Study On Axial Compression Performance Of Precast Circular Semi-continuous Concrete Filled Steel Tubular Columns

Under the background of"double carbon",the"14th Five-Year Plan"for the Development of Construction Industry clearly proposes to vigorously develop assembled buildings,which means that assembled buildings will be the future development trend of the construction industry.Compared with reinforced concrete structure,steel tube concrete structure has higher bearing capacity and ductility,and assembled steel tube concrete structure will be an important development direction of future assembled structure.However,the assembled steel tube concrete structure needs to solve the problem of reliable connection between beam-column and column-column.To address the above problems,this group proposes a precast circular semi-continuous concrete filled steel tubular（PCSCFST）column-the column consists of upper and lower steel tube concrete columns assembled by the outer steel tube and high strength bolts.Therefore,this paper adopts a combination of experimental research,finite element numerical simulation and theoretical analysis to investigate the axial compression performance of the PCSCFST column,and the main research contents and main findings are as follows:（1）17 specimens（4 continuous type steel tube concrete columns,12PCSCFST columns with bolted connections,and 1 PCSCFST column with a combination of bolts and welds）were tested in axial compression,and the damage modes,load-displacement curves and strains of the specimens were analyzed.The results show that:the PCSCFST column has stronger stiffness and ultimate bearing capacity than the continuous steel tube concrete column;the stiffness and ultimate bearing capacity of the specimen are significantly improved by increasing the thickness of the upper and lower steel tubes and the yield strength of the upper and lower steel tubes;the ultimate bearing capacity of the specimen is reduced by about 6.5%by increasing the bolt diameter from 12 mm to 18 mm,but the falling section of the load-displacement curve is more The load-displacement curve is smoother;（2）The finite element model was established by ABAQUS,and the influence of parameters such as steel tube thickness and yield strength,specimen length/slenderness ratio on contact stress,longitudinal stress and load-displacement curve was analyzed;the influence of parameters such as upper and lower steel tube yield strength and steel tube thickness,concrete strength,bolt diameter and number on load-displacement curve was further analyzed.The results show that:the thickness of the steel tube increases,the contact stress between the steel tube and the outer steel tube decreases,while the contact stress between the steel tube and the core concrete increases;the closer the area covered by the outer steel tube is to the bolt,the greater the longitudinal stress,showing a similar parabolic form of growth and decay,with the maximum stress near the bolt;the yield strength of the upper and lower steel tube(f_y1)increases with the thickness（t₁）,the stiffness of the specimen and the ultimate bearing capacity is strengthened,f_y1 from 235Mpa to 690Mpa,the bearing capacity increased by about 150%,t₁ from 3.5mm to 7mm,the ultimate bearing capacity increased by about 100%;the length of the specimen（L₄）increases,the ultimate bearing capacity and stiffness shows a gradual weakening trend;when the length of the specimen exceeds 840mm（λ=24）,the load-displacement curve appears decreasing section.（3）Based on the axial compression load capacity calculation formula and theoretical analysis in the literature,the calculation formula of axial compression load capacity of PCSCFST column is proposed and compared with the test and finite element results.The results show that:the calculation error of the ultimate bearing capacity of the PCSCFST column by Lai and Ho model,Alrabeh model,and the formula for calculating the bearing capacity in the technical specification of steel tube concrete structure is large,and the average error reaches about 14%;the average ratio of the ultimate bearing capacity of the finite element simulation and the calculation result of the proposed bearing capacity formula is 1.006,and the standard deviation is 0.0389,the accuracy and applicability of the formula are high.