Determination of the Buckling Critical Load for Composite Concrete-Filled Steel Tube Columns from Partial Experimental Data: A Review of the Southwell Plot Technique

This paper discusses two techniques that target the determination of the buckling critical load for composite concrete-filled steel tube (CFT) cantilever columns from partial or incomplete experimental axial load - lateral displacement (P-Δ) data. The numerical techniques evaluated in this study are the secant approach (better known as the Southwell plot) and the tangent approach. The motivation of this study arises from the inability of a sophisticated laboratory system to reach the experimental peak buckling capacity of some full-scale composite CFT specimens during compression tests. The review of these two techniques is validated against an experimental dataset of CFT specimens. In addition, these two techniques are evaluated through numerical nonlinear analysis of composite CFT columns with different values of slendernesses and initial imperfections. The evaluation with both the available experimental dataset and the parametric study confirms the scope and limitations of these two techniques. The application of the secant approach allows a more accurate determination of the critical load for those composite CFT columns where the laboratory system is not capable to reach their buckling capacity.

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