Experimental Study on the Behavior of Recycled Concrete-Filled Thin-Wall Steel Tube Columns Under Axial Compression

In order to study the axial compression performance of recycled concrete-filled bolted thin-wall steel tube and the constraint effect of steel tube on different recycled aggregate concretes (RACs), a total of 12 composite square columns with two different length-to-side ratios (L/D) and three kinds of concrete were tested. Results are shown as follows: the most serious buckling behavior of columns with L/D = 3.25 and 6 is different, and the buckling degree is in relation to type of concrete. All the composite columns which depict three stages in their load-axial compression behaviors enter yield stage in 75% ultimate load. The type of concrete has great influence on the ultimate load-carrying capacity of columns with L/D = 3.25 and has little influence on ultimate displacement, contrary to the columns with L/D = 6. There exist three representative performance points in the load-axial strain curves of steel tube. The constraint effect of steel tube on RAC with recycled brick aggregate (RBA) is the best, which of columns with L/D = 3.25 is better than that of columns with L/D = 6. Some equations (e.g., Eurocode 4, Giakoumelis and Lam's, and Xiao et al.) considering concrete confinement are suitable for calculating the load-carrying capacity of RCFTST using RBA. The internal curing effect of clay brick makes the performance of composite columns improve significantly.