Experimental research on concrete-filled square steel tubular columns stiffened with PBL

Experimental study on concrete-filled square steel tubular columns stiffened with PBL under axial compression was conducted to research its failure mode and load carrying capacity. 23 specimens with different widthto-thickness ratio,stiffener type,circular hole diameter and spacing were designed and tested. After comparing their failure mode,bearing capacity,stiffener stiffness,and ferrule effect,it is found that: stiffener stiffness is a key factor to the failure mode of concrete-filled square steel tubular columns stiffened with PBL; when the minimum stiffening is met,along transverse wallboard the lateral buckling wave length is shorter or even becomes ‘double wave'; along longitudinal wallboard the lateral buckling wave length is also shorter; when the minimum stiffening is not met,the specimens exhibit the same failure mode as concrete-filled square steel tubular columns. Based on the test results,the minimum stiffening requirement was suggested and a method was proposed to calculate load carrying capacity under axial load for concrete-filled square steel tubular columns stiffened with PBL,which is agreed with experiments.