Axial Compressive Behavior of Circular High-strength Concrete-filled FRP Tubes

Concrete-filled fiber-reinforced polymer (FRP) tubes (CFFTs) have received significant research attention over the last two decades. However, experimental studies on the behavior of CFFTs filled with high-strength concrete (HSC) remain very limited. This paper presents the results of an experimental study on the axial compressive behavior of 83 monotonically-loaded circular CFFTs. The effects of fiber type, concrete strength, specimen size, and manufacturing method on the compressive behavior of CFFTs were investigated. The CFFTs were manufactured with carbon FRP (CFRP), high-modulus CFRP (HMCFRP), or aramid FRP (AFRP) tubes, and their average unconfined concrete strengths ranged between 34-110 MPa. The diameters of the test specimens ranged from 75-300 mm with all specimens maintaining a 2:1 height-to-diameter ratio. The effect of the CFFT manufacturing method was investigated through AFRP specimens that were manufactured through either an automated filament winding or manual wet layup technique. The experimentally recorded stress-strain relationships are presented graphically and the ultimate axial stresses and strains and hoop rupture strains are tabulated. The large quantity of the results presented in this paper allows for a number of significant conclusions to be drawn. The results clearly indicate that over a certain confinement threshold, high-strength CFFTs (HSCFFTs) exhibit a highly ductile behavior. However, for the same nominal confinement ratio, compressive behavior of CFFTs degrades as concrete strength increases. The results also indicate that the compressive behavior of CFFTs is significantly influenced by the manufacturing method and fiber type with an improvement in compressive behavior linked to an increase in fiber rupture strain. Finally, the influence of specimen size was found to be negligible for the range of diameters tested in this study. Further experimental observations on these and other key parameters are presented and discussed in the paper.