Compressive behaviour of large rupture strain FRP-confined concrete-encased steel columns

Fibre-reinforced polymer (FRP)-confined concrete-encased steel columns (FCSCs) have emerged as a new form of hybrid columns. An FCSC consists of an outer FRP tube, an inner steel section, and concrete filled in between. The concept of FCSCs not only provides a durable and ductile structural form for new construction, but also can be practiced as an effective method for the retrofitting/strengthening of existing steel columns. This paper presents the first ever study on FCSCs with a large rupture strain (LRS) FRP tube [i.e., polyethylene terephthalate (PET) FRP tube]. A total of 12 circular specimens (six FCSCs and six FRP-confined concrete columns) were tested, with the main test variable being the thickness of the PET FRP tube. The test results showed that the buckling of the encased steel section can be well prevented by the constraint from the surrounding FRP-confined concrete even when the axial deformation is large. On the other hand, the encased steel section can provide additional confinement to the concrete in FCSCs, leading to excellent structural performance of the columns in terms of both axial strength and deformation capacity.