Study On The Axial Compression Behavior Of Recycled Concrete-filled Square CFRP-steel Tube Columns

With the further development of the construction industry,the forms of building structures are becoming more and more diverse.With the rise of high-rise and super high-rise buildings,the traditional structure forms have slowly failed to meet the requirements of the building industry.We urgently need to find a new structure.Form to further improve the performance of traditional steel-concrete structures.At the same time,the development of the building will necessitate the dismantling of some old buildings,which will generate a lot of construction waste.In order to comprehensively solve these two problems,this paper proposes a new structural form: square CFRP-reinforced concrete steel tube column.The performance of the structure is studied.In this paper,the CFRP-reinforced concrete column of the steel tube is tested from two aspects: short column and long column.First,in the preparation stage of the experiment,the mix ratio of recycled concrete was calculated and analyzed,and then the properties of CFRP composite materials,steel pipes,recycled concrete and other materials were analyzed.For short columns,9 test pieces were made for axial compression test.The factors considered are: the number of layers wrapped by CFRP composite material,the replacement rate of recycled concrete,and the wrapping method of CFRP composite material.Through the analysis of the test phenomenon of short column failure,it was found that the form of short column failure is basically the same,that is,the bulge occurs in the middle of the specimen first,then the CFRP composite material breaks,and finally the specimen fails.By comparing and analyzing the load-displacement curves of these 9 specimens,it is found that the load-displacement curve of short columns is mainly divided into elastic stage,elastoplastic stage,and plastic stage;for short columns with a replacement rate of recycled concrete of50% and 100%,The CFRP package of the first layer can increase the bearing capacity by about 30%,and the CFRP package of the second layer can increase the bearing capacity of about 30%;the short column of the CFRP package of the first layer,the replacement rate of recycled concrete increases from 0 to 50% to make the bearing capacity reduced by about30%,when the replacement rate reached 100%,the bearing capacity was reduced by about40%;the bearing capacity of the fully wrapped specimen was about 2% higher than the strip wrapped specimen.For long columns,10 test pieces were made for axial compression test.The factors to be considered are: slenderness ratio of test piece,number of layers wrapped by CFRP composite material,replacement rate of recycled concrete,and wrapping method of CFRP composite material.Through the analysis of the test phenomenon of long column failure,it is found that the form of long column failure is basically the same.Both the specimens buckled first,then the fracture sound of the CFRP composite material can be heard,the CFRP is seen to be broken,and finally the specimen is destroyed and deformed is too big.By comparing and analyzing the load-displacement curves of these 10 specimens,it is found that the load-displacement curve of long columns is mainly divided into elastic stage,elastoplastic stage,strengthening stage,and plastic stage;when the slenderness ratio increases from 23.1 to27.7,the column bearing capacity decreases slightly,about 2%,when the slenderness ratio increases from 23.1 to 32.3,the bearing capacity of the column decreases by about 13%,and when the slenderness ratio increases from 11.5 to 27.7,the bearing capacity of the column decreases about 40%;for long columns with a replacement rate of recycled concrete of 100%,adding 1 layer of CFRP wrapping can increase the bearing capacity by about 10%,and adding2 layers of CFRP wrapping can increase the bearing capacity by about 20%;for 1 layer of CFRP for wrapped long columns,the replacement rate of recycled concrete increases from 0to 50%,which reduces the bearing capacity by about 10%.When the replacement rate reaches100%,the bearing capacity decreases by about 20%;CFRP fully-wrapped long columns are compared with three strips.The bearing capacity of the long column is about 10% higher,but it is about 4% higher than that of the four-bar wrapped long column.After the completion of the test analysis,the calculation and analysis of the bearing capacity of the square CFRP-reinforced concrete column was carried out.The calculation formula of the bearing capacity of the structural form was summarized and deduced.The calculation results were in good agreement with the test results and provided a reference for subsequent relevant research in accordance with.