Strengthening schemes of special-shaped concrete-filled steel tubes: A review

Nowadays, special-shaped concrete-filled steel tubes (SCFSTs) are popular in the construction industry because they have a similar limb size as the wall and can easily be embedded in walls, eliminating convex corners and improving the interior room space. They possess high compression capacity, more construction efficiency, and better seismic performance than special-shaped reinforced concrete columns. However, the initially developed SCFSTs would show inferior mechanical performance due to the limited confinement of infilled concrete. To resolve this issue, many strengthening techniques were recommended i.e., (1) apply stiffeners on the internal surface of steel walls; (2) connect mono CFSTs via different shear connectors; (3) divide the tube's cross-section into multiple steel cavities. The influence of these techniques on local buckling, failure behavior, compression capacity, energy dissipation performance, and ductility of SCFSTs under different loadings has been examined during the last decades using experimental, numerical, and analytical studies. However, a detailed comparative analysis of strengthening schemes on the performance of SCFSTs is still missing. This article aims to review the available SCFSTs regarding cross-sectional shapes, strengthening techniques, loading conditions, and many geometric and material parameters. The design methods specified in AISC, EC4, CECS, and GB are evaluated for their reliability and applicability for predicting the concentric and eccentric compression capacities of SCFSTs. In addition, the study covers the actual applications of SCFSTs in various engineering projects. Eventually, conclusions, the current knowledge gap, and future research suggestions on SCFSTs are presented and discussed.