doi:10.3850/978-981-08-6218-3_SS-Th036 Final Paper PDF

A COMPARISON OF INTERNATIONAL DESIGN STANDARDS FOR ASSESSING LATERAL STABILITY OF STEEL BEAMS

A. Surovek1,a, I. Macphedran2, V. Palaniswamy1,b and M. Bradford3

1 Civil and Environmental Eng., South Dakota School of Mines and Tech., Rapid City, SD.
asurovek@sdsmt.edu
bvarunaraaja.palaniswamy@mines.sdsmt.edu
2 I.T.S., University of Saskatchewan, Saskatoon, SK.
Ian.MacPhedran@usask.ca
3 Centre for Infrastructure Engineering and Safety, The University of New South Wales, Sydney, NSW. m.bradford@unsw.edu.au

EXTENDED ABSTRACT

Structural engineering is increasingly a global commodity service. As engineers are required more often to develop designs in international locations, it becomes necessary for them to understand the basic philosophies and methodologies of the numerous international structural design codes and standards. This paper compares the basic design approaches for assessing the lateral stability and strength of steel beams of many major international structural steel design standards including

The beams considered are doubly-symmetric “I” shaped sections, whose section strength is not limited by local buckling effects. There are a number of common features that these standards share: they all use a limit states design philosophy, with load and resistance factors; the resistance for long, slender beams is determined considering the elastic buckling moment; the resistance for short beams is limited by the plastic section capacity; and the effects of moment gradient in the member is considered in the resistance.

There are a number of differences that are of significance to the determination of the beam’s resistance. Figure 1 shows a comparison of the strength curves for a simply supported beam with equal end moments (Cb = 1) , loaded at the shear centre with λ = √Mp/Mr. The strength equations vary significantly in how they account for the region of inelastic buckling, whether determined through analytical or empirical means, or a combination of the two.


Figure 1: Comparison of international equations for uniform moment

The other noteworthy variations in the different strength equations involve how each handles deviations from the idealized conditions inherent in the classical derivation of the critical elastic buckling load. As well as inelastic response, these include initial imperfections, lateral and torsional restraint conditions, moment gradient and load placement.

One important factor for designers to note is that the standards change over time to reflect new research, changing practice, and other drivers. For example, the Canadian standard has included new methods of accounting for the effects of moment gradient, and the American specification has a new moment gradient factor for beams with only one flange braced that are subjected to double curvature bending. The engineer must always monitor the changes in the practice of structural design in the region that they practice, whether at home or abroad.

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