Local and post-local buckling behavior of welded square high-strength steel tubes with concrete-infilled restraints

Concrete-filled high-strength steel tubular members gain increasing popularity as the building height and bridge span increase. The slender sections and higher stress levels, however, make the high-strength steel plates more susceptible to local buckling. This paper reports an experimental and numerical investigation on local and post-local buckling behavior of welded square high-strength steel tubes with concrete-infilled restraints. Sixteen high-strength steel tubes with nominal yield strengths of 460, 500, and 550 MPa with concrete-infilled restraints were tested. The experimental results reveal that the post-buckling reserve strength of steel tubes with slender sections increases with the increase in plate slenderness regardless of steel grade. A total of 168 numerical models were subsequently established using the verified finite element method. Based on the finite element analysis results, the slenderness limits and effective width formula were proposed for both high-strength and normal-strength steel tubes with concrete-infilled restraints. Available test data of steel-only-loaded concrete-filled steel tubular specimens constitutes an experimental database to evaluate the reliability of the existing slenderness limits and effective width formulas. The comparison result shows that GB 50936, AS/NZS 2327, and AISC 360-16 overestimate the slenderness limits, while Song et al. underestimate the slenderness limit excessively. The proposed slenderness limit (lambda(pl) = 0.500) is more consistent with the experimental results with a reasonable conservative level. The mean ratio of predicted post-buckling strengths by the proposed effective width formula to experimental results is 0.94, with a standard deviation of 0.073. The proposed slenderness limit and effective width formula provide a more accurate prediction and, therefore, are recommended in design.