Flexural behavior of hybrid FRP-concrete-steel double-skin tubular beams with PBL shear connectors.

• Four-point bending tests on eight DSTBs with different inner steel tube shapes, PBL types and arrangements. • Slip became prominent after yielding of steel tube bottom surface. • Specimens with square steel tubes had higher load capacities than circular tubes. • Specimens with foams between PBLs had the maximum slips. Hybrid fiber-reinforced polymer (FRP)-concrete-steel double-skin tubular beams (DSTBs) have a very ductile load–deflection response but may experience a relatively large slip between the concrete and the inner steel tube. Perfobond (PBL) shear connectors, which have a perforated steel plate with transverse reinforcing bars passing through the perforations, are widely used to enhance the bond performance between the concrete and the steel section for composite beams. In this study, for the first time, PBLs are employed in hybrid DSTBs to tackle the excessive slip problem. Four-point bending tests are performed on eight hybrid DSTBs with two cross-sectional shapes of inner steel tubes, two types of PBL plates, and four different PBL arrangements. Results identify that a typical load–deflection curve consists of three segments: an initial linear segment up to the yielding of steel tube bottom surface, a hardening segment, and an almost flat load plateau segment. The slips between concrete and steel tubes increase in a faster rate when yielding occurs at steel tube bottom surface. Overall, specimens with PBLs placed along the full span have the smallest slips (around 0.2 mm), whereas maximum slips occur for specimens with foams inserted at the spacings between PBLs (i.e., 2.33 and 0.59 mm for specimens with a circular and a square steel inner tube respectively). PBL shear connectors have efficiently reduced the slip, when comparing with the results of some hybrid DSTBs in previous studies. [ABSTRACT FROM AUTHOR]