Stiffness Requirement for Flat-Bar Longitudinal Stiffener of Box-Girder Compression Flanges

Do Dai Thang,구민세,정영도,Asif Hameed 한국강구조학회 2009 International Journal of Steel Structures Vol.9 No.2

In this paper, the moment of inertia requirement of flat-bar longitudinal stiffener of bottom flange in steel box girder is investigated through finite element modeling. The required minimum stiffness for longitudinal stiffeners of box girder flange is given in the AASHTO LRFD Bridge Design Specification and is modified by Yoo. However, this requirement is adopted for T-shape stiffeners. Here, the effect of important parameters on the minimum required moment of inertia of flat-bar stiffener is numerically investigated by examining the anti-symmetric mode of buckling. This study presents the results that are based on 3D finite-element analysis of four hundred hypothetical compression flange models stiffened by varying numbers of flatbar longitudinal stiffeners with realistic dimensions such as the height of stiffener, the thickness of the compression flange, the number of longitudinal stiffeners and the aspect ratio of plate panel. A new proposed equation for required minimum stiffness of the flat-bar longitudinal stiffeners is derived from nonlinear regression analyses. Beside that the study has taken into account the effect of boundary conditions and the effect of inelastic transition on the critical buckling stress of compression flange. Through the evaluation of a design example, the validity and reliability of the new proposed equation is demonstrated. In this paper, the moment of inertia requirement of flat-bar longitudinal stiffener of bottom flange in steel box girder is investigated through finite element modeling. The required minimum stiffness for longitudinal stiffeners of box girder flange is given in the AASHTO LRFD Bridge Design Specification and is modified by Yoo. However, this requirement is adopted for T-shape stiffeners. Here, the effect of important parameters on the minimum required moment of inertia of flat-bar stiffener is numerically investigated by examining the anti-symmetric mode of buckling. This study presents the results that are based on 3D finite-element analysis of four hundred hypothetical compression flange models stiffened by varying numbers of flatbar longitudinal stiffeners with realistic dimensions such as the height of stiffener, the thickness of the compression flange, the number of longitudinal stiffeners and the aspect ratio of plate panel. A new proposed equation for required minimum stiffness of the flat-bar longitudinal stiffeners is derived from nonlinear regression analyses. Beside that the study has taken into account the effect of boundary conditions and the effect of inelastic transition on the critical buckling stress of compression flange. Through the evaluation of a design example, the validity and reliability of the new proposed equation is demonstrated.

이중합성 강박스거더에서 전단연결재에 의해 보강된 압축플랜지의 극한거동에 관한 연구

이두성(Lee Doo Sung),이성철(Lee Sung Chul),서석구(Suh Suk Koo) 대한토목학회 2008 대한토목학회논문집 A Vol.28 No.4A

종방향 보강재는 압축플랜지를 단순지지함으로써 국부좌굴강도를 증가시키는 역할을 수행한다. 최근 연구에 의하면, 종방향으로 적절한 간격을 두고 점지지 되었을 경우 그 선을 따라서 단순 지지된 경우와 동일한 좌굴강도를 보이는 것으로 밝혀졌다. 이 같은 연구결과로부터, 하부콘크리트에 부착된 전단연결재가 압축플랜지의 좌굴시 점지지 조건을 만족할 수 있다면 전단연결재가 단순지지의 역할도 수행할 수 있을 것이라는 예측이 가능하다. 이와 같은 사실이 입증이 된다면, 강박스거더 제작비에서 매우 큰 부분을 차지하는 종방향보강재를 생략할 수 있기 때문에 보다 경제적인 설계가 기능해 질 것이다. 본 연구에서는 하부압축플랜지에 종방향보강재를 대체할 전단연결재의 종방향 배치 시 최소간격 결정과 동시에 하부 콘크리트와 합성거동을 하기 위해 소요되는 전단연결재 소요 개수와 간격을 결정하기 위한 연구를 수행하였다. The longitudinal stiffener performs its role to increase the local buckling strength by making simple support upon compression flange. In the recent researches, it is investigated that compression flange with point supports on certain arrangement reveals the same strength with longitudinal stiffeners. From this results, it is predictable that shear stud could perform the role of longitudinal stiffener if shear stud embedded in concrete satisfies the requirement to point-support under yield stress of the compression flange. In this study, the researches were performed to investigate the optimally required arrangement space of longitudinal point-support for which the shear stud replacing the longitudinal stiffeners and simultaneously determine the required numbers and space of shear stud for completely composite behavior between compression bottom flange and bottom concrete on the double composite girder system.

절곡강판을 적용한 강박스거더 압축플랜지의 탄성좌굴 및 극한 거동

김도형,이성철 한국강구조학회 2018 韓國鋼構造學會 論文集 Vol.30 No.4

강박스거더의 압축플랜지는 국부좌굴강도 증가를 위해 종방향 보강재가 설치된다. 종방향 보강재는 탄성좌굴이 발생할 때, 압축플랜지에 연속적인 지지조건을 제공하도록 설계된다. 보강재로 나누어진 서브 패널은 독립적으로 지지된 판으로 가정하며, 이때 서브패널의 경계조건은 보강재의 강성에 좌우된다. 본 연구에서는 압축플랜지에 종방향 보강재를 설치하는 대신 보강재 위치를 따라 종방향으로 판을 절곡하는 새로운 개념의 압축플랜지를 선형 좌굴해석 및 비선형 극한해석을 통해 검토하였다. 절곡을 통해 나누어진 서브패널은 적절한 각도 이상 절곡하는 경우 서로 단순지지조건을 제공한다. 본 연구에서 개발된 절곡 플랜지는 기존 보강 플랜지에 비해 경제적인 대안이 될 수 있을 것으로 판단된다. Wide compression flanges used in steel box girders are often stiffened with longitudinal stiffeners and sometimes in conjunction with transverse stiffeners, to increase local buckling strength. In a few design codes, longitudinal stiffeners are designed to provide continuous support during elastic buckling. The subpanels divided by the stiffeners are treated as independently supported plates, and the support condition depends on the rigidity of the stiffeners. This study introduces a new type of compression flange that is not stiffened with the longitudinal stiffeners and is instead folded longitudinally along the stiffener lines. The subpanels divided by folding provide simple support to each other if folded with a proper angle. The folded flange could be a cost-effective alternative to stiffened wide flanges.

Research on the tightening strategy of bolted flange for contact stiffness of joint surface

Weiliang Zuo,Zhifeng Liu,Yongsheng Zhao,Nana Niu,Mingpo Zheng 국제구조공학회 2022 Structural Engineering and Mechanics, An Int'l Jou Vol.83 No.3

During bolted flange assembly, the contact stiffness of some areas of the joint surface may be low due to the elastic interaction. In order to improve the contact stiffness at the lowest position of bolted flange, the correlation model between the initial bolt pre-tightening force and the contact stiffness of bolted flange is established in this paper. According to the stress distribution model of a single bolt, an assumption of uniform local contact stiffness of bolted flange is made. Moreover, the joint surface is divided into the compressive stress region and the elastic interaction region. Based on the fractal contact theory, the relationship model of contact stiffness and contact force of the joint surface is proposed. Considering the elastic interaction coefficient method, the correlation model of the initial bolt pre-tightening force and the contact stiffness of bolted flange is established. This model can be employed to reverse determine the tightening strategy of the bolt group according to working conditions. As a result, this provides a new idea for the digital design of tightening strategy of bolt group for contact stiffness of bolted flange. The tightening strategy of the bolted flange is optimized by using the correlation model of initial bolt pretightening force and the contact stiffness of bolted flange. After optimization, the average contact stiffness of the joint surface increased by 5%, and the minimum contact stiffness increased by 6%.

종방향 보강재를 갖는 곡선 압축플랜지의 전단좌굴계수에 관한 연구

이두성(Lee Doo Sung),박찬식(Park Chan Sik),이성철(Lee Sung Chul) 대한토목학회 2007 대한토목학회논문집 A Vol.27 No.3A

곡선교는 직선교와 달리 활하중뿐만 아니라 고정하중상태에서도 비틀림모멘트가 발생하여, St. Venant 전단흐름이 발생된다. 따라서 곡선박스거더 압축플랜지는 압축과 전단의 상호작용이 반드시 고려되어야 한다. 본 연구에서는 강곡선 박스거더 압축플랜지의 종방향보강재를 압축에 대해 단순지지역할을 하도록 Yoo et al. (2001)의 식으로 설계된 깅곡선 압축플랜지의 전단좌굴계수를 수치해석을 통해서 조사하였다. 본 연구는 유한요소해석 프로그램인 ADINA 8.1(ADINA R & D, Inc.)을 이용하여 매개변수해석을 수행하였다. 본 연구에서는 압축플랜지에서 전단좌굴계수를 형상비와 보강재 개수에 따른 식으로 간략화하기 위하여 수치해석결과에 대한 회귀분석을 통해 강곡선패널의 전단좌굴계수식이 유도되었으며, 기존의 복잡한 전단좌굴계수 산정식을 형상비와 보강재 수만의 간략화 된 전단좌굴계수 제안식은 해석결과와 유사한 결과를 보였다. Unlike straight girders, horizontally curved steel box girders are necessarily subjected to torsion and as a consequence, the Saint Venant torsional shear flow will develop in the flange and web plates. Therefore, the local buckling behavior of steel box girder flanges becomes complicated due to the combined action of compression and shear. In the present study, the elastic buckling behavior of longitudinally stiffened compression flanges of horizontally curved steel box girders is investigated through a 3D finite element analysis. The results are compared with the provisions in AASHTO Guide Specifications for Horizontally Curved Steel Girder Highway Bridges (2003). It was found that the finite element analysis results indicate that the equation for the determination of the shear buckling coefficient of longitudinally stiffened flanges is invalid or can be conservatively used for practical designs. From results of finite element analysis, it is proposed a simplified equation calculated by aspect ratio and the number of stiffener for shear buckling coefficient of compression flange with longitudinally rigid stiffeners that is designed by proposal equation of Yoo et al. (2001).

Folded Plate Theory에 의한 압축플랜지의 비선형 해석

정수형,심재수 한국구조물진단유지관리공학회 2008 한국구조물진단유지관리공학회 논문집 Vol.12 No.5

압축플랜지의 설계는 단순히 종방향 보강재와 횡방향 보강재로 둘러싸인 서브패널(sub-panel)의 극한거동에 대해 적절한 안전율을 도입하여 이루어져 왔다. 그러나, 종방향 보강재의 수와 강성, 횡방향 보강재의 간격, 초기 변형량과 잔류응력의 분포 등 제 영향을 고려해서 압축플랜지 전체의 극한강도를 결정하는 것이 합리적이다. 본 연구에서는 Folded Plate 이론에 근거하여 압축플랜지에 대해 기하강성의 영향, 재료적 비선형성을 고려한 해석 프로그램을 개발하고 이를 바탕으로 국내에서 실제 시공된 강박스거더교의 압축플랜지에 적용하였다. Compressive flanges of steel box girder is designed based on the ultimate strength behavior of sub-panel which is enclosed with longitudinal stiffeners and transverse stiffeners on appropriate safety factor. However, it is rational that the ultimate strength is calculated considering the various factors such as number and stiffness of longitudinal stiffener, spacing of transverse stiffener, initial deformation and residual stress distribution. In this study, an analysis program based on Folded Plate theory is developed considering the geometric effects and the material nonlinearity. The analysis program is applicated to the steel box girder bridges which is really constructed in domestic.