Axial compressive behaviour of circular FRP-confined multi-tube concrete columns

A new form of hybrid structural column that has improved corrosion resistance and that can enhance the compressive strength and ultimate strain of concrete is the fibre-reinforced polymer (FRP)-confined multi-tube concrete column (MTCC) system. Existing research on MTCCs has been limited to glass FRP (GFRP) outer tubes with internal steel tubes and normal-strength concrete. This paper reports an experimental study on 22 circular MTCCs that are loaded under monotonic axial compression. Five main column parameters are investigated, namely internal tube material, internal tube configuration, concrete strength, fibre type, and FRP tube thickness. The test results show the excellent structural behaviour of MTCCs for both the normal- and high-strength concretes. The MTCCs with internal steel tubes outperformed those with aluminium internal tubes in terms of load carrying capacity. MTCCs confined with basalt FRP and GFRP jackets both performed well, while an increasing of FRP thickness improved the ultimate strength and axial strain capacity of the column. An analytical model based on the transformed section approach is also used to predict the axial load-strain behaviour of the MTCC specimens. The model provides satisfactory predictions of the test results.