Mechanical Characteristics of Cracked Lining Reinforced with Steel Plate–UHPC Subjected to Vertical Load

The steel plate reinforcement method is widely used for strengthening damaged linings. Nevertheless, low durability is one of the disadvantages of the steel plate reinforcement method, which uses epoxy resin as the interface binder. To enhance the load-bearing performance and strengthening effect of steel-plate-reinforced structures, this study introduced ultra-high performance concrete (UHPC) as the reinforcing bonding layer and proposed a novel method for steel plate–UHPC reinforcement of cracked linings. A mechanical performance model test was conducted on a 1/5 scale lining model using a loading test device to evaluate the load-bearing performance and stress deformation of both conventional steel plate and steel plate–UHPC reinforced cracked linings. The characteristics, mechanisms of failure, and impacts of strengthening of the steel plate reinforcement method and steel plate–UHPC reinforcement method for cracked linings were compared. A numerical simulation model was developed to investigate the reinforcement effect of cracked linings using steel plate–UHPC reinforcement. The analysis included examining the influence of steel plate thickness, UHPC bonding layer thickness, and reinforcement timing. Model test results show that the overall damage mode of the steel plate–UHPC-reinforced structure had good elastic–plastic behaviour, and the deformation and damage process under the vertical concentrated load can be divided into four typical phases. Compared with the traditional steel plate reinforcement, the ultimate load-carrying capacity and ductility of the steel plate–UHPC-reinforced structure were increased by 53% and 366%, respectively, showing significantly better load-carrying capacity and deformation performance. Numerical simulation results show that the reinforced structure’s load-carrying capacity and stiffness enhancement rate increased non-linearly with the increase in UHPC layer thickness and steel plate thickness. However, reasonable reinforcement timing exists for steel plate-UHPC reinforcement, and too late reinforcement timing leads to a decrease in structural load-carrying capacity and stiffness enhancement rate.