굴강도보다 최대 38%이상 증가하고 있음이 Lee and Yoo(1999)의 연구에서 조사되었다. 본 논문에서는 선형좌굴해석을 이용하여 곡률과 경계조건이 동시에 고려된 강곡선 복부판의 전단좌굴계수를 합리적으로 추정할 수 있는 산정식을 제안하고자 한다.

• Journal of Mechanical Science and Technology
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• 제16권10호
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• pp.1211-1221
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• 2002

A shape optimization of stiffener was conducted to increase buckling load or failure load with stiffened laminated composite panel of I-type under compression loading. Design variables are cap length, web length, and/or thickness under the constraint of volume constancy. The objective function is buckling load and failure load of post-buckling based on Tsai-Hill theory using ABAQUS 5.8 for analysis and Optimizer on Broydon-Fletcher Goldfarb-Sharno Method and Augmented Lagrange Multiplier Method. The effects of relative length of a web and a cap of stiffener on buckling load and failure load of post-buckling were investigated with the results of optimum design.

• 한국강구조학회 논문집
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• 제23권4호
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• pp.455-464
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• 2011

본 논문에서는 곡선 보강 복부판의 좌굴해석을 대체전단변형률 장을 갖는 8, 9절점 평면 쉘요소를 이용한 유한요소해석을 통하여 수행하였다. 수평보강재 및 수직보강재를 갖는 경우의 수직면내 곡선 복부판의 좌굴거동을 조사하기 위해 면내 모멘트 하중을 받는 경우에 대해서 복부판의 폭(b)의 변화, 보강재와 복부판의 휨-강성비(${\gamma}=EI/bD$)의 변화에 대한 변수연구를 수행하였다. 보강재를 갖지 않는 경우의 수직면내 곡선 복부판의 정적거동에 대해서도 조사되었다. 또한 모멘트 하중을 받는 경우에서 수평 보강재 및 수직 보강재의 좌굴능력이 비교 되었다.

• Steel and Composite Structures
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• 제22권6호
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• pp.1465-1486
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• 2016

Conventional plate I-girders are sensitive to local buckling of the web when they are subjected mainly to shear action because the slenderness of the web in out-of-plane direction is much bigger. The local buckling of the web can also cause the distorsion of the plate flange under compression as a thin-walled plate has very low torsional stiffness due to its open section. A new I-girder consisted of corrugated web, a concrete-filled rectangular tubular flange under compression and a plate flange under tension is presented to improve its resistance to local buckling of the web and distorsion of the flat plate flange under compression. Experimental tests on a conventional plate I-girder and a new presented I-girder are conducted to study the failure process and the failure mechanisms of the two specimens. Strain developments at some critical positions, load-lateral displacement curves, and load-deflection curves of the two specimens have all be measured and analyzed. Based on these results, the failure mechanisms of the two kinds of I-girders are discussed.

• 한국강구조학회 논문집
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• 제9권1호통권30호
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• pp.37-49
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• 1997

The buckling behavior of the web of steel girders are largely dependent on the size and the location of stiffeners and the restraining effect of top and bottom flanges. Elastic and inelastic buckling analyses based or the Spline Finite Strip Method were executed to study the stiffening effect of the longitudinal stiffener on the web of box girders and to find how the top and bottom flanges had effects on the web, where geometric boundary conditions were limited by both hinged, both fixed and the flange sections. The basic assumption for the longitudinal end boundary conditions was that the vertical stiffeners had the rigidity enough to force nil deflection line on the web panel so that the junction line between web and vertical stiffener was assumed to be hinged boundary conditions. The provisions on the longitudinal stiffener of the plate and box girders of the Korean Standard Highway Bridge Specifications(1995) and AASHTO Specifications(1994 LRFD) were compared with the results obtained numerically for the various longitudinal stiffener size of box girders. Simple equations and design curves for the longitudinal stiffener of the web were proposed for the practical use.

• 한국강구조학회 논문집
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• 제23권2호
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• pp.221-228
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• 2011

강 판형교는 높은 세장비 때문에 좌굴이 설계의 주요 변수이다. 본 연구의 목적은 I 형 플레이트 거더와 파형 복부판을 갖는 플레이트 거더의 좌굴거동을 분석하고, 파형 복부판을 갖는 플레이트 거더의 이점을 조사하는 것이다. 파형 복부판 깊이의 변화, 복부판의 두께 변화 그리고 하중조건의 변화에 따라 다양한 파라미터 연구를 수행하였다. 연구의 결과로서 파형 복부판을 갖는 플레이트 거더의 좌굴강도가 I 형 플레이트 거더에 비해서 좌굴강도에 있어서 46%~417% 더 효과적이며, 파형 복부판을 갖는 플레이트 거더의 적절한 파형각도는 ${\theta}=15^{\circ}{\sim}22^{\circ}$로 나타났다.