Foam concrete-filled S600E stainless CFS built-up special shape columns: Tests, numerical and machine-learning investigations

Concrete-filled cold-formed steel (CFS) columns may brittlely fail if local buckling occurred of CFS components, which result in lateral confinement losses for the infilled concrete. Thus how to enhance the performance of CFS components is important. In this paper, a novel type of S600E stainless steel (SSS) with built-up closed special shape sections was proposed for enhancing the loading capacity instead of the normal cold-formed steel. Experimental and numerical simulation analyses were conducted for understanding the failure mechanism, confinement effects and ultimate capacity of foam concrete-infilled cold-formed S600E sorbite stainless steel composite columns. Finally, a data-driven machine-learning method is used for quick predicting the ultimate capacity of the columns, and the results are compared to the existing codes. The results of eight composite specimens indicate that the failure mode of composite specimens was still characterized by local buckling of the outer stainless steel and crushing of the core foam concrete, however, they exhibit a smooth transition in load-displacement curves before and after the peak load, indicating the favorable ductility. The results calculated from the Eurocode 4 were significantly overestimated, even though it was demonstrated good accuracy for foam concrete-filled normal CFS built-up special shaped sections by the authors’ previous work, and the DBJ/T 13–51 in China exhibited more accurate. An ultimate capacity prediction formula is proposed taking into account the yield strength of sorbite stainless steel and the confinement effect coefficient, and the errors were less than 15% compared to tests, and the results of different sections are compared with the ML-based results to verify its reliability and applicability.