Seismic Performance of Precast Posttensioned Segmental FRP-Confined and Unconfined Crumb Rubber Concrete Columns

Abstract

This paper presents an experimental study carried out on unbonded posttensioned (PT) segmental precast concrete columns. In total, eight cylindrical columns were posttensioned and tested under incrementally increasing reverse cyclic loading. The columns consisted of four concrete cylindrical segments that were assembled on top of each other with dry joints. PT bars were passed through a hole cast into the center of the segments, left unbonded, and anchored to the column loading head on the top and footing on the bottom. The variables in this study were the level of posttensioning, concrete material type, and concrete confinement. Two different levels of posttensioning force of 50 and 100 kN, corresponding to an average axial stress on the concrete of 2.83 and 5.77 MPa, were applied to the columns. Conventional concrete and crumb rubber concrete (CRC) were considered to investigate the effect of concrete material on the behavior of the segmental column. The concrete confinement effect was investigated by confining the bottommost segment using fiber-reinforced polymer (FRP) wraps. The results of this study showed that FRP-confined CRC segmental columns could provide an environmentally-friendly alternative to conventional concrete columns in structural applications. The effect of the confinement on the strength of rubberized concrete was higher than that of the conventional concrete. The negative effect of the rubber particles on the strength reduction in the concrete at the structural level was much lower than that in the concrete at the material level. Increasing the column posttensioning force increased the measured peak load and decreased the ultimate drifts for both unconfined and FRP-confined specimens. This paper also concluded that in unbonded PT columns in order to ensure a fully self-centering behavior, the level of axial stress ratio must be limited.