Experimental Study And Theoretical Analysis On Mechanical Performance Of Recycled Aggregate Self-Compacting Concrete-Filled Circular Steel Tubular Columns Under Axial Compressive Loading

Concrete-filled steel tube has been widely used because of its high bearing capacity,good plasticity and toughness.Recycled aggregate concrete(RAC)is produced by waste concrete.The development and application of RAC can reduce the consumption of natural aggregate and save natural resources.Self-compacting concrete can consolidate under its own gravity without vibrations.The recycled aggregate self-compacting concrete-filled steel tube(RASCST)is manufactured by filling the recycled aggregate self-compacting concrete in the steel tube.RASCST can make the performance of both steel and concrete more fully,promote the recycling of waste concrete,and reduce the cost of the project.Therefore,the experimental study and theoretical analysis on mechanical performance of RASCST columns under axial compressive loading is developed.The experimental study on mechanical performance of recycled aggregate self-compacting concrete columns is presented,the effects of water-cement ratio and replacement ratio of recycled coarse aggregate on mechanical performance of recycled aggregate self-compacting concrete columns are analyzed.The test results show that the failure modes of the specimens are similar to the normal concrete.The crack of recycled aggregate self-compacting concrete columns,however,appears earlier and develops quicker than normal concrete.As the water-cement ratio increases,the ultimate bearing capacity,the peak strain,the elasticity modulus of the specimen all decrease,the Poisson’s ratio firstly increases and then decreases.As the replacement ratio of recycled coarse aggregate increases,the ultimate bearing capacity,the elasticity modulus,the Poisson’s ratio of the specimen all decrease,but the peak strain increases.Based on recycled aggregate self-compacting concrete experimental study,the equations of ultimate bearing capacity,peak strain,elasticity modulus,Poisson’s ratio of recycled aggregate self-compacting concrete are proposed,the stress-strain model on recycled aggregate self-compacting concrete is established.The calculation results of the model are in good agreement with the experimental results.Based on the model,the MATLAB program is generated,the effects of water-cement ratio,replacement ratio of recycled coarse aggregate and sand ratio on the stress-strain relationship are analyzed.The experimental study on mechanical performance of RASCST columns under axial compressive loading is carried out,the effects of diameter-thickness ratio,core concrete strength,aspect ratio and replacement ratio of recycled coarse aggregate on the failure mode,bearing capacity,deformation,stiffness and stress-strain relationship of RASCST column are analyzed.The test results show that the failure pattern of short columns is compression bucking failure,and the failure pattern of mid-height columns is compression bending bucking failure.The ultimate bearing capacity decreases with the increase of diameter-thickness ratio,aspect ratio and replacement ratio of recycled coarse aggregate,and increasing with the increase of core concrete strength.The ultimate strain decreases with the increase of diameter-thickness ratio,aspect ratio and replacement ratio of recycled coarse aggregate,and increasing with the increase of core concrete strength.The speed of stiffness degradation increases with the increase of diameter-thickness ratio,aspect ratio and replacement ratio of recycled coarse aggregate,and decreasing with the increase of core concrete strength.The elastic stage of stress-strain curve decreases with the increase of diameter-thickness ratio,aspect ratio and replacement ratio of recycled coarse aggregate,and increasing with the increase of core concrete strength.Based on the experimental study,considering the effects of replacement ratio of recycled coarse aggregate,core concrete strength,diameter-thickness ratio and aspect ratio,the calculation formulas of bearing capacity and deformation of RASCST columns under axial compressive loading are deduced,and the related simplified calculation formulas are also put forward.Based on the reasonable stress-strain model of materials,the MATLAB program is compiled to simulate the full-range analysis of RASCST columns under axial compressive loading.The effects of steel yield strength,aspect ratio,core concrete strength and replacement ratio of recycled coarse aggregate on RASCST columns under axial compressive loading are studied,and the stress-strain model of RASCST columns under axial compressive loading is established.Based on the reasonable stress-strain model of material,selecting element model,determining the boundary conditions and loading methods,dividing the mesh,defining convergence criteria,using finite element analysis software ABAQUS,the finite element analysis model of RASCST columns under axial compressive loading is established.Based on the finite element analysis model,the effects of steel yield strength,aspect ratio,core concrete strength and replacement ratio of recycled coarse aggregate on the stress-strain relationship of RASCST columns under axial compressive loading are analyzed,and the working mechanism of RASCST columns under axial compressive loading is revealed.