Compressive behaviour of stub composite columns with stainless steel square outer tubes and recycled aggregate concrete

In recent years, stainless steel has been increasingly used in construction practices due to its appealing appearance, high strength, and satisfactory corrosion resistance, which contribute to a long lifespan. Stainless steel hollow sections are extensively employed as structural members. This paper investigates the axial compressive behaviour of stub composite columns with stainless steel square outer tubes and different aggregate concrete. An experimental programme involving 12 specimens was conducted to study the effects of cross-sectional dimensions, and the types and sizes of coarse aggregates. The load-bearing capacity and failure modes of the specimens were recorded and analysed. A comprehensive parametric study was performed, examining three stainless steel types, different cross-sectional dimensions and two concrete grades. The result showed that while the types and sizes of coarse aggregates influenced the compressive strength of concrete, aggregate sizes of 10 mm and 20 mm did not significantly impact the axial compressive strength of concrete-filled stainless steel composite columns. The axial compressive capacity of concrete-filled stainless steel columns was significantly influenced by the type of stainless steel and the cross-sectional width-to-wall thickness ratio. A simple formula is proposed to predict the cross-sectional compressive capacity of concrete-filled stainless steel columns.