Mechanical Properties Of Self-compacting Lower Expansion Concrete Filled Rectangular Steel Tube Columns

The superior mechanical properties of ordinary rectangle concrete filled steel tube(CFST)column not only as good as circular CFST column with high strength,good ductility,fatigue resistance,impact resistance,but also has simple node form,flexible architecture layout,good section moment of inertia,good stability,convenient construction and simple fire prevention measures.In addition,the non-equilateral rectangle can provide different bending stiffness in the two main axes to meet the needs of structural optimization.Therefore,the rectangular CFST columns have been applied more and more widely in high-rise buildings at home and abroad due to their unique advantages.With the increasing of self-compacting lower expansion concrete filled rectangle steel tube columns in practical engineering,some problems are gradually reflected such as the difficulty of core concrete vibration.Moreover,the shrinkage and creep of concrete will weaken the restraint effect of steel pipe on concrete,which is not conducive to the improvement of core concrete compressive strength.It is an effective way to improve the working performance of the rectangular steel tube and the core concrete by filling the high performance concrete with self-compacting and lower expansion characteristics to improve the interfacial bonding performance between the steel tube and the concrete.The interface and mechanical properties of self-compacting lower expansion concrete filled rectangle steel tube are studied by the method which is combined with experimental research,finite element simulation and theoretical deduction.A series of experimental studies have been carried out,including the push out test of self-compacting lower expansion concrete filled rectangular steel tube short column,the axial compression test of rectangle CFST short column based on interface damage and the compression-bending test of self-compacting lower expansion concrete filled rectangular steel tube column.On the basis of the experiments,combined with the finite element software ABAQUS,the parameterized analysis and theoretical deduction are carried out,and the following conclusions are obtained:(1)Based on the push-out test,introduce the component load-slip curve,analyze the effect of the expansive agent dosage,the steel section size,steel tube making method,welding interface bonding bolts and concrete strength on the interfacial bond bearing capacity of steel tube and concrete,obtain the development trend of the interfacial bond stress along the length of the component in the short side section and long side direction.(2)Considering the three main influencing factors,the expansive agent dosage,width to thickness ratio D/t and compressive strength of concrete,a formula for calculating the interfacial bearing capacity of self-compacting lower expansion concrete filled square and rectangle steel tube columns is derived based on the experimental data and the existing literature data.On the basis of this,a formula for calculating the interfacial bond slip curve is established in four fold line.(3)Axial compression tests of rectangular steel tube self-compacting lower expansion concrete short columns based on interface damage members were carried out.an effective model for rectangular CFST short columns under axial compression load is established.The effect of interfacial bonding force on the bearing capacity is analyzed.The influence of length width ratio and steel tube forming process on load displacement curve of members is discussed.The calculation accuracy of existing procedures is discussed..(4)The uniaxial and biaxial compression-bending test of self-compacting lower expansion concrete filled rectangle steel tube columns is carried out.Analyse the mechanical properties of components under compression-bending load.A numerical model of self-compacting lower expansion concrete filled rectangle steel tube column is established.The accuracy of calculation for compression-bending capacity and N-M curve of self-compacting lower expansion concrete filled rectangle steel tube columns is discussed.Based on a large number of test data,the calculation methods of bearing capacity in EC4,LRFD99 and CECS159:2004 are compared,and the accuracy and application scope of each specification are discussed.Though the parametric analysis of ordinary CFST columns under compression-bending load by ABAQUS,the influence of eccentricity and slenderness ratio on the compression-bending capacity of CFST columns is obtained.A simplified formula for calculating the compression-bending bearing capacity of CFST columns under small eccentricity is derived in combination with the existing literature test data.