Study of compressive behaviour of FRP-recycled aggregate concrete-steel stub columns

Fibre-reinforced polymer (FRP) recycled aggregate concrete (RAC)-steel columns are a proposed novel form of composite based on hybrid FRP-concrete-steel double-skin tubular columns and, combined with RAC, greatly benefit our sustainable resources and fully exploit the advanced mechanical properties of every component of these composites. To gain an in-depth understanding of the compressive behaviour of FRP-RAC-steel columns (FRSCs) and to examine whether the existing bearing capacity models for other confined concrete columns are applicable to FRSCs, 15 basalt FRSCs were tested by subjecting them to monotonic axial compression. The main parameters investigated were the diameter-to-thickness ratio of the steel tube and the recycled coarse aggregate (RCA) replacement ratio. The test results showed that the compressive behaviour of FRSCs generally enhanced with a decrease in the diameter-to-thickness ratio of the steel tube, and that the FRSCs with RCA replacement ratios of 30% and 70% tended to have better ultimate bearing capacity and axial shortening. Three typical stress-strain models were checked to predict the ultimate bearing capacity of FRSCs, and values calculated from Yu's model coincided well with the test results.