Research on Long-Term Performance of High-Strength Self-Compacting Concrete-Filled Steel Tubes at Early Age

High-strength self-compacting concrete-filled steel tube is a high-performance composite component formed by filling high-strength self-compacting concrete into steel tubes and adding a high-quality expansion agent. It has become a development trend for large-scale CFST structures. Long-term deformation will aggravate the deformation of vertical members. Owing to the inconsistent deformation of vertical members and the gradual accumulation of such differences， additional internal forces may arise in horizontal members， which may even cause structural tilting and affect the normal service function of the building. However， research on the influence of early-age loading on the long-term performance of high-strength self-compacting concrete-filled steel tubes is very limited. Therefore， in this paper， long-term deformation tests were conducted on 16 circular high-strength self-compacting concrete-filled steel tube short columns， divided into 8 groups. The concrete stress level was 0.3， and the loading duration was 90 days. The effects of concrete strength （C60， C80） and loading age （3 d， 7 d， 14 d， 32 d） on the long-term performance were investigated. Numerical analysis was also performed on high-strength self-compacting concrete-filled steel tubes： based on the modified EC2 shrinkage and creep model for self-compacting concrete with mineral admixtures， the effects of fly ash content and silica fume content on the long-term deformation were analyzed using the step-by-step integration method. The test results showed that the creep of C60 specimens first increased and then decreased with the increase of loading age， while the creep of C80 specimens gradually decreased with the increase of loading age. The parameter analysis results indicated that under single-admixture conditions， the long-term deformation of the members increased with the increase of fly ash content and silica fume content； under composite-admixture conditions， during the late-age loading stage， the long-term deformation decreased with the increase of fly ash content and silica fume content.