Experimental Study And Theoretical Analysis On Mechanical Behavior Of Recycled Self-Compacting Concrete Filled Circular Steel Tubular Columns Under Eccentric Compression

As a kind of main composite structure,concrete filled steel tube has the advantages of high bearing capacity,low steel consumption,good ductility and fire resistance,convenient construction and low cost.In the process of urbanization,natural aggregates need to be largely exploited,at the same time,a lot of old building demolition and renovation project will produce a large number of abandoned concrete,which lead to the destruction of the environment and the waste of resources,however,applying the recycled concrete in the field of structural engineering can realize the recycling of waste concrete,in the existing study,we can see that the recycled concrete will meet the requirements of the material function and structure using.But the compacting effect of concrete in steel tube is not good,prone to produce some defects,such as honeycomb pipe,they not only influence the strength of concrete core but also lead to the role of steel tube on the core concrete which is not effectively play,and it is easy to destroy the structure when the specimen is too long.Self-compacting concrete can achieve good self-compacting effect in its own gravity or slight vibration,it not only ensures the density of the core concrete,but also simplifies the construction process,shorten the construction period and significantly reduce the project cost.Therefore,in this paper,the experimental study and theoretical analysis on mechanical behavior of recycled self-compacting concrete filled circular steel tubular columns under eccentric compression are carried out.The experimental study of recycled self-compacting concrete filled circular steel tubular columns under eccentric compression is conducted,the replacement ratio of recycled coarse aggregate,concrete strength,slenderness ratio and eccentricity influence on specimen such as bearing capacity,stiffness,ductility,strain,deflection and curvature are considered.The results show that the recycled self-compacting concrete filled circular steel tubular short columns under eccentric compression is buckling and destroying,which belongs to the failure of strength,the recycled self-compacting concrete filled circular steel tubular medium long columns under eccentric compression is damaged due to loss of stability and belongs to the elastic-plastic failure.With the increase of the replacement ratio of recycled coarse aggregate,the bearing capacity of the specimen decreases,the ductility coefficient increases,and the stiffness degradation slows down,the strain growth rate accelerates,and the deflection and curvature growth rate become slower.With the increase of concrete strength grade,the bearing capacity of specimen increases,the ductility coefficient increases,and the stiffness degradation slows down,the strain growth rate slows down,and the deflection and curvature growth rate become slower.With the increase of the length to diameter ratio and the eccentricity,the bearing capacity of the specimen decreases obviously,the ductility coefficient of the specimen decreases,and the stiffness degradation speed increases,the strain,the deflection and curvature growth rate accelerates.Based on the experimental syudy,Considering the recycled coarse aggregate replacement ratio influence coefficient,the equivalent confining force interaction between steel tube and recycled self-compacting concrete is put forward.According to the limit equilibrium method and the crushing principle,the bearing capacity calculation formula of short columns under eccentric compression is deduced.According to the axial force-moment equation,considering the influence of recycled coarse aggregate replacement ratio and length diameter ratio on the bearing capacity of specimen,the bearing capacity calculation formula of medium long columns under eccentric compression is presented.Considering the influence of recycled coarse aggregate replacement ratio and ratio of length to diameter,the stiffness calculation model is established by the curvature method,the formula for calculating the section stiffness of recycled self-compacting concrete filled circular steel tubular columns under eccentric compression is presented.Based on the layered method,using MATLAB software to analysis the whole process of recycled self-compacting concrete filled circular steel tubular columns under eccentric compression,considering the influence of yield strength of steel,steel ratio,concrete strength and the slenderness ratio on bearing mechanism of the specimen.In order to simplify the model,using the two stage equation to represent the test piece elastic stage and plastic deformation stage,establish stress-strain relationship model,moment-curvature relationship model and load-deflection relationship model of specimens,consider the influence of recycled coarse aggregate replacement rate,slenderness ratio,eccentricity and the hoop coefficient on the relationship model,the calculated results of the model are in good agreement with the experimental results.Reasonably selecting the stress-strain relationship of steel and recycled self-compacting concrete,using finite element analysis software ABAQUS,defining the contact between the entities and constraints,creating the loads and boundary conditions,setting the analysis step,determining the element type and mesh regeneration,the finite element analysis model of recycled self-compacting concrete filled circular steel tubular columns under eccentric compression is established.Analyze the influence of yield strength of steel,steel ratio and concrete strength on the relationship model,the calculated results of the model are in good agreement with the experimental results,the working mechanism of steel tube and recycled self-compacting concrete under eccentric compressive loading is revealed.