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\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$L/D=3.25$$\end{document} 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\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$L/D=3.25$$\end{document} and has little influence on ultimate displacement, contrary to the columns with L/D=6\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$L/D=6$$\end{document}. 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\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$L/D=3.25$$\end{document} is better than that of columns with L/D=6\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$L/D=6$$\end{document}. 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.