Experimental investigation on concrete-filled steel tubes with reinforcing bars under axial and eccentric tension

Experimental investigation under axial and eccentric tension was conducted on concrete-filled steel tubes with reinforcing bars inside having length of 4 m for researching its loading process and failure mode. The load-axial displacement curve, load-strain curve, tensile bearing capacity and rigidity of specimens were obtained and were compared with hollow steel tubes and concrete-filled steel tubes having the same geometric dimensions. Research results show that the inner reinforcing bars can increase the tensile bearing capacity and rigidity of the specimen and it can reach yielding stage when the specimen reaches its bearing capacity; the existence of core concrete makes the outer steel tube in the state of biaxial stress and hence the tensile bearing capacity of concrete-filled steel tubes are increased. The tensile bearing capacity of concrete-filled steel tubes are 13% and 15% higher than that of hollow steel tubes respectively. On the basis of test, the calculation formula of bearing capacity and stiffness of tested specimens under axial and eccentric tension were put forward and the calculated results agreed well with the experimental results.