Experimental and numerical investigations of circular recycled aggregate concrete-filled stainless steel tube columns

This paper reports a comprehensive experimental and numerical study of the flexural buckling behaviour and resistances of circular recycled aggregate concrete-filled stainless steel tube columns. The experimental programme, adopting four series of column specimens designed with various stainless steel tube sizes, recycled coarse aggregate replacement ratios and member lengths, included material tests on both recycled aggregate concretes and stainless steel tubes, initial global geometric imperfection measurements and pin-ended column tests. The obtained experimental results, including the failure loads, load–mid-height lateral deflection curves and flexural buckling failure modes, were reported in detail. The effects of the stainless steel tube size, recycled coarse aggregate replacement ratio and member length on the flexural buckling resistances of the column specimens were examined. The lateral deflection distributions along the column specimen lengths and the development of the longitudinal strains of the outer stainless steel tubes were discussed. The experimental programme was supplemented by a numerical modelling programme, in which finite element models were developed and validated against the test results and then used for conducting parametric studies to generate further numerical data over a wide range of cross-section dimensions and member lengths. Given that there have been no existing design codes for recycled aggregate concrete–stainless steel composite structures, the relevant codified design rules for circular natural aggregate concrete-filled carbon steel tube columns failing by flexural buckling, as used in Europe, Australia/New Zealand and America, were assessed for their applicability to circular recycled aggregate concrete-filled stainless steel tube columns, based on the test and numerical data. The assessment results revealed that the design rules, as given in the Australian/New Zealand standard and American specification, result in unsafe flexural buckling resistance predictions when used for circular recycled aggregate concrete-filled stainless steel tube columns, while the Eurocode design rules lead to more safe and accurate flexural buckling resistance predictions.