Effect of shape section properties on ultimate strength of concrete filled multi-skins steel tube column under various load

An experimental investigation was performed to estimate the ultimate strength ratio of square and circular concrete-filled multi-skin steel tubes (CFMST). In this study, 18 composite column specimens were designed and tested experimentally under axial and eccentric loads. The CFMST columns are divided according to their cross section into two groups, circular and square. Each group is divided into three subgroups according to the type of loading (e/h=0, e/h=1, an d e/h=2), and each group contains three columns, a column containing (one, two layers, three layers). The external dimensions of both sections are the same. Some geometrical parameters were investigated both experimentally and theoretically in order to explain their effect on the ultimate strength of CFMST columns. A variety of steel layers, loading types, and other parameters were investigated. It is observed that the ultimate strength of a square section is greater than a circular section experimentally by (21.05, 22.22 and 54.53) % under axial load and (10,23.81 and 16.67) % to(e/h=1), and it1s also increased by (21.43,15 and23.53) % for (one to three layers). While theoretically, it was found that the ultimate strength of circular section increases the ultimate strength of the square section by (4.37, 3.44 and13.01) % under axial load, (13.1, 2.19 and 7.83) % under eccentric load(e/h=1), and (4.07, 9.15, and2.41) % under eccentric load(e/h=2) for (one to three layers).