Overall stability capacity design of T-shaped irregularly concrete-filled steel tube columns considering axial compression and any directional moments

A slender T-shaped irregularly concrete-filled steel tube column (T-ICFSTC) may be subjected to overall instability failure under combined axial load and moment. But current research is not available about a complete design of T-ICFSTCs subjected to axial compression and any direction bending moments because of a complicated parameter study involved in the analysis. This paper investigates the overall stability capacity performance and design prediction of the T-ICFSTCs that are formed by I-shaped steel, U-shaped steel and several cell infilled concrete. First, the finite element model for analyzing the overall instability performance and failure is established and verified by the previously experimental tests carried out by the authours. Then, the overall stability capacity of T-ICFSTC around its symmetric axis is investigated numerically and accordingly design formulas of & phi;y-& lambda;ny are established. In particular, interaction influence between initial imperfection direction and applied bending moment direction is studied, thus resulting in a critical initial imperfection direction relatively to applied bending direction. Sequently, the loadbearing capacity and performance under any direction bending moments are explored numerically and the normalized design curves reflecting interaction of N-M and Mx-My at their limit states are formulated by fitting the FE results of examples. Finally, a complete set of overall stability prediction formulas of T-ICFSTCs under combined axial load and any directional bending moment are established and the results obtained agree well with FE numerical investigation results.