Study On The Recycled Aggregate And Recycled Aggregate Concrete Used To Fill The Thin-walled Steel Tube Column

There have a lot of research results of recycled aggregate concrete（RAC）, and anumber of representative engineering projects have been constructed. But theproperties of the long-term shrinkage of RAC and the interfacial interaction force（IIF）between the thin-walled steel tube and the core concrete need more research,it’s also has some controversies about the influence of the IIF to the ultimate axialcompressive strength of the concrete filled steel thin-walled tubular column. So basedon the study of the physical and mechanical properties of recycled coarse aggregateand the recycled aggregate concrete mix, the long-term shrinkage properties of RAC,the IIF and it influence to the axial compressive ultimate bearing capacity of theconcrete filled steel thin-walled tubular column also have been studied. The researchresults can make people have further cognition of the workability of the recycledaggregate concrete filled thin-walled steel tube column. The research works just asfollows:Firstly, the physical and mechanical properties of recycled coarse aggregateproduced under factory conditions have been studied, and an analysis the differencebetween the natural coarse aggregate and the recycled coarse aggregate has beenmade. Continuous gradation of recycled coarse aggregate has prepared according tothe packing density index. There has made a mechanical comparison between theRAC and the natural aggregate concrete（NAC） within C40and C50concretestrength grade, some suitable design parameters of RAC mix for engineeringapplications were obtained finally.Secondly, the measures to suppressive the long-term shrinkage of RAC have beenstudied by adding mineral admixtures and the concrete expansion agents to the RACmix, and there also has made a difference comparison about the long-term shrinkagebetween the RAC and the reference NAC, some effective method to suppressive thelong-term shrinkage of RAC has been obtained. Thirdly,15axial push-out test specimens and15axial compressive test specimensof concrete filled steel thin-walled tubular column are completed, and got all the testspecimens’ load-displacement curves. The numerical simulation of the push-out testspecimens were conducted with the ANSYS program. There has a discussion aboutthe influence of the IIF to the ultimate axial compressive strength of the concretefilled steel thin-walled tubular column according the figures of the tests at the end ofthis part.Finally，Two prediction formulas were got according to the former figures, oneformula can be used to predict the ultimate axial compressive strength of the concretefilled steel thin-walled tubular column, the other can be used to calculate themaximum IIF between the steel thin-walled tube and the core concrete. There havemade a comparison about the computational accuracy between the predictionformulas and two building structure design codes calculation methods according tothe figures which have published.