The beam-column joints, as the key load-transfer components in concrete frames, their structural and mechanical properties directly influence the construction efficiency and the overall seismic performance of the entire system. By embedding fiber-reinforced polymer (FRP) tubes in the core area of the joints, a FRP tube-concrete composite joint is formed, which can effectively alleviate the shear failure that is prone to occur in traditional concrete joints and the construction difficulties caused by excessive spacing of stirrups. The achievements obtained by Beijing University of Technology in the 2024 NEXCEL TDA Project, titled "Design and application of novel FRP tube-concrete composite structures", have been successfully applied to the Lize Digital Financial Technology Demonstration Park project in Fengtai District, Beijing. This has significantly enhanced the shear bearing capacity of the core area of the node and effectively alleviated the problem of excessive rebars, providing a favorable demonstration effect for the large-scale promotion of FRP tubes in the construction industry.
The project selected the basement of the main structure as the application area. Regarding the issues such as congestion of stirrups in the joint core region and associated construction difficulties, typical beam-column joints at the top of the basement were chosen, and four FRP tubes with a fiber layup of ±45° were embedded in each node to replace part of the stirrups. The diameter of the FRP tubes is 150 mm, the height is 1000 mm, and the wall thickness is 5 mm. Before construction, the FRP tubes were pre-positioned and drilled to ensure that the longitudinal rebars can pass through smoothly, shown in Figure 2.
On-site Construction
FRP tubes have the advantages of flexible design, light weight, high strength, and excellent durability. When placed within the joint core area of the node, they not only effectively enhance the shear capacity of the area, but also significantly reduce the amount of stirrups, alleviating the difficulties in binding and the potential quality issues during concrete pouring caused by the dense placementof stirrups. The successful application of the FRP tube-concrete composite structure in this project provides a new engineering practice path for the research and development of high-performance joints,and promotes the further application and development of high-performance FRP materials in the construction industry.