Experimental Study On Axial Compressive Behavior Of Recycled Aggregate Concrete Filled Square Steel Tubular Short Columns With Inner FRP Tube

The recycled aggregate concrete filled square steel tubular columns with inner FRP tube is a new type of composite column component.The component can give full play to the advantages of steel tubular,FRP tube and recycled aggregate concrete.It is a structural component with engineering application prospect.In this paper,16 short columns(including 10 recycled aggregate concrete filled square steel tubular columns with inner FRP tube and 6 recycled aggregate concrete filled square steel tubular columns)were tested under axial compression with the main parameters of replacement rate of recycled aggregate,wall thickness of steel tubular,thickness of inner FRP tube and material type of inner FRP tube.At the same time,as a comparison and reference,5 FRP confined recycled aggregate concrete short columns and 3 recycled aggregate concrete short columns were tested under axial compression.The specific research work and main research results are as follows:(1)Based on the analysis of the axial load-strain curve of the recycled aggregate concrete filled square steel tubular columns with inner FRP tube,it is found that the typical axial compression process can be divided into five stages: elastic stage,elastic-plastic stage,sandwich concrete failure stage,core concrete strengthening stage,FRP fracture(column bearing capacity loss)stage.In the process of compression,the specimen experiences two peak values of bearing capacity,that is,the bearing capacity decreases slowly after reaching the first peak value,and then rises again to the second peak value.(2)By comparing the axial compression behavior of recycled aggregate concrete filled square steel tubular columns with inner FRP tube with different wall thickness of steel tubular,it is found that the short columns with smaller wall thickness of steel tubular have local buckling earlier,which leads to smaller ultimate bearing capacity.(3)By comparing the axial compression behavior of recycled aggregate concrete filled square steel tubular columns with inner CFRP tube with different thickness of inner FRP tube,it is found that the greater the thickness of the CFRP tube is,the higher the later bearing capacity of the column is.At the same time,even if the CFRP tube breaks,it will not cause the instantaneous decrease of the bearing capacity of the column,that is,the column will not have brittle failure.(4)By comparing the axial compression behavior of recycled aggregate concrete filled square steel tubular columns with inner CFRP tube with different replacement rate of recycled aggregate,it is found that with the increase of recycled aggregate replacement rate,the ultimate bearing capacity of short columns with larger wall thickness of steel tubular decreases gradually,but the decrease range is limited.(5)By comparing the axial compression behavior of recycled aggregate concrete filled square steel tubular columns with inner FRP tube with different material type of FRP,it is found that the recycled aggregate concrete filled square steel tubular columns with inner CFRP tube has higher later bearing capacity than the recycled aggregate concrete filled square steel tubular columns with inner PET tube,but its ductility is far less than the recycled aggregate concrete filled square steel tubular columns with inner PET tube.(6)Based on the experimental study,the constitutive model of recycled aggregate concrete filled square steel tubular columns with inner CFRP tube is established,and the calculation formula of bearing capacity of recycled aggregate concrete filled square steel tubular columns with inner CFRP tube is proposed.The calculation results of the bearing capacity of the columns has a high degree of matching with the test results.The research results of this paper can provide a reference for the design of recycled aggregate concrete filled square steel tubular columns with inner FRP tube,and it is expected to promote the application of the new composite columns in engineering practice,and open up a new field of recycled concrete application.