Shear behavior of RC beams without stirrups made of concrete core and external prefabricated U-shaped UHPFRC plates

This study investigates the shear behavior of innovative T-shaped composite reinforced concrete (RC) beams without stirrups. The novelty of this study lies in investigating the shear behavior of stirrup-free, T-shaped composite beams that use an encased UHPFRC plate configuration as integrated permanent formwork. Six T-beams were tested: one RC reference beam and five composite beams with 30mm thick UHPFRC plates. Variables included interfacial properties (smooth, rough, anchored) and plate configurations (terminating at flange bottom or embedded within). One beam used cellular lightweight concrete (CLC) blocks to assess core concrete type. Four-point loading tests revealed that the UHPFRC plates significantly enhanced structural performance, increasing shear strength by up to 110.4% and deformation capacity 381.3% compared to a conventional RC beam. Critically, embedding the UHPFRC plates into the concrete flange with a rough interface proved to be the most effective configuration. This approach transformed the failure mode from brittle shear to ductile flexure and prevented premature debonding. This composite system presents a promising approach for enhancing the structural performance and durability of RC beams.