Study On Seismic Behaviors Of Concrete Filled Square Steel Tubular Frame Columns

Concrete filled steel tubular (CFT) structures are rapidly emerging as one of thedominant structural systems in the construction industry in recent decades due to theexcellent earth-quake resistant properties, particularly for the earthquake resistance.At the same time, strength and behavior of CFT structures have been investigated inmany countries. However, most of these researches are concentrated on concrete filledcircular steel tubular structures. Researches on concrete filled square steel tubular(CFSST) structures are lacking in contrast to concrete filled circular steel tubularstructures. Present theory of CFSST structures is mostly established on numericalcalculation results because of the lack of accumulation on the experimental results ofCFFST structures. The existing experimental results are varied from each other for thereason of difference of each experiment. So it is necessary to make more experimentalresearch on CFSST structures deeply.For the consideration of different sectional steel ratio, slenderness ratio and axialcompression ratio, nine concrete filled square steel tubular beam-columns with squaresections are tested under combined constant axial load and cyclic lateral loads in thepaper. The test results show that the hysteretic curves of the beam-columns are plumpin shapes and have no significant pinch phenomenon. That is to say the energydissipating ability of the CFSST columns was very well. The formulator for strengthof CFSST members under general situations is deduced based on the critical theory,and simplified calculation that can be referred to during design procedures is given.In this thesis, method for calculating load-deformation hysteretic curves of theCFSST columns is brought forward. A Fortran program is developed, and itsnumerical calculative curves have been verified by the tested curves. The numericalcalculative curves are in better agreement with the tested curves. Finally, the ductilityof the nine CFSST columns are calculated based on the restoring model applied, andinfluence of parameters such as sectional steel ratio, slenderness ratio and axialcompression ratio on the ductility of CFSST columns are analyzed.