Durability of Hollow-Core GFRP-Concrete-Steel Columns under Severe Weather Conditions

One of the emerging applications of fiber-reinforced polymer (FRP) tubes is hollow-core FRP-concrete-steel (HC-FCS) columns. HC-FCS columns demonstrate superior advantages in material savings and mechanical behavior. However, the lack of long-term data for their durability performance hinders their greater acceptance. This study aims to investigate the degradation of HC-FCS cylinders under combined freeze-thaw, heating-cooling, and wet-dry cycles. Sustained axial loads were also applied to the cylinders during environmental conditioning to simulate the service dead load. Compression tests on cylinders were performed and split-disk tensile tests were performed on FRP rings for both conditioned and control specimens. The test results showed that the environmental conditioning slightly degraded the strength and vertical strain capacities of the HC-FCS cylinders, but caused pronounced degradation of the hoop strain capacities of the glass fiber-reinforced polymer (GFRP) tube. Investigating the microstructure of the FRP before and after conditioning revealed that no chemical reaction took place. However, damage to the interphase of fiber and resin led to damage of the fiber bond. This led to strain concentration and early rupture of the FRP. The sustained load had a negative effect on the cylinders, but had a more obvious effect on strain than on strength.