KSCE Journal of Civil Engineering

, Volume 8, Issue 1, pp 75–82 | Cite as

Flexural-torsional buckling of stepped beams subjected to pure bending

Structural Engineering
Received:
Accepted:

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.

Keywords

lateral stability stability analysis buckling beams 

Notation The following symbols are used in this paper

Cb

modifier for moment gradient

Cst

stepped beam factor based on action of pure bending

Cw

warping constant of beam

E

modulus of elasticity of steel

G

shear modulus of elasticity of steel

h

beam depth

Iy

moment of inertia of beam aboutY-axis

J

St. Venant torsional constant for beam

Lb

laterally unbraced length

M0

end moment that produce largest compressive stress on bottom flange

M1

smaller end moment of beam

MCL

moment at centerline of segment

Mocr

flexural-torsional buckling strength of prismatic beam under pure bending

Most

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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Copyright information

© KSCE and Springer jointly 2004

Authors and Affiliations

  1. 1.Department of Civil Engineering, 238 Harbert Engineering CenterAuburn UniversityUSA
  2. 2.Department of Civil and Environmental EngineeringKorea UniversitySeoulKorea

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