عنوان مقاله [English]
Composite columns\ have\ been\ used\ in\ constructions\ for\ many\ years\ \ due\ \ to\ \ their \ \ advantages\ over\ \ ordinary\ columns. Concrete filled steel tubes, CFST are one such column. Some of the advantages of these types of column are known as; not needing molding, high ductility, relatively high resistance with low volume properties, low deformation capability relative to ordinary steel columns and, most commonly, economic potential.Due to these enormous potentials, a general research program was launched to investigate CFST's in an experimental manner. This program was planned and done in the IIEES structural lab in Tehran, Iran. In order to achieve the goals of the project, ten specimens were constructed using a 1:3 scale and were tested as cantilever columns. Specimens were loaded under a constant axial load, while laterally loading under an enhancing lateral cyclic load based on a displacement controlled condition.Three distinct geometrical shapes namely, square; circle and octagonal sections were considered and tested. Specimens were also tested using stiffeners in comparison to specimens without stiffeners. This paper presents the results obtained and ways and methods of achieving the goals of the project.Using stiffeners inside a steel tube in the critical zone, significantly improves column behavior and ductility.