Experimental investigation on flexural performance of UHPC beams reinforced with steel-FRP bars

To investigate the flexural performance of Steel-FRP Composite Bars (SFCBs) reinforced Ultra-High Performance Concrete (UHPC) beams, eight concrete beams with different reinforcement ratio, types of concrete were designed and fabricated. Flexural performance tests were conducted to examine the effect of various parameters on bearing capacity, deflections, crack patterns, ductility, and failure modes. The results indicate a significant enhancement in the flexural capacity of tested beams with UHPC. The bearing capacity of SFCB–UHPC beam is higher than that of steel-reinforced UHPC beams, but less than that of FRP (Fiber-Reinforced Polymer) reinforced UHPC beams. The deformation and crack resistance ability of SFCB–UHPC beams fall between those of steel-reinforced UHPC beam and BFRP-reinforced UHPC beam. Increasing the concrete strength and SFCB reinforcement ratio can significantly enhance the deformation and crack resistance ability of SFCB–UHPC beam. All tested specimens exhibited ductile failure. At the serviceability limit state controlled by deflection/crack, the steel-reinforced UHPC beams and BFRP-reinforced UHPC beams exhibit the highest and lowest utilization factors of flexural capacity, respectively, and that of SFCB–UHPC beams falling in between. High-ductility UHPC enhances energy absorption, ductility, initial and secant stiffness. The reinforcement type has a minor impact on the energy dissipation of flexural beams. SFCB, on the other hand, enhances the ductility, initial and secant stiffness of specimens. Based on a simplified material constitutive model and fundamental assumptions, three failure modes for the SFCB–UHPC beam under bending were defined, along with their respective criteria. This enables the establishment of a simplified load capacity calculation formula. With reference to ACI440.1R-03, a stiffness calculation formula was developed to predict the deformation of SFCB–UHPC beams. This research can provide a technological reference for the design and analysis of SFCB-reinforced UHPC beams.