Session Start Date

10-15-1998

Abstract

The buckling behaviour of cold-formed steel columns and beams is far from simple. The three generic forms of buckling, namely local buckling, distortional buckling and overall buckling, generally have different wavelengths and are usually restricted to different span ranges. However, there is also the possibility of interaction among these buckling modes at a certain span length. Thus, local plate buckling and distortional buckling may occur together with lateral-torsional buckling in such a way that they all have an influence on the ultimate load carrying capacity of a member. The influence of local buckling is taken into consideration in design codes by using either an effective width or an effective thickness for the plate element under consideration. However, the consideration of distortional buckling is less-well developed in the codes and the effect of its interaction with other buckling modes is far from clear. Another factor which influences the ultimate load carrying capacity of a thin-walled section is the interaction of compression force and bending moment. In current design codes, this is usually limited by a certain allowable stress in the extreme fibres of the cross-section. For a stocky member which is not subject to buckling, this is a reasonable assumption. However, for potentially unstable members, the behaviour is complicated and, in most cases, the test results are scattered high above the predictions given by the design codes. Generalised Beam Theory (GBT) [1-3] can provide explicit analytical expressions for the problems associated with the various interactions of the alternative buckling modes and also the interactions associated with combinations of axial load and bending. This paper, therefore, makes particular use of GBT in assessing the influence of local buckling and distortional buckling on lateral-torsional buckling and the interaction of compression force and bending moment. Based on analyses using GBT together with comparisons with available test results, conclusions are presented which the authors hope will be of benefit for future design codes.

Department(s)

Civil, Architectural and Environmental Engineering

Research Center/Lab(s)

Wei-Wen Yu Center for Cold-Formed Steel Structures

Meeting Name

14th International Specialty Conference on Cold-Formed Steel Structures

Publisher

University of Missouri--Rolla

Publication Date

10-15-1998

Document Version

Final Version

Rights

© 1998 University of Missouri--Rolla, All rights reserved.

Document Type

Article - Conference proceedings

File Type

text

Language

English

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Oct 15th, 12:00 AM

Buckling Mode Interaction in Cold-formed Steel Columns and Beams

The buckling behaviour of cold-formed steel columns and beams is far from simple. The three generic forms of buckling, namely local buckling, distortional buckling and overall buckling, generally have different wavelengths and are usually restricted to different span ranges. However, there is also the possibility of interaction among these buckling modes at a certain span length. Thus, local plate buckling and distortional buckling may occur together with lateral-torsional buckling in such a way that they all have an influence on the ultimate load carrying capacity of a member. The influence of local buckling is taken into consideration in design codes by using either an effective width or an effective thickness for the plate element under consideration. However, the consideration of distortional buckling is less-well developed in the codes and the effect of its interaction with other buckling modes is far from clear. Another factor which influences the ultimate load carrying capacity of a thin-walled section is the interaction of compression force and bending moment. In current design codes, this is usually limited by a certain allowable stress in the extreme fibres of the cross-section. For a stocky member which is not subject to buckling, this is a reasonable assumption. However, for potentially unstable members, the behaviour is complicated and, in most cases, the test results are scattered high above the predictions given by the design codes. Generalised Beam Theory (GBT) [1-3] can provide explicit analytical expressions for the problems associated with the various interactions of the alternative buckling modes and also the interactions associated with combinations of axial load and bending. This paper, therefore, makes particular use of GBT in assessing the influence of local buckling and distortional buckling on lateral-torsional buckling and the interaction of compression force and bending moment. Based on analyses using GBT together with comparisons with available test results, conclusions are presented which the authors hope will be of benefit for future design codes.