Shear strength of functionally graded UHPFRC-NSC beams: Experimental and numerical study

Functionally graded reinforced concrete (FGRC) beams demonstrate a novel method for enhancing the resilience and durability of damaged or degraded structures. The selective application of the functionally graded concrete mixture in shear zones allows functionally graded concrete to optimize its advantages in high-stress areas, providing a cost-effective solution that maintains structural integrity and durability. This study investigates experimentally and numerically the shear strength of functionally graded reinforced concrete beams that incorporate normal-strength concrete (NSC) with ultra-high-performance fiber-reinforced concrete (UHPFRC). Five reinforced concrete beams were fabricated and assessed experimentally using a four-point bending test. Each beam had a cross-section of 180 mm in depth, 120 mm in width, and 1000 mm in length. Two beams were fabricated with an NSC mixture only, with and without stirrups. For the remaining beams, the third and fourth beams were cast with a combination of NSC and UHPFRC mixtures, where the UHPFRC was used in the critical shear regions with a width of 150 and 300 mm, and the fifth beam was cast with a full UHPFRC mixture. The study found that the beam without shear stirrups had a 50.4% decrease in load-carrying capacity. However, using the UHPFRC mixture instead of the NSC mixture in the shear zones by 150 and 300 mm (i.e., BS-UHPFRC-15 and BS-UHPFRC-30) resulted in a 51.9% and 92.5% increase in load-carrying capacity, respectively, compared to the BS-NSC-NS beam. In addition, the beam fabricated with a UHPFRC mixture in the whole beam showed superior performance compared to all beams, with an increased ratio of up to 167.0%. Functionally graded materials can enhance energy dissipation capacity by up to 40.0%. The FE models’ reliability was validated by the simulations, which in turn substantiated their suitability for future predictions. Overall, the results indicate that functionally graded beams significantly enhance shear strength and energy absorption, presenting considerable promise for the sustainable and cost-effective repair of damaged structures.