Experimental Study on Shear Behavior of UHPC-NC Composite Members with Varying Thicknesses: Comparison with Conventional RC Beams

This study innovatively investigates the shear behavior of UHPC-NC composite members by systematically varying key parameters—UHPC interface configuration (ribbed form), thickness (30 mm, 40 mm, 50 mm), stirrup ratio, and shear span ratio. Static loading tests were conducted on four Ultra-High Performance Concrete Reinforced (UR) beams and identical-section Reinforced Concrete Beam (RCB) counterparts. Results reveal that UR beams exhibit 150%–200% higher cracking loads, 31%–48% greater ultimate shear capacity, and significantly enhanced stiffness and ductility compared to RCB beams. Crucially, the UHPC-NC configuration transforms the brittle shear failure mode observed in RCB beams into a ductile flexural failure mode. Furthermore, steel fibers within the UHPC synergize with stirrups to progressively resist shear deformation, effectively mitigating the widening of main cracks. A quantitative relationship between UHPC thickness and shear performance was established, providing valuable engineering design guidelines for bridge reinforcement and semi-precast construction applications. These findings demonstrate the substantial benefits of UHPC integration in enhancing the shear resistance and failure characteristics of composite structural members.