Shift of Effective Centroid of Channel Columns

Abstract

In the design of pin-ended channel columns, it is necessary to account for the shift of the effective centroid caused by local buckling. The current American Iron and Steel Institute's 1996 Specification for the Design of Cold-Formed Steel Structural Members and the 1996 Australian/New Zealand standard Cold-Formed Steel Structures calculate the shift by use of effective widths. However, the ability of the effective width rules to accurately predict this shift has not been experimentally assessed. In this paper, recent tests on fixed-ended channel columns are used to obtain values of the shift of the effective centroid, including its variation with the applied load. It is concluded that effective width rules of the American and Australian specifications accurately predict the direction and magnitude of the shift of the effective centroid for plain channels but not for lipped channels with slender flanges. The paper proposes simple modifications to the current effective width rules that provide agreement between the measured and predicted shifts of the effective centroid for lipped channels. The modifications are shown to produce more accurate design strengths for lipped channel columns.