Compressive Behavior of Prestressed High-strength Concrete-filled Aramid FRP Tube Columns: Experimental Observations

This paper presents an experimental investigation on the influence of prestressing fiber reinforced polymer (FRP) confining shell on the axial compressive behavior of high-strength concrete (HSC)-filled FRP tube columns. A total of 24 aramid FRP (AFRP)-confined concrete specimens with circular cross-sections were manufactured in the form of concrete-filled FRP tubes (CFFTs). The influence of the amount of prestress was examined by preparing the specimens with three different levels of lateral prestress ranging from 4.1 to 7.3 MPa. In addition to the prestressed specimens, companion specimens with no applied prestress were manufactured and tested to establish reference values. Results of the experimental study indicate that the influence of prestress on compressive strength is significant, with an increase in ultimate strength observed in all prestressed specimens compared to that of nonprestressed specimens. On the other hand, the influence of prestress on axial strain was found to be dependent on the amount of confinement, with lightly-confined and well-confined prestressed specimens displaying a decrease and increase in ultimate strain respectively, compared to their nonprestressed counterparts. The results also indicate that prestressing the AFRP shell prevents the sudden drop in strength, typically observed in FRP-confined HSC specimens, that initiates at the transition point that connects the first and second branches of the stress-strain curves. Finally, it was observed that prestressing the AFRP tube results in a significant increase in the specimen toughness as well as in the hoop strain efficiency of the AFRP shell.