Study On Interfacial Bond Behavior Of Recycled Aggregate Concrete Filled Stainless Steel Tubes(RAC-FSST)

Recycled aggregate concrete filled stainless steel tube(RAC-FSST)is a new type of composite component,which is formed by filling recycled aggregate concrete(RAC)into stainless steel tubes.In addition to presenting the good bearing capacity and durability,this type of members also deal with the problems of high cost of stainless steel and poor mechanical properties of recycled concrete.These advantages make it have a wide range application prospects.For the concrete filled steel tube,the good interface between core concrete and steel tube is essential.However,the bond behavior of RAC-FSST columns may be inferior to the normal concrete filled steel tube,mainly due to the low surface roughness of the stainless steel and the larger shrinkage and creep of RAC.In this context,the interfacial bond behavior of circular RAC-FSST columns was studied in this paper.The main research works and results are summarized as follows:(1)A series of single and repeated push-out tests on 18 RAC-FSST specimens are performed.The main parameters include recycled aggregate replacement rate,cross-section diameter and diameter-thickness ratio.The failure patterns after the first push-out test,the bond stress-slip curves,the transverse and longitudinal strain distribution curves during four repeated push-out tests were investigated.The test results show that there are obvious stress peak points in the bond-slip curves of the RAC-FSST,and the free end of specimen shows distinct macro-interlocking phenomenon.(2)Based on the results of the bond-slip tests,the composition of interfacial bond stress for the RAC-FSST column was analyzed,the mechanism of the interfacial bonding under different slip stages was explored,and the change trends of the interfacial bond stress of the components was confirmed.The analysis present that the interface bond stress is mainly consist of mechanical interlocking force and frictional resistance when the bond stress reaches the bond strength;The relative size of the increase of the frictional resistance and the decrement of the mechanical interlocking force determine the growing trend of the τ-S curves of the specimen.(3)On the basis of the experiment results in this paper and the research of related literature,a bond strength database of total 90 specimens,including RAC-FSST,recycled aggregate concrete filled steel tube(RAC-FST)and concrete filled stainless steel tube(CFSST),has been established.The recycled aggregate replacement rates,cross-sectional geometric parameters and material types on the bond behavior of RAC-FSST were system evaluated.The results show that the bond strength of RAC-FSST column is generally lower than that of RAC-FST,and its bond strength is similar to that of CFST member with stainless steel tube;The bond strength of RAC-FSST members increases by 29%-96% with the increase of the recycled aggregate replacement rate;The more obvious the improvement effect of the replacement rate was observed in the specimens of smaller section diameter;As the cross-section diameter and the diameter-thickness ratio increase,the bonding strength decreases.(4)By summarizing and analyzing the existing prediction equations for the bond strength of concrete-filled steel tubes,the models for the bond strength of RAC-FSST column were proposed.Meanwhile,the bond stress-slip constitutive model of RAC-FSST column was established based on the 3-stage bond stress-slip relationship of CFST member.