Study On Mechanical Behavior Of Concrete-Filled Square Steel Tube Slender Columns With Inner I-Shaped CFRP Under Axial Compression

In recent years,fiber reinforced plastic has been used more and more widely in the field of civil engineering due to its characteristics of light weight,high strength and designability.The structure formed by the combination of the three materials shows good mechanical properties and application prospects.Concrete-filled square steel tube column with inner I-shaped CFRP is a new type of composite structure that the I-shaped CFRP profile is placed in the concrete-filled steel tube,the mechanical behavior of its column was analyzed.Based on the experimental study,the force performance of concrete filled square steel tube slender column with inner I-shaped CFRP under axial compression is studied by finite element simulation.Taking the slenderness ratio as the main variable parameter,the axial compression tests of ten columns were carried out.The failure modes,the load-deflection curves,the deflection distribution curves,the stress-strain curves and effect of slenderness ratio on the bearing capacity of the specimens were observed and studied.On the basis of this,through the finite element analysis results,the whole process of component force is analyzed to study the stress and deformation of each component in the process of failure.The influence of the change of steel ratio,concrete strength,steel yield strength and slenderness ratio on the mechanical behavior of members was analyzed.Through the combination of data and theory,the limit slenderness ratio was obtained.Finally,based on the formula of bearing capacity of short stub columns,the formula of stability bearing capacity of concrete filled square steel tube composite columns with inner I-shaped CFRP is deduced by empirical coefficient method.The results show that the bearing capacity and ductility of the composite columns have been significantly improved by adding I-shaped CFRP to the concrete filled steel tubes.Component of the force process can be divided into elastic section,elastic plastic section and the descending section of three stages.In the elastic phase,the steel pipe and the core concrete mainly provide the bearing capacity.At this moment,the effect of the CFRP profile is not very obvious.In the elastic-plastic section,due to the plasticity of the concrete and the steel pipe,the bearing capacity does not change much,while the bearing capacity of the CFRP profile continues to rise.In the descending stage,the CFRP profile began to destroy and quit their work,and the bearing capacity of the specimens began to drop significantly.The failure mode of the component is buckling failure.The slenderness ratio has a great influence on the mechanical properties of the column,the bearing capacity of the column decreases obviously with the increase of the slenderness ratio.Increasing the strength of concrete can increase the bearing capacity of the column,but the ductility decreases.Increasing the strength of the steel and increasing the steel ratio can improve the bearing capacity of the column.The presence of I-shaped CFRP profile can improve the bearing capacity and deformation capacity of the column.Based on the stability theory and empirical coefficient method,the steady bearing capacity of the concrete filled square steel tube composite column is in good agreement with the finite element analysis.