Analytical Study Of Circular Concrete-filled Steel Tube Stub Columns Under Axial Compression

In current practice, concrete-filled steel tubular (CFT) column has been widelyused in building and bridge due to its effective interactions between filled-in-concreteand steel tube, which draw the strong points of each other to offset their ownweaknesses. Additionally, CFT columns can be utilized for retrofitting purpose forresisting earthquake and other accidental loads.Currently, only a few confined constitutive modes of concrete are available fornumerical analysis and their limitations vary widely due to special nonlinear behaviorof concrete. Among most of them, the confining pressure must be assumedpreliminarily rather than being solved directly with the every increasing step of theaxial strain. Given this, Xiao’s concrete constitutive mode under triaxial compressionis adopted in this paper. Using octahedral stress-strain expression, Xiao’s concretemode can be easily combined with plastic theory to conduct the whole processanalysis of CFT column under compression whilst other proposed models needcomparatively fussy solutions related to their own forms of concrete constitutivemodes.This paper describes a numerical method based on confined concrete constitutivemode of Xiao (1989) to analyze the concrete-filled steel tubular (CFT) stub columnswith length-to-diameter ratio of2.0–3.0. Compared with other methods, a simpleranalytical approach can be derived due to Xiao’s concrete constitutive model usingthe octahedral stress-strain relationship based on experimental tests. In the meantime,a simplified constitutive mode of steel, including elastic, plastic, hardening andsecondary plastic stages, is adopted. Comparing with analytical studies by Choi andXiao (2010)[67]without considering strain hardening of the steel tube, eight morelateral conditions of interaction between steel and filled-in-concrete were added toanalytical model of CFT columns system derived by Choi (2007)[73]. To verify theaccuracy of this method, this paper compares the results calculated by this analyticalmodel with previous experimental tests. The predicted curves can accurately catch thebehavior of the CFT columns with obvious hardening effect. Such approach can befurther extended to analyze the confined concrete-filled steel tubes (CCFT). Furtherresearch is on the way to fulfill such extension.