ABSTRACT
The compressive strength of concrete under tri-axial compression is much higher than that in uni-axial compression. This advantage is utilized in infilling concrete into tubes made of different materials and served as the members subjected mainly to compression. These kinds of members make use of the composite properties of both the concrete core and outer tube in complex stress conditions, so that the advantages would be developed sufficiently and the load bearing capacity enhanced. The most common tube materials are steel and fiber reinforced polymer (FRP), into them the concrete is filled to construct the composed columns (Han 2004, Cai, 2003, Amir et al. 2000, Omar & Shahawy 2000, Amir & Rizkalla 2001). In recent years, a new system, concrete filled CFRP-steel tube (Wang & Zhao 2003, Gu 2007) has been proposed and investigated experimentally and theoretically.
