Structural behaviour of recycled aggregate concrete filled steel tube columns strengthened by CFRP

► The structural behaviour of recycled aggregate concrete filled steel tube columns. ► The enhancement on the load carrying capacity and stiffness by CFRP wrapping. ► The influence of the tube cross-sectional configurations on structural behaviour. ► The theoretical calculations of the bearing capacity of the composite columns. This paper presents experimental research on structural behaviour of normal and recycled aggregate concrete filled steel tube (RACFT) columns externally strengthened with carbon fibre reinforced polymer (CFRP) sheets and subjected to axial loading. A total of 22 specimens were tested to investigate the influence of the following variables: (1) tube configurations, circular or square, solid or hollow; (2) types of concrete, normal or recycled aggregate concrete; and (3) strengthening arrangements, full wrapping or partial wrapping. The results show that the recycled aggregate concrete may degrade the concrete strength during the curing period for the first 28days. However, the ultimate strength and stiffness (90-day curing period) for the square and circular solid steel tubes filled with recycled aggregate concrete show slightly higher values than the ones filled with normal concrete, but this is reversed for the steel hollow section tubes. The test results indicate that both reinforcing arrangements enhance the ultimate strength greatly in comparison to the control column, and that the full wrapping arrangement is much more effective than the partial wrapping one. Moreover, stiffness of the strengthened columns is increased significantly due to the restraint offered by the external CFRP wrapping on hoop deformations during compressive loading. In addition, theoretical calculations of the bearing capacity of the composite columns are presented and compared with the experimental results.