Research On Mechanical Behavior Of Concrete-Filled Square Steel Tube Short Columns With Inner I-Shaped

Concrete-filled square steel tubes with inner I-shaped CFRP is a new composite structure which was formed by placing the I-shaped CFRP reinforced material as core material in Square concrete filled steel tubes.This kind of composite structure can significantly improve the bearing capacity and retain the ductility of concrete-filled square steel tubes.At the same time,I-shaped CFRP placed in concrete-filled square steel tubes can further reduce the section size of members.Distinguishing the strong axis from the weak axis reduces the waste of materials to a certain extent.In this paper,seven concrete-filled square steel tubes with inner I-shaped CFRP short columns under bi-axial eccentric are tested.By the experiments,we got the load-lateral displacement curves,the load-longitudinal strain curves,and by the data processing,we got the load-stress curves and the load-transverse longitudinal strain ratio curves.Then,on the basis of adopting reasonable constitutive relation,finite element analysis of this kind of members were carried out by using finite element analysis software ABAQUS.The results of finite element analysis are basically in agreement with the experimental,it is fully proved that the finite element analysis formula adopted in this paper is reliable.Expanding research parameters for simulation,the effects of parameters eccentricity,steel ratio,yield strength of steel and compressive strength of concrete on the mechanical properties of components are studied.We also studied the interaction among the components in the specimen.We studied the variation of strain and stress at the different height of each section during the whole process of loading.Changing parameters to make P/Pu-M/Mu curve of this type of members.Finally,through data fitting and numerical calculation,the proposed formulas for calculating the bearing capacity of concrete-filled square steel tubes short columns with inner I-shaped CFRP bi-axial eccentric were given.The research shows that the ultimate bearing capacity decreases with the increase of eccentricity,increases with the increase of steel content,yield strength of steel and compressive strength of concrete.The confinement of steel tube corner to concrete is obviously greater than that of steel tube plate to concrete.The effect at the interface area between profile flange and web on concrete is more obvious,followed by web area,the weakest at the outside of flange.It can also be found that the compressive strength of concrete,steel yield strength and steel ratio has little effect on the P/PuM/Mu curves.The equilibrium point moves outward with the increase of concrete compressive strength.The equilibrium point moves inward with the increase of steel yield strength and steel radio.The experimental results are compared with the calculated results by using the proposed formula.The proposed bearing capacity formula can effectively predict the bearing capacity of concrete-filled square steel tubes with inner I-shaped CFRP short columns bi-axial eccentric.