Study On Axial Compressive Performance Of Recycled Big Aggregate And Self-compacting Concrete Filled Steel Tubular Short Columns

The application of recycled aggregate concrete filled steel tube(RACFST)structure can not only save resources and protect the environment,but also has good economic benefits.The research and application of the structure is a necessary and urgent task.In order to promote the better utilization and development of RACFST structure,the research group has put forward the structure form of "Recycled big aggregate and self-compacting concrete filled steel tube(RBA-SCCFST)" from the aspects of improving the utilization rate of recycled aggregate concrete(RAC),improving the construction speed of concrete filled steel tube(CFST)and ensuring the mechanical properties of the structure.In this paper,the mechanical properties of RBA-SCCFST short columns with steel tube under axial compression are studied,mainly including the experimental study of axial compression,the calculation formula of axial compression ultimate bearing capacity and the simulation study of finite element.The specific research work is as follows:(1)Experimental study on axial compression of RBA-SCCFST short columnsThe waste concrete will be broken into blocks with particle size of 50?130mm as "recycled big aggregate(RBA)" and mixed with self-compacting concrete(SCC)and poured into the steel pipe,nine groups of RBA-SCCFST short columns are designed and manufactured for axial compression test,the parameters of the test are RBA size,RBA strength,SCC strength and steel pipe wall thickness,the influence of these four parameters on the behavior of RBA-SCCFST short columns under axial compression is studied.The failure process and load-strain curve of RBA-SCCFST short columns under axial compression are also studied.The experimental results show that the failure process and phenomenon of RBA-SCCFST short columns are consistent with that of the ordinary CFST under axial compression,and they all show shear failure;The increase of the wall thickness of the steel tube is mainly reflected in the increase of the ductility of the test piece,and the ultimate bearing capacity of the test piece decreases with the increase of the RBA mixing amount,while the strength of the RBA and the SCC decrease with the increase of the RBA mixing amount The increase of strength is positively related to the increase of ultimate bearing capacity.(2)Study on the formula of bearing capacity of RBA-SCCFST short columnsThrough the calculation and comparison of 7 kinds of calculation formulas of ultimate bearing capacity of existing CFST structures at home and abroad under axial compression,it is found that the 7 kinds of calculation formulas listed in this paper can be used to judge the influence of the above four parameters changes on the bearing capacity of RBA-SCCFST.The calculated values of Cai Shaohuai formula,Zhong Shantong formula,JCJ01-89 and European formula are in good agreement with the experimental values,and the calculated values of the revised Han Linhai formula are in good agreement with the experimental values.It is suggested that the above five formulas be used to calculate the ultimate bearing capacity of the structure.(3)Finite element simulation of RBA-SCCFSTUsing the finite element analysis software ABAQUS to model and calculate,this paper studies the applicability of ABAQUS to simulate and calculate the axial compression performance of the structural specimen,and selects the appropriate methods for the establishment of the structural model,the selection of the constitutive relationship,the setting of the parameters,the interaction of the contact surfaces and the meshing of the finite element simulation calculation process.It is found that the failure mode,ultimate bearing capacity and load-strain curve of the simulated specimens are in good agreement with the experimental results,which proves that the finite element simulation method adopted in this paper is correct,and also shows that the finite element simulation method of this structure is similar to that of ordinary CFST structure.In addition,the mechanical properties of the structure under the influence of the wall thickness of the steel tube are extended by using the finite element method,and the constraint effect coefficient is extended to the range of 0.2?1.29.Through the simulation of five groups of specimens with the constraint effect coefficient of 0.2?1.29,it is found that the increase of the constraint effect coefficient can enhance the strength and ductility of the specimens.