Experimental Study And Finite Element Analysis On Recycled Aggregate Concrete-filled Square Steel Tube Long Columns Under Axial Compression

On the basis of previous studies,the performance of recycled concrete can be concluded that the properties of recycled concrete are weaker than those of ordinary concrete.This must be a hindrance to the application of recycled concrete.After that,scholars were inspired by the structural form of CFST.Similar structure was taken into account for the utilization of recycled concrete,that's to say,the recycled concrete was poured into the steel tube to form a composite structure--steel tube recycled concrete.The interaction of the two materials can not only increase the bearing capacity of the specimens,but also solve the problems of the mechanical properties and durability of recycled concrete.It provides new ideas and ways for the recycling of waste concrete and the development of recycled concrete.There is not much research on the axial compression performance of the long column of square steel tube recycled concrete at home and abroad.Most of them are focused on the performance research of short columns of concrete filled steel tube.the axial compression performance of the regenerated concrete long column of the steel tube is deeply and systematically studied in this paper.In this paper,the experimental study on the axial compression performance of 14 long columns of recycled concrete filled square steel tubes is carried out.The main factors considered are the replacement ratio of recycled aggregate,the thickness of the steel tube,the ratio of length and length,the form of support and the additive.The bearing capacity,the axial load displacement curve,the axial load and the lateral deflection curve of the axial load are studied.The influence of the replacement ratio of recycled aggregate,the thickness of the steel tube,the ratio of length and length,the form of support and the additive to the bearing behavior of the axial compression long column of the recycled concrete filled steel tube,and the axial load longitudinal strain curve and the lateral deflection curve of the specimen are also analyzed.On the basis of experimental research,finite element simulation and bearing capacity calculation method are studied.It can be found that all failure characteristics of specimens can be divided into two types,namely,the buckling failure of ends and the whole bending failure of specimens.The substitution ratio of recycled coarse aggregate,steel tube wall thickness,length and length ratio,additive and support form have no obviousinfluence on the failure process and characteristics of the specimen,and the length ratio of the specimen has obvious influence on the failure process and characteristics of the specimen,that is,the local pressure at the end of the steel tube column with smaller length.The deflection of the column with larger length is larger,which is mainly the bending failure of the middle part of the steel tube;the wall thickness of the steel tube has a significant influence on the failure process and the characteristics of the specimen.The upper of the specimens with the smaller wall thickness of the steel tube are more serious,and the middle part of the steel pipe with the thicker wall is larger in the middle,the failure form of the bearing form on the specimen.The influence of additives on the failure modes of specimens is not obvious.In addition,through simulation,it is found that with the increase of replacement rate,the initial axial stiffness and lateral stiffness of specimens decrease,but decrease slightly.The slenderness ratio has a significant effect on the axial stiffness and lateral stiffness of the specimens.With the increase of slenderness ratio,the axial stiffness and lateral stiffness of the specimens are significantly reduced.With the increase of the thickness of the steel tube,the initial axial stiffness and lateral stiffness of the specimens increase,but little influence is observed,but the lateral deformation capacity increases obviously.Finally,the axial compression bearing capacity of recycled aggregate concrete filled square steel tubes(CFST)long columns is calculated by theoretical formulas in China,and the calculated values are in agreement with the experimental values.In order to ensure the safety of the design,the strength of recycled concrete can be reduced to a certain extent when the concrete steel tube regenerated concrete axile compression columns are designed according to the above regulations.