Abstract: Hybrid fibers provide a crucial approach to improving the fire resistance, stray current corrosion resistance, and bearing performance enhancement of ultra-high performance concrete(UHPC) segments. Eccentric compression represents the fundamental stress state of segments. This study investigates the bearing capacity and deformation behavior of rectangular-section columns (200 mm × 400 mm) made of steel/polypropylene (PP) hybrid fiber-reinforced ultra-high performance concrete under eccentric compression. Based on the full-range load-displacement response and failure characteristics observed in tests, the research reveals the influence of section eccentricity and longitudinal reinforcement ratio on the failure mode, characteristic load points, and deformation capacity of the specimens. The difference in mechanical performance compared to C50 reference specimens is also examined. Testing results are as follows: (1) Compared to ordinary concrete columns under eccentric compression, the steel/PP hybrid fiber-reinforced UHPC columns exhibit a significant improvement in bearing performance, with their yield load, peak load, and ultimate load increasing by 62.04%, 58.13%, and 13.48%, respectively. (2) Parameter analysis shows that when the eccentricity increases from 150 to 300 mm, the deformation capacity of the members is improved. When the longitudinal reinforcement ratio increases from 0.67% to 0.79%, the deformation capacity is further enhanced, and the bearing capacity shows a positive correlation with the reinforcement ratio. (3) The hybrid fibers enable the tensile zone to continue providing resistance after cracking, contributing significantly to the development of bearing capacity and deformation in eccentrically compressed columns. Based on the experimental ultimate moment and combined with section capacity calculations, a suggested value for the equivalent coefficient k in the tensile zone is derived through back-calculation.

Key words: tunnel segment, hybrid fiber, ultra-high performance concrete, eccentric compression