Equivalent Uniform Moment Diagram Factor for Composite Columns in Minor Axis Bending

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Title: Equivalent Uniform Moment Diagram Factor for Composite Columns in Minor Axis Bending

Author(s): Timo K. Tikka and S. Ali Mirza

Publication: Structural Journal

Volume: 102

Issue: 1

Appears on pages(s): 120-130

Keywords: columns; composite construction; concrete; moment; slenderness ratio; steel

Date: 1/1/2005

Abstract:
The equivalent uniform moment diagram factor Cm was introduced into design practice to eliminate the need for extensive calculations, based on the solution to a differential equation, to compute the effect of moment gradient, along the column height, caused by unequal column end moments. The Cm expressions currently used by North American structural codes are based on the elastic behavior of columns, and do not include inelastic material behavior. This study was undertaken to determine the influence of different variables on Cm of slender, tied, rectangular composite columns in which steel shapes are encased in concrete and to examine existing expressions for Cm. Approximately 11,000 simulated columns, each with a different combination of specified values of variables, were used to generate the Cm data. The columns studied were subjected to short-term ultimate loads and unequal end moments causing moment gradient in single curvature and double curvature bending about the minor axis of the encased steel section. Two Cm design equations are proposed in this paper.