Research On Mechanical Behavior Of Concrete-Filled Square Steel Tube Middle-Long Columns With Inner I-Shaped CFRP Under Eccentric Loading

Concrete-filled square steel tube column with inner I-shaped CFRP profiles is a new type composite component.This new type of composite column is the CFST column with inner I-shaped CFRP profiles,the column can has bigger bearing capacity,better ductility.In the past,the behavior of CFST columns have been the subject of many investigations.Also analysis of this new type composite columns is involved little.In this paper,a comprehensive analysis was presented on the mechanical behavior of concrete-filled square steel tube columns with inner I-shaped CFRP profiles under eccentric loading by the test and finite element analysis methods.A total of 18 specimens were tested.The main parameters were eccentric ratio and slenderness ratio.The test used static loading,then obverved the failure,N-um curves,N-ε curves and the influence of experimental parameters on specimens and study the mechanism of the specimens under eccentric loading.ABAQUS was used to do the finite element analysis,then adjusted the constitutive modes,boundary conditions and meshes to make the simulation results fit well with the test results on failure mode and N-um curves.Based on the deep study of the test and simulation,mechanic proformance of the specimens were analysised.Moreover,the influence of bearing capacity,stiffness by different parameters is disscuessed.Examined the calculation formula of bearing capacity by different methods.Which include GB 50936(2014),Concrete-filled steel tubular structures-theory and practice(2016)and AISC-LRFD(1999).Then derived a formula to calculate the bearing capacity for the concrete-filled square steel tube columns with inner I-shaped CFRP profiles under eccentric loading.The results showed that all specimens were global buckling failure and also had good ductility during failure process.The load and midheight deflection curve of the column could be divided into 3 stages,elastic stage,elastic-plastic stage,decline stage.Putting the CFRP in CFST can improve bearing capcity,especially the specimens with small slenderness ratio and eccentric ratio.The results showed the eccentric ratio and slenderness ratio had obvious efffects on the mechanical behavior.With the increase of eccentric ratio and slenderness ratio,the bearing capacity decreased quickly.With the increase of concrete strength,yield strength and steel ratio,the bearing capacity increased,but the elastic stiffness of the spencimens almost constant.The calculations of GB 50936(2014)and Concrete-filled steel tubular structures-theory and practice(2016)were more accurate than AISC-LRFD(1999).AISC-LRFD(1999)was quite conservative for predicing the ultimate loads of the eccentriclly loaded lolumns.Based on the different formulas,a more concise and accurate formulas is put forward.It is suggested that the new formula could be used to calculate the bearing capacity of the eccentriclly loaded lolumns.