Effect of cross-stiffening parameters and discontinuities on axial performance of large-scale CFSTs

Concrete-filled steel tubes (CFSTs) are extensively used in modern construction. Large-scale square CFST columns typically incorporate cross stiffening per construction specifications, yet its structural contribution is not accounted for in current design codes. Cross stiffening improves steel tube boundary conditions, enabling relaxed width-to-thickness ratio limits and reduced steel consumption. It also restrains concrete expansion through tensile resistance, thereby enhancing axial compression performance. Meanwhile, the effect of stiffening discontinuities on column performance remains uninvestigated. This paper examined these gaps through experimental testing of 12 large-scale square CFSTs. Based on experimental results, corresponding finite element models were established and validated. The failure modes, load-longitudinal strain curves, key indicators, and strain/stress distributions were systematically investigated. Research demonstrates that cross-stiffened square CFSTs can accommodate width-to-thickness ratios twice the current code limits when employing stiffening thickness of 0.75 times the tube thickness. For Q355 steel, this approach reduces steel consumption by approximately 29%. Experimental and numerical results indicate that a discontinuity distance of 1/8 B (where B is the section width) has negligible influence on the axial compressive behavior of square CFST columns with cross-stiffening. A calculation method for determining the axial bearing capacity of square CFSTs with cross stiffening was proposed based on the Mander confined concrete model, showing good agreement with experimental (within ±5%) and numerical results (within ±10%).