Mechanical behavior of discontinuous cavity structures in prefabricated tunnels

• Three types of open-cavity structural members with circular, elliptical, and rounded-end cross-sections were designed and fabricated, and mechanical performance tests were conducted on these configurations. • Through a dual-index evaluation system incorporating flexural capacity and cavity deformation, the mechanical response characteristics and failure mechanisms of the cavity members were revealed. • The mechanism of the influence of cavity parameters on the bearing capacity, joint tension, concrete damage evolution and reinforcement stress distribution of lightweight components is elucidated. The influence of cavities on the mechanical properties of discontinuous components is complex and unknown. In this study, the mechanical properties of discontinuous cavity components and their influencing factors are studied by large-scale bending tests and numerical simulations. The objective was to explore the characteristic effects of cavity spacing, number of cavities, concrete strength, and reinforcement diameter on the flexural bearing capacity, joint opening, concrete damage, and steel stress of discontinuous cavity structures. The results demonstrate that the presence of cavities leads to a decrease in concrete volume and a decline in the component's ultimate load-bearing capacity. The circular-section cavity components exhibited the highest ultimate load capacity of 596.88 kN, while the circular-ended cavity components showed the lowest ultimate load capacity of 461.87 kN. A lower cavity ratio is associated with enhanced structural capacity. Specifically, reducing the cavity ratio from 15 % to 9 % results in a 49.29 % improvement in the component's load-bearing capability. A cavity ratio of approximately 10 % represents the optimal equilibrium between achieving lightweight design and maintaining structural strength. Furthermore, as the distance between cavities increases, the load-bearing capacity of interconnected components diminishes, accompanied by an expansion in joint separation.The strength of concrete are increased and increasing the number of cavities from 4 to 6 (keeping the cavity rate at 10 %) contributes to enhancing the bearing capacity of joint components and reduce the amount of joint opening. However, with the increase in reinforcement diameter, the overall benefit to the structure is negative. This study provides some beneficial results for lightweight design of prefabricated frame tunnels.