The Creep Of Core Concrete And Its Influence On The Mechanical Performance Of The Axially Compressed High Strength Concrete Filled Steel Tubular Member

The high strength concrete filled steel tubular member(HCFST) are increasingly applied to civil engineering construction in large quantity because of its super performance.,however, the shortage of full knowledge of creep of this member prevents us from further using it correctly and extensively .therefore.it's necessary to explore the mechanisms of creep of CFST member and influence of creep on mechanical performance of HCFST member. According to the applied stress level,the HCFST member is in two different states .we establish a uniform theory to calculate the creep of ACHCFST member. Based on the continuity of the stress-strain complete curve,we unite the multiaxial creep theory from Neville and uniaxial creep theory(theory of Elastic Continuation and Plastic Flow) to consistently calculate the creep of ACHCFST members. During creep, the internal force redistribution will occur and strain harmony will be preserved between steel tube and core concrete. According to the characteristic, we establish the calculation model of creep of ACHCFST members , deduce formula of the axial specific creep of ACHCFST members ,then work out program to calculate the creep of ACHCFST member and analysis the influence of creep on the mechanical performance of ACHCFST member. From calculation results, we discover the distinct character of ACHCFST member?the redistribution between steel tube and core concrete may not stop until the creep stops, or the redistribution have finished before creep stops ,which depends on the applied stress level. Under high applied stress, the redistribution will finish in advance, Moreover, the higher the applied stress is, the earlier the redistribution finishs. This speciality has great effect on the amount of creep ,unloading proportion of core concrete and stress path of steel tube ,and so on. To verify the validity of the calculation model, we made creep test of ACHCFST members on 6 groups of the specimens ,and experimental results demonstrate that the calculation model is feasible. To meet the need of practical engineering application . we provide a simple solution to considering influence of creep during the course of designing the ACHCFST membersIn addition,we design economical and high-efficiency steel-frame lever creep experimental mechanisms to complete the ACHCFST specimen creep test. It is a innovation in the field of high-stress loading system.