Structural performance of welded built-up square CFST stub columns

A welded built-up square tube is made by flare welding 4 thin steel plates, which are bent to form L-shape. When it is used for a CFST column, the ribs placed at the center of concrete and steel tube width prevent local buckling and the tube confines concrete to improve its structural load capacity. In this study to introduce how to build welded built-up square columns and to evaluate the structural capacities of welded built-up square steel tubes and CFST columns, 15 full-size specimens were fabricated for structural test with various types of steel tubes (welded built-up square tube and generic steel tube), width–thickness ratio (B/t=50, 58 and 67) and concrete strength (Fck=10 MPa and 40 MPa) to verify sectional efficiency and structural superiority inherent in welded built-up square columns.