Hybrid double-skin tubular columns with a large rupture strain FRP outer tube: stub column tests

Hybrid fiber-reinforced polymer (FRP)-concrete-steel double-skin tubular columns (DSTCs) consist of an outer tube made of FRP and an inner tube made of steel, with the space between filled with concrete. A significant amount of research has been conducted on hybrid DSTCs with an outer tube made of glass FRP (GFRP), carbon FRP (CFRP), or aramid FRP (AFRP). One important finding of the existing research is that the ductility of the column depends significantly on the rupture strain of the FRP tube, among other factors. Against this background, this paper presents an experimental study where hybrid DSTCs with a large rupture strain (LRS) FRP tube, namely, polyethylene terephthalate (PET) FRP tube, were tested under axial compression. PET FRP composites have emerged recently as an economical and environmentally friendly material with a rupture strain of over 7%. Results from a total of four DSTC specimens are presented, with the main test variable being the thicknesses of the steel tube. The test results confirmed the ample ductility of the column and suggested that the diameter-to-thickness ratio of the inner steel tube is a more critical parameter in such DSTCs than in DSTCs with a GFRP, AFRP or CFRP outer tube.