| The recycled concrete-filled circular steel tube column with FRP tube is a new type of composite structural component,which is a kind of structural component with engineering application prospect.In this paper,10 recycled concrete-filled circular steel tubular columns with FRP tubes and 6 ordinary recycled concrete-filled circular steel tubular columns were tested under axial compression with the main parameters of concrete recycled aggregate substitution rate,steel tube wall thickness,FRP inner tube thickness and FRP inner tube type.At the same time,as a reference,10 FRP confined recycled concrete columns and 6 recycled concrete columns were tested.The main work and research results are as follows:(1)The failure mechanism of the recycled concrete-filled circular steel tube composite column with FRP tube is expounded based on the axial compression test of the recycled concrete-filled circular steel tube column with FRP tube.With the increase of load,the hoop strain of FRP inner pipe of composite column reaches the ultimate hoop strain of FRP confined concrete.At this time,due to the constraint of steel tubular and sandwich concrete on FRP tube,FRP pipe is not completely broken,and the bearing capacity of composite column continues to rise.With the crushing of sandwich concrete,the local buckling of steel tube appears and increases continuously,and the restraint effect of steel tube and sandwich concrete decreases,leading to the local fracture of FRP tube and the decrease of bearing capacity of composite column.With the tearing of the steel tube,the concrete filled inside is crushed,and the specimen is finally destroyed.(2)The influence of the test parameters,such as the replacement ratio of recycled aggregate,the thickness of FRP pipe and the material type of FRP tube,on the axial compression performance of the recycled concrete filled circular steel tubular column with FRP tube was studied.The results show that with the increase of the replacement rate of recycled aggregate,the ultimate bearing capacity and the peak hoop strain of the recycled concrete filled steel tubular columns with FRP tubes decrease to some extent.With the increase of FRP tube thickness,the ultimate bearing capacity of recycled concrete filled steel tubular columns with FRP tube increases.In addition,it is found that the peak axial strain of the composite column with pet-frp inner tube is larger than that of the composite column with CFRP inner tube,while its peak hoop strain and ultimate bearing capacity are smaller than that of the composite column with CFRP inner tube.(3)Based on the experimental study of FRP confined recycled concrete columns and circular steel tubular recycled concrete columns with FRP tubes,the development of axial and hoop strains of FRP tubes in composite columns under axial compression is analyzed.The results show that the axial peak strain of FRP in composite columns is larger than that of FRP confined recycled concrete columns.The hoop peak strain of FRP inner tube of composite column is smaller than that of FRP confined recycled concrete column.Among them,when PET-FRP is used in the composite column,the circumferential strain of the inner tube develops most slowly.In addition,the greater the thickness of steel tube,the slower the hoop strain development of FRP inner tube.(4)The influence of FRP inner tube on the ultimate bearing capacity of recycled concrete filled circular steel tube columns with FRP inner tube was studied by comparing the test data of recycled concrete filled circular steel tube columns with FRP inner tube and that of ordinary recycled concrete filled circular steel tube columns.The results show that the ultimate bearing capacity of the composite columns with built-in CFRP tube and PET-FRP tube is 24% and 14% higher than that of the corresponding recycled concrete filled steel tubular columns.At the same time,FRP inner tube can improve the ultimate bearing capacity of composite columns with small wall thickness.(5)The ductility of recycled concrete-filled circular steel tubular columns with FRP tube was evaluated.The results show that the ductility of recycled concrete filled circular steel tubular columns with FRP tubes is better than that of ordinary recycled concrete filled steel tubular columns.The ductility of composite columns with small thickness of steel tube is improved by FRP inner tube.At the same time,the type of FRP inner tube material has great influence on the ductility of composite columns.The ductility of composite columns with built-in CFRP tube and PET-FRP tube is 190% and771% higher than that of the corresponding recycled concrete-filled steel tube.WhenPET-FRP inner tube is used,the ductility of composite column is the best,while the thickness of FRP tube has little effect on the ductility,which can be ignored.(6)The research results of this paper can provide reference for the design of recycled concrete-filled circular steel tubular columns with FRP tube,and it is expected to promote the application of the new composite columns in engineering practice and open up new areas of recycled concrete application. |
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