Circular hybrid double-skin tubular columns with a stiffener-reinforced steel inner tube and a large-rupture-strain FRP outer tube : compressive behavior

Abstract

A typical fiber-reinforced polymer (FRP)-concrete-steel double-skin tubular column (DSTC) consists of an FRP outer tube, a hollow steel inner tube and an annular concrete in-fill in between. The existing studies on DSTCs in the past decade have generally confirmed the good structural performance of such column form, while it is worth noting that the possible in-ward buckling of the steel tubes in DSTCs is still a problem to be addressed, especially when DSTCs are subjected to large axial deformation. Against this background, a variation form of DSTCs called R-DSTCs has been recently developed by the authors. An R-DSTC is a DSTC in which the steel inner tube is reinforced by vertical stiffeners on the outer surface and the FRP outer tube can be circular, square or rectangular. The present paper presents the first ever experimental study on the compressive behavior of circular R-DSTCs which is the most common form of DSTCs. For the circular R-DSTC specimens tested in the present study, the outer tubes are made of a type of large-rupture-strain FRP. The vertical stiffeners on the steel inner tube are expected to delay or restrain the inward buckling of the steel tube, and the large-rupture-strain FRP outer tube makes possible a relatively large axial deformation of the specimen. In total, two DSTC specimens, twelve R-DSTC specimens and three bare steel tubes with/without stiffeners were tested, with the studied parameters covering the quantity, the dimensions and the shape of the stiffeners and the thickness of the FRP outer tube. The test results showed that R-DSTC specimens had a much better performance than the corresponding DSTC specimens in terms of both axial loading capacity and ductility, due to the existence of vertical stiffeners on the steel inner tube of R-DSTCs. The effects of the vertical stiffener-related parameters on the compressive behavior of R-DSTC specimens were also carefully examined and discussed in details.