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.