Shear strengthening of reinforced concrete beams using FRP-UHPC composite layer

This study presents a detailed examination of the shear strengthening of reinforced concrete (RC) beams by applying Fiber Reinforced Polymer (FRP)-Ultra-High-Performance Concrete (UHPC) composite layers. Ten beams were prepared and tested to assess the effectiveness of the FRP-UHPC layer in improving shear capacity, including eight beams strengthened with the FRP-UHPC layer and two control beams. The key variables influencing the strengthening performance included the type of fiber in the strengthening layer (steel fiber vs. polyethylene fiber), bonding methods (epoxy vs. surface treatment), and shear span-to-depth ratios (2.52 vs. 1.57). Experimental results demonstrated that the FRP-UHPC composite layer improved the stiffness and load capacity of strengthened beams for the two shear span‑to‑depth ratios studied. All beams exhibited a consistent shear-compression failure mode. The cracking behavior and failure mechanisms were further analyzed using Digital Image Correlation (DIC) techniques, which revealed that the fiber-reinforced FRP-UHPC composite layer effectively suppressed shear crack formation and reduced crack width. Micro-scale analyses confirmed a strong bond between the UHPC and the concrete matrix. A finite element (FE) analysis was also conducted to simulate the experimental tests, providing a comprehensive understanding of the mechanical behavior. The FE model results closely matched the experimental data, highlighting the model's accuracy in predicting the behavior of FRP-UHPC strengthened beams. These findings offer valuable insights for the design and application of the FRP-UHPC composite layer in strengthening RC structures. © 2025 Elsevier Ltd.