| With the development of high-rise and super-high-rise buildings and large-span buildings,the performance requirements of the main load-bearing skeleton of buildings-columns are getting higher and higher.Concrete-filled steel tubular columns are used more and more in modern architectural design because of their high bearing capacity,good seismic performance and convenient construction.It is more and more urgent to study the performance and application theory of concrete filled steel tubular columns.In this paper,SCLC50 high-strength self-compacting lightweight aggregate concrete was prepared with ceramsite as raw material for engineering application.With this concrete as the core concrete filler of concrete filled steel tubular column,high-strength self-compacting lightweight aggregate concrete filled steel tubular column was developed.The bearing capacity of concrete filled steel tubular column under axial compression is studied and the corresponding calculation method is provided.In this paper,by choosing the parameters of stirrup coefficient,slenderness ratio and steel content as variables,the bearing capacity of self-compacting lightweight aggregate concrete filled steel tubular columns under axial compression was analyzed by mutual authentication method of theoretical analysis,experimental research and finite element simulation analysis.The compressive performance of self-compacting ordinary concrete filled steel tubular columns was compared,which provides theoretical and experimental basis for the use of the self-compacting lightweight aggregate concrete filled steel tubular columns.In order to meet the needs of the project,this paper carried out the analysis and research on the bearing capacity of self-compacting lightweight aggregate concrete filled steel tubular columns under axial compression.The main contents include as listed below.1.Mix proportion design of high strength self-compacting lightweight aggregate concrete(SCLC50).First of all,the 900 grade spherical sinterless fly ash ceramsite with relatively simplified basic mechanical properties and technology was selected as aggregate.Secondly,according to"Technical Specification for Application of Self-compacting Concrete"(JGJ/T 283-2012),considering the water cement ratio of mixtures,the volume of ceramsite and the volume of fly ash,the design strength grade was SCLC50self-compacting lightweight aggregate concrete mix ratio.Thirdly,by comparing the working performance of SCLC50 and the strength and apparent density of the test block,the influence weight of each parameter on the mix ratio is determined,and the mix ratio of the self-compacting lightweight aggregate concrete was optimized.Through the above steps,the following results are obtained.(1)The water-binder ratio was the main factor affecting the strength of SCLC50.When the water-binder ratio was 0.30,the standard strength value of concrete was60.8MPa,which meets the strength grade requirements.(2)The apparent density of concrete can be significantly improved by increasing the volume content of ceramsite.When the volume content of ceramsite was 0.38 m~3 and the apparent density of SCLC50 was 1850 kg/m~3,the specific strength was the highest.(3)Active admixture fly ash with its spherical particles and smooth surface can significantly improve the working performance of concrete.When its content was 20%of the total amount of cementitious materials,SCLC50 has the best working performance.2.Experimental study on compression performance of high strength self-compacting lightweight aggregate concrete filled steel tubular columns.The effects of slenderness ratio,steel ratio and hoop coefficient on the compressive behavior and failure mode of self-compacting light aggregate concrete filled steel tubular columns were studied by changing the length,wall thickness and types of concrete parameters.The compressive bearing capacity of columns was also observed.The conclusions are as follows.(1)Under the premise that the core concrete strength grades are SCLC50 and C50respectively,the self-compacting lightweight aggregate concrete-filled steel tubular columns are compared with the self-compacting ordinary concrete-filled steel tubular columns,and the compression failure modes of the two are basically similar.That is to say,when the slenderness ratio of the member is 20,the material strength is mainly broken or sheared,and when the slenderness ratio(λ=25)is large,the bending instability is more obvious.And when the component is damaged,the self-compacting lightweight aggregate concrete-filled steel tubular column has more wrinkles and better deformation performance,but its bearing capacity is smaller than that of self-compacting ordinary concrete-filled steel tubular columns.(2)Among all the research parameters,the most significant influence on the bearing capacity and deformation performance of self-compacting lightweight aggregate concrete-filled steel tubular columns is the strength of core concrete,that is,with the increase of concrete strength,its bearing capacity increases by 35.1%.3.Theoretical study on compression performance of high strength self-compacting lightweight aggregate concrete-filled steel tubular columns.Based on the ultimate equilibrium theory and the unified strength theory of the ultimate bearing capacity of concrete filled steel tubular columns,the bearing capacity of self-compacting concrete filled steel tubular medium-long columns was analyzed and deduced.The theoretical calculation results were compared with the experimental measured values,and the corresponding calculation formulas are determined by fitting the experimental data.4.Simulation analysis of compressive bearing capacity of high strength self-compacting lightweight aggregate Concrete Filled Steel Tubular Columns.On the basis of quasi-static test,the large-scale structural design software ABAQUS was used to carry out the non-linear finite element numerical simulation analysis of the specimens.The following conclusions are drawn.(1)Under the ultimate load,the compressive deformation of all columns was"lantern-shaped",and the maximum compressive deformation occurs in the middle of the column.And with the increase of steel tube wall thickness,the maximum longitudinal compression deformation of the column increases gradually,and the maximum compression deformation could increase by 21.4%.Besides,with the increase of slenderness ratio,the maximum compressive deformation of the column decreased gradually,and the maximum compressive deformation decreased by 45.9%.(2)Longitudinal compressive stress of self-compacting lightweight aggregate concrete filled steel tubular column under ultimate load condition,the maximum increase was 15.7%with the increase of wall thickness of steel tube.And with the increase of slenderness ratio,it decreased by 9.11%.(3)The results of field measurement and finite element analysis showed that the core concrete strength of steel tube column has a greater impact on its bearing capacity,while the thickness of steel tube wall and the length of steel tube have a smaller impact on the bearing capacity of the column.The main reason for this phenomenon is that the strength of core concrete leads to the change of hoop coefficient of columns,which affects the restraint effect of steel tube on core concrete,thus directly affects the bearing capacity of columns. |
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