Theoretical Analysis And Experimental Study On The Behavior Of L-Shaped Columns Comprising Square Concrete-Filled Steel Tubes Under Eccentric Compression

In order to solve the problem of the exposed pillars in the house,the concept of the special-shaped column is proposed in the engineering application.Based on the original concrete-filled tubular(CFST)column form,paper proposes a new component form: columns comprising square concrete-filled steel tubes(CSCFST column).The plurality of square steel tubes of the column are welded to form a special-shaped column,so the force performance of the member is different from that of the CFST column.So the mechanical performance of the CSCFST columns are different from that of the LCSCFST columns.In order to reveal the mechanical performance of LCSCFST column under eccentric compression and promote the application of the LCSCFST columns in engineering,this paper studied the mechanical performance of LCSCFST columns under eccentric compression through theoretical and experimental research.According to the orthogonal analysis table,nine test specimens were produced for testing.The influence of slenderness ratio,steel tube thickness,eccentricity and the direction of bending moment on the eccentric compression bearing capacity of the LCSCFST columns were studied.The finite element analysis model of LCSCFST columns is established based on the experimental conditions.The results of finite element model analysis are basically consistent with the experimental conditions.Combining the finite element model with the experimental data,the interaction between the influencing factors of the LCSCFST columns were analyzed.Based on the results of parameter analysis,the uniaxial eccentric compression bearing capacity formula and the bidirectional eccentric compression bearing capacity formula of the LCSCFST columns are obtained by regression analysis of the calculation results of a large number of finite element models.By the envelope of finite element curve,simplified formulas for calculating the eccentric compression of the LCSCFST columns are obtained.Research shows: The order of influence factors is eccentricity,steel tube thickness,slenderness ratio and bending moment direction.During the whole test process: the specimens showed good stability,and no out-of-plane instability occurred.Before the ultimate load was reached,the change of the section strain along the height in the test piece basically conforms to the flat section assumption.The connecting weld among the steel tubes did not crack;the steel tubes and the concrete showed well collaborative performance.The finite element model established in the paper has good precision and reliability and can be used for the analysis of LCSCFST columns.And it can be used in the simulation of mechanical performance of LCSCFST columns under eccentric compression.In the range of test parameters,when the ultimate load is reached,the torsional deformation of the specimens are small,and the bending instability occurs before the torsional instability.And torsion constraints have little effect on the bearing capacity of the LCSCFST columns under eccentric loading.The results show that the slenderness ratio,steel tube thickness,eccentricity and the direction of bending moment have significant influence on the eccentric compression bearing capacity of the LCSCFST columns The interaction between the slenderness ratio and steel tube thickness,eccentricity and steel tube thickness can be ignored.And the interaction between the slenderness ratio and the eccentricity cannot be ignored.Comparing the formula calculation results with the finite element results,it is found that the formula calculation results are in good agreement with the finite element analysis results.Test data points are outside the simplified calculation formula curve.It's safer to calculate the eccentric compression bearing capacity of the LCSCFST columns by simplified formula.