Code based assessment of load capacity of steel tubular columns infilled with recycled aggregate concrete under compression

In this study, a comparison and code evaluation for the load carrying capacity (Pu) of recycled aggregate concrete (RAC) filled steel tubular short columns under axial compression are presented. For this, a total of 1600 Pu results were assessed using four different international design codes (Eurocode 4, ACI, AIJ and DL/T). The relations as well as the proposed formulas extracted from the study were discussed. For the composite column, the properties of the steel tube such as outer diameter (D), wall thickness (t), length (L) and yield strength of steel (fy) as well as the properties of core concrete such as single and combined used of recycled coarse and fine aggregates, substitution level and compressive strength were considered as the investigation parameters. Moreover, the strength of the recycled aggregate self-compacting concrete was adopted from an experimental study reported in the literature. It was found that Eurocode 4 had revealed better results in terms of randomness and scatter of data; whilst the strength values calculated via ACI had relatively more variation than other codes. In addition, the analysis of the results indicated a shortcoming especially in ACI due to not considering the benefit of the confinement between the steel tube and infill. The effect of the yield strength of steel tube was observed to be varied based on D/t ratio. Furthermore, in all tested codes, the incorporation of recycled aggregate adversely affected the concrete strength which in turn decreased the predicted Pu of the columns.