Structural Performance of Concrete-Filled Tube Columns Using UHPC Compared to Conventional Concrete

The primary objective of this research is to compare the performance of columns filled with Ultra-High-Performance Concrete (UHPC) and those filled with normal concrete (NC) under controlled axial compressive forces. The experimental program was designed to fabricate specimens of both UHPC- and NC-filled tubes in the laboratory, ensuring consistency in size, steel tube thickness, and curing conditions. Each specimen was subjected to standardized axial loading tests to examine parameters, such as peak load capacity, deformation characteristics, and failure modes. The analytical part of the study focused on developing and validating models that accurately predict the structural response and ultimate strength of these composite columns. Special attention was paid to assessing the influences of steel tube wall thickness on the interaction between the steel and the concrete core, as well as the effectiveness of UHPC in enhancing strength and ductility. UHPC and NC-filled steel tube columns exhibited similar load-deformation behavior up to the maximum load. Nevertheless, UHPC showed a rapid drop in strength after the peak due to lower bonding and confinement effects. Both materials failed in similar modes, showing drum-shape deformation at the ends and shear failure in the middle. Standard concrete-filled tube strength formulas were not reliable for UHPC, and increasing steel tube thickness was less effective for UHPC-filled columns than for those with normal concrete.