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This paper presents an experimental investigation on the axial behavior of square ultra-high performance concrete (UHPC) filled steel tube columns (SUHPCFSTs). To this end, 32 short specimens are fabricated and tested in the presence of uniaxial compression. The confinement index is considered as a variable by changing the steel tube thickness and the UHPC strength. The roles of failure modes, load-deformation curves, ultimate load bearing capacity, and post-peak ductility of specimens are examined in some detail. The results indicate that the axial load-deformation curves can be classified into three distinct types with three stages based on the confinement index. Good ductility is observed for all specimens with the confinement index in the range of 1.41 to 5.27. The ductility and strength indexes grow by increasing of the confinement index, in spite that the increase of the strength index is insensitive. Additionally, the interaction between the UHPC and the steel tube is mainly treated in the ductility, not the load bearing capacity of columns. Finally, a revised calculation method for predicting the ultimate bearing capacity of SUHPCFSTs is proposed, and then, it is validated by the experimental results. |
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