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Flexural-torsional buckling of stepped beams subjected to pure bending

  • Structural Engineering
  • Published:
KSCE Journal of Civil Engineering Aims and scope

Abstract

The cross sections of continuous multi-span beams are sometimes increased suddenly, or stepped, at interior supports of continuous beams to resist high negative moments. An investigation of the elastic flexural-torsional buckling (FTB) behavior of I-shaped stepped beams was conducted using finite element method (FEM) and resulted in the development of design equations for beams having singly or doubly stepped cross sections within a laterally unbraced length. The finite element models are subjected to pure bending moment in the entire beam span. Results from the design equations were demonstrated with comparisons between the proposed equations or the weighted average approach (WAA) and FEM results for doubly and singly stepped beam spans of existing highway bridges. The new equations proposed definitely improve current design methods for the FTB problem and increase efficiency in building and bridge design. The proposed solutions can be easily used to develop new design equation for FTB resistance of stepped beams subjected to general loading condition such as a concentrated load, a series of concentrated loads or uniformly distributed load.

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Abbreviations

C b :

modifier for moment gradient

C st :

stepped beam factor based on action of pure bending

C w :

warping constant of beam

E :

modulus of elasticity of steel

G :

shear modulus of elasticity of steel

h :

beam depth

I y :

moment of inertia of beam aboutY-axis

J :

St. Venant torsional constant for beam

L b :

laterally unbraced length

M 0 :

end moment that produce largest compressive stress on bottom flange

M 1 :

smaller end moment of beam

M CL :

moment at centerline of segment

M ocr :

flexural-torsional buckling strength of prismatic beam under pure bending

M ost :

flexural-torsional buckling strength of stepped beam under pure bending

α:

ratio of stepped length along span

β:

ratio for defining relative flange width of large and small cross section; and

γ:

ratio for defining relative flange thickness of large and small cross section

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Authors and Affiliations

  1. Department of Civil Engineering, 238 Harbert Engineering Center, Auburn University, 36849, AL, USA

    Jong Sup Park (Member, Research Fellow)

  2. Department of Civil and Environmental Engineering, Korea University, Seoul, Korea

    Young-Jong Kang (Member, Professor)

Authors
  1. Jong Sup Park
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  2. Young-Jong Kang
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Correspondence to Jong Sup Park.

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Park, J.S., Kang, YJ. Flexural-torsional buckling of stepped beams subjected to pure bending. KSCE J Civ Eng 8, 75–82 (2004). https://doi.org/10.1007/BF02829083

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  • DOI: https://doi.org/10.1007/BF02829083

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