Study On Axial Compression And Seismic Behavior Of L-shaped Concrete Filled Steel Tubular Columns With Different Combinations

The special-shaped column structure solves the problem of protruding column bases inside square columns.Compared to reinforced concrete special-shaped column structures,concrete-filled steel tubular special-shaped column structures have better seismic resistance and better assembly performance,and their application prospects will be broader.For ordinary L-shaped concrete filled steel tubular columns,the external steel pipes are relatively prone to buckling,and the constraint provided by the filled concrete is weak.To improve their mechanical properties,composite L-shaped concrete filled steel tubular columns can be used.However,different combinations of L-shaped concrete-filled steel tubular composite columns during processing and manufacturing can have an impact on the performance of the specimen.Due to the requirements of architectural or structural design,structural columns with different angles between the two legs or different long and short legs may be encountered in practical engineering.Based on the above analysis,this paper studies the axial compression and seismic performance of unequal leg L-shaped concrete filled steel tubular columns under different combinations through experiments and finite element analysis.(1)Eight L-shaped concrete filled steel tubular columns were subjected to axial compression tests to investigate the effects of three variables,namely,different combinations,the ratio of long and short legs,and the angle between the two legs,on the axial compression performance,stiffness,ductility,and bearing capacity of L-shaped concrete filled steel tubular columns.The test results show that the axial compression performance of the F series specimen is the best among the three series specimens;With the increase of the length to length ratio,the bearing capacity and ductility of the specimen will decrease significantly;As the angle between the two legs increases,the bearing capacity of the specimen increases,but the ductility decreases.(2)Based on ABAQUS,a finite element model of L-shaped concrete filled steel tubular columns under axial compression was established and compared with the test results to verify the accuracy of the finite element model.On this basis,the finite element models of various specimens were analyzed,and parametric analysis was conducted using material strength,length to length ratio,angle between the two legs,and different combinations as variables.(3)Using different specifications to predict the test results,it was found that the specifications using the unified theory were more suitable for the test piece in this paper.Therefore,based on parameter analysis,a simplified bearing capacity calculation formula was proposed in this paper,and the results obtained using the formula were in good agreement with the test results.(4)Nine L-shaped concrete filled steel tubular columns were subjected to low cycle cyclic tests to investigate the effects of three variables,namely,different combinations,long and short leg ratios,and loading directions,on the hysteretic behavior,ductility,stiffness,energy dissipation capacity,and bearing capacity of L-shaped concrete filled steel tubular columns.The results show that the bearing capacity of F series specimens is higher than that of the other two series specimens,and the length to length ratio of F series specimens has the greatest impact;The length to length ratio and loading direction have a significant impact on the hysteretic behavior of the specimen.(5)Based on ABAQUS,a finite element model of L-shaped concrete filled steel tubular columns under low cycle reciprocating loading is established.After considering the ductile damage of metal in the model,that can accurately predict the crack location and load displacement curve of steel tubes.Based on the correct finite element model,parametric analysis was conducted using the long short leg ratio,the angle between the two legs,the loading direction,the axial compression ratio,and different combinations as variables.The results show that both the long short leg ratio and the angle between the two legs have a significant impact on the seismic performance of the specimen;When the length ratio and the angle between the two legs are large,the bearing capacity of the specimen will significantly decrease with the change of the loading direction;As the axial compression ratio gradually increases,the bearing capacity and ductility of the specimen gradually decrease.