Axial compression behavior of recycled-aggregate-concrete-filled GFRP-steel composite tube columns

Aiming to expand the structural applications of recycled aggregate concrete (RAC), the innovative approach of using the hybrid form of RAC-filled glass-fiber-reinforced polymer (GFRP)-steel composite tube columns (RACFCTs) is particularly striking because of their optimal combining of fiber-reinforced polymer (FRP), RAC and steel. The existing research relevant to RACFCTs is limited and is mainly concerned with seismic performance. This paper presents the first-ever axial compression test on RACFCTs having three different slenderness ratios ranging from 20 to 40; the effect of the recycled coarse aggregate (RA) replacement ratio is also examined. The main performance aspects evaluated in this study were the failure mode, ultimate condition, axial load-lateral deflection curves, load-strain curves, and dilation behavior. The test results clearly show the benefit of the GFRP-steel composite tube on the compression behavior of the columns. The test results also demonstrate that the RACFCTs with a high RA replacement ratio and a high slenderness ratio had more ductile behavior. Finally, a design equation for predicting the maximum capacity of RACFCTs was derived, and its applicability was examined. The proposed formula produced a close estimate of the test results.