Research On The Compressive Properties Of RRACFSTSC And STCRRACSC

With the acceleration of urbanization in China,a large amount of urban construction waste is generated,and the mining of natural concrete coarse aggregate needs to be at the cost of resources and environment.At this point,the application of recycled aggregate concrete(RAC)was born.RAC is a kind of green and environmentally-friendly material that uses solid abandoned concrete,brick-grain vermiculite as raw materials.Its extensive application in engineering practice also conforms to the concept of sustainable development,and can make a great contribution to the recycling of resources.However,there are problems with low strength,poor ductility,and large shrinkage of RAC,which cause them to be inferior to ordinary concrete in mechanical properties,and sometimes they cannot meet the needs of practical engineering,which limits the application of RAC in practical engineering.Aiming at the problems of low compressive strength,large shrinkage and creep of RAC,and low load-carrying capacity,ductility and seismic performance of ordinary reinforced concrete.RAC filled steel tubular,adding reinforced cages continues to expand the constraint RAC,the reinforced recycled aggregate concrete-filled steel tubular(RRACFST)and the steel tube confined reinforced recycled aggregate concrete(STCRRAC)models are proposed.The external steel tube is used to constrain the RAC,and the internal reinforced cages further constrains the RAC,transforming the RAC from one-way compression to three-way compression,and the material changes from a brittle material to a plastic material,thestrength and ductility of RAC are improved,and the comprehensive mechanical properties of the RRACFST and STCRRAC are strengthened.In this paper,the load-carrying capacity of 36 the RRACFSTSC and STCRRACSC are analyzed by using finite element method and theoretical research,with the main parameters of steel tube diameter thickness ratio,steel tube width thickness ratio,recycled coarse aggregate replacement rates,reinforcement ratio and constraint effect coefficient.The main work completed is as follows:1)In order to understand the mechanical properties of the RRACFSTSC and STCRRACSC,based on the component geometry nonlinear,material nonlinear and plastic damage constitutive of RAC,by using nonlinear finite element analysis technology,the nonlinear finite element analysis model of the RRACFSTSC and STCRRACSC are established,and the process and method of finite element modeling are introduced in detail.The research has high scientific research value.2)Using the limit equilibrium analysis method,the ferrule principle,and the double shear unified strength theory,the load-carrying capacity calculation method of the RRACFSTSC and STCRRACSC are proposed.The influence of the steel tube diameter thickness ratio,steel tube width thickness ratio,the recycled coarse aggregate replacement rates,the reinforcement ratio,and the constraint effect coefficient are considered.Through the comparison of literature test and finite element simulation,it are found that the the load-carrying capacity calculation method of the RRACFSTSC and STCRRACSC are also applicable to the RCFSTSC and STCRCSC,and the RACFSTSC and STCRACSC.3)The analysis of axially-compressed members shows that due to the complexity of the RAC structure,the recycled coarse aggregate replacement rates has fluctuation effect on the load-carrying capacity of RRACFSTSC and STCRRACSC,but the degree of influence is not large;The reinforced cages are arranged in the RACFSTSC and STCRACSC,the contribution of the reinforced cages makes the RRACFSTSC and STCRRACSC have higher bearing capacity and ductility performance than the RACFSTSC and STCRACSC;The steel tube diameter thickness ratio and the steel tube width thickness ratio has a more obvious effect on the load-carrying capacity of the RRACFSTSC and STCRRACSC.The smaller the steel tube diameter thickness ratio and steel tube width thickness ratio,the stronger theconfinement effect of steel tube on RAC,and the higher the load-carrying capacity of the RRACFSTSC and STCRRACSC.4)As the outer steel tube of the RRACFCSTSC directly bears the external load,the outer steel tube has yielded out of the constraint working state before the members reach the limit,so the load-carrying capacity of the RRACFCSTSC is not as high as CSTCRRACSC.5)The proposed the RRACFSSTSC and SSTCRRACSC can not only make up for the defects of weak restraint ability and poor ductility in the middle of square steel tube wall to RAC,but also has the advantages of simple construction and convenient connection,and has a broad application prospect.