Experimental and numerical investigation on flexural performance of ultra-high-performance fiber-reinforced concrete (UHP-FRC) hollow panels with different longitudinal reinforcements

Prefabricated hollow panels with ultra-high-performance fiber-reinforced concrete (UHP-FRC) offer an efficient approach of reducing dead load by removing low-stress concrete while maintaining flexural efficiency. However, the interaction between different UHP-FRC and longitudinal reinforcements remains inadequately understood. This study addresses this gap through a combined experimental and numerical investigation on flexural performance of 18 hollow panels fabricated with ultra-high-performance concrete (UHPC), ultra-high-strength engineered cementitious composite (UHS-ECC), and lightweight high-strength ECC (LW-ECC), reinforced with steel bars, carbon FRP (CFRP) bars, or steel-FRP composite (SFC) bars. A stiffness-equivalent reinforcement design enabled meaningful cross-comparison among reinforcement types. Results reveal a strength-deformability trade-off governed by reinforcement selection. SFC-reinforced panels achieved the highest flexural capacities in all concrete groups, reaching 75.2 kN (UHPC), 79.5 kN (UHS-ECC), and 64.6 kN (LW-ECC), representing 52–77% increases over steel-reinforced counterparts and exhibited smoother post-peak softening than CFRP-reinforced panels due to ductility from the steel core. Steel-reinforced ECC panels demonstrated exceptional deformation capacity, with peak deflections of 34.2 mm (UHS-ECC) and 44.3 mm (LW-ECC) and stable post-peak load retention. A nonlinear finite element model, calibrated against experimental results (errors <10% for key response points), was employed for parametric studies on void size and reinforcement ratio for CFRP reinforced LW-ECC panels.