Shear-transfer mechanisms in ultra-high-performance concrete beams reinforced by externally web-bonded steel plates

This study investigated a reinforced ultra-high-performance concrete (UHPC) beam in which conventional stirrups were replaced with externally web-bonded steel plates on the web (RUB-WSPs) to enhance the structural efficiency and construction productivity. To study the shear performance, six rectangular specimens (four RUBs-WSPs and two stirrup-reinforced UHPC beams) were designed and tested. The influences of key parameters (the web-bonded steel plates (WSP) configuration and shear span-to-depth ratio ( λ )) on the ultimate shear capacity, failure modes, and load–strain responses were investigated. The results indicated that the RUB-WSPs exhibited a marginally lower shear capacity but superior ductility compared with the stirrup-reinforced beams. Specimens with a higher λ value had a greater ultimate midspan deflection, slightly reduced ultimate load, and different crack inclinations than those with a lower λ value. The WSPs provided a shear resistance comparable to that of conventional stirrups. Furthermore, the shear transfer mechanisms within the beams were analyzed. A theoretical method was developed to quantify the contributions of the individual UHPC components: the fibers, dowel action, shear reinforcement, and shear-compression (SC) zone concrete. Owing to the low λ , the SC zone concrete provided the largest contribution to the total shear capacity, whereas the dowel action contributed the least to the tested configurations. The shear capacity was predicted using a theoretical method and compared with the test results, which showed good agreement. This study established RUB-WSPs as a viable solution for advanced structures, offering practical advantages. Compared to stirrup-reinforced UHPC beams, RUB-WSPs enhanced the ductility and simplified the construction process.