Experimental investigation of the structural behaviour of concrete-filled FRP tubes

Concrete-filled tubes (CFTs) are structural columns used to support compressive loads. A CFT takes advantage of the lateral confinement of the tube on the concrete core to increase the column strength. Since the development of CFT structures, steel has been the primary tube material. Over the last two decades however, fibre reinforced polymers (FRPs) have been increasingly used as tube materials because of their superior properties such as high specific strength and stiffness, superior corrosion resistance and good durability. This thesis describes a systematic experimental study of CFT columns with FRP as the tube material. This master’s project investigates the performance of FRP tubes of different properties and sizes. For this purpose, 12 CFT specimens with the length over diameter (L/D) ratios of 8 and 12, and diameter over tube thickness (D/t) ratios ranging from 11 to 43 were tested under compressive force with both ends of the columns set as pin joints. The experiments were carried out using a heavy loading machine and the experimental results are analysed in terms of strength and failure modes. The experimental results showed the significant improvements in column strength due to the confinement of the FRP tubes. It was demonstrated that while both L/D and D/t ratios influence column strength, D/t ratio plays a particularly important role in determining the column strength. The experimental results also showed the changes in failure modes with L/D and D/t ratios. To compare FRP tubes with plain concrete columns, an equivalent slenderness ratio for the CFT with FRP tube was derived. The equivalent slenderness ratio had good agreement with the D/t ration of the FRP tube. It was demonstrated that the equivalent slenderness can be used to determine the capacity of the CFT column using its D/t ratio.