Performance Of Circular Concrete Filled Double Skins Steel Tube (CFDST) Enclosed With Reinforced Concrete (RC) Laminated Long Columns Under Axial Compression

Concrete filled double skins steel tube(CFDST)enclosed with reinforced concrete(RC)laminated column is a new type of composite member developed on the basis of CFDST column and concrete filled steel tube(CFST)enclosed with RC laminated column,which has the characteristics of high bearing capacity and good ductility.The research of CFDST enclosed with RC laminated column can supplement and perfect the steel tube concrete composite structure and optimize the shortcomings of traditional composite structure.At present,there is no research report on circular CFDST enclosed with RC laminated column.Based on this,this paper studies the axial compressive behavior of concrete-filled circular hollow sandwich steel tubular composite long columns.The details are as follows:(1)The reasonable material constitutive relation and the boundary conditions of the model are selected,and the FEA model of the circular CFDST enclosed with RC laminated long column is established by using the finite element software ABAQUS.The applicability of the model is verified by the axial compression tests of the circular CFDST long columns and the circular hollow CFST enclosed with RC laminated long columns.The results show that the average value of the ratio of finite element method to test result of the axial bearing capacity of the circular CFDST long columns is 0.994,the average value of the ratio of finite element method to test result of the axial bearing capacity of the circular hollow CFST enclosed with RC laminated long columns is 0.919.(2)Based on the parameters of hollow section ratio,CFDST ratio,slenderness ratio,steel strength,concrete strength and steel tube thickness,26 FEA models are designed to analyze the axial compression mechanical properties of circular CFDST enclosed with RC laminated long columns.The load deflection curve of each specimen under axial compression is obtained,and the stress distribution nephogram is extracted.The influence of the parameters in this paper on the mechanical performance of circular CFDST enclosed with RC laminated long columns is analyzed,and the strength coefficient and deformation coefficient of each specimen are calculated.With the increase of slenderness ratio from 30 to 60,the ultimate bearing capacity decreases by 7.6% ～ 16.8%;with the increase of hollow section ratio from0.25 to 0.55,the ultimate bearing capacity decreases by 1.5% ～ 14.0%;with the increase of CFDST ratio from 0.5 to 0.7,the ultimate bearing capacity increases by 4.5% ～ 8.4%.(3)On the basis of FEA and previous related studies,considering the influence of slenderness ratio,the appropriate calculation formula of stability coefficient is determined,and the calculation formula of axial compression bearing capacity of circular CFDST enclosed with RC laminated long columns considering stability coefficient is proposed,the formula is verified by combining with the calculation results of finite element.The deviation between the finite element and the formula is basically within 10%,the average value of the ratio is 0.934 and the variance of the average value is 0.029.