Siress-strain behavior of concrete-filled square steel tubes

This paper introduces the stress and strain behavior of concrete-filled square hollow section (SHS) steel tubes based on our 36 specimen tests. The research is mainly the numerical analysis on the strains measured from the tests. From the analysis, the forces carried by square steel tubes are parted from the total external loads, and their whole deformation profiles are also separated from the total. Then discussion is carried out on the ultimate strength of concrete confined by square steel tubes. It is found that steel tubes do provide some confinement and cause an increase of concrete strength, the amount is determined by the amount of confinement. At the same time, the vertical stress of the steel tubes will be lower then their yielding stress because of their horizontal confinement to concrete. The suggested ultimate strength is compared with the test results both from this paper and from available references in public domain; good correlation is achieved.