Review on mechanical properties of fiber-reinforced cementitious composite-encased concrete-filled steel tube composite columns

To integrate dispersed studies and clarify the mechanisms underlying performance enhancement, a systematic review of over 110 studies in China and abroad was conducted to promote the practical engineering application of fiber-reinforced cementitious composite (FRCC)-encased concrete-filled steel tube (CFST) columns (hereafter referred to as FRCC-CFST columns) in steel-concrete composite bridges. Following the sequence of "material → interface → member → design → application", the research progress and practical applications of three typical FRCC encasing materials, including engineered cementitious composites (ECC), ultra-high performance concrete (UHPC), and hybrid fiber-reinforced cementitious composites (HFC), in FRCC-CFST columns were comprehensively summarized and analyzed. The results indicate that, at the material level, the three types of FRCC exhibit distinct advantages. ECC shows the best ductility, UHPC provides the highest load-bearing capacity, and HFC demonstrates intermediate overall performance. At the interface level, the high bonding strength and fiber-bridging mechanisms of FRCC help delay spalling of the encasement and enhance composite action. Measures such as installing shear studs, adding interface reinforcement, or increasing interface roughness can effectively enhance the steel tube-FRCC bond strength and improve the failure mode. At the member level, FRCC-CFST columns exhibit significantly superior performance under various conditions, including axial compression, eccentric compression, bending, shear, seismic, impact, and high temperature, compared with conventional CFST composite columns encased with ordinary concrete. The degree of performance enhancement is closely related to the FRCC type and structural confinement. At the design level, some mechanical models have demonstrated good predictive capability. However, existing design codes do not fully consider the high ductility and interface characteristics of FRCC, resulting in conservative load-bearing capacity evaluation. At the application level, UHPC-encased CFST columns have been validated in engineering practice, such as the Haixin Bridge in Guangzhou. In contrast, ECC- and HFC-encased CFST columns are still mostly in the experimental stage, limited by factors such as cost, construction adaptability, and the lack of design specifications. Future research should focus on the stability of medium and long columns, multi-hazard coupled responses, and interface cooperative mechanisms, so as to promote the development of a complete design theory and engineering application system and facilitate the standardized and large-scale application of FRCC-CFST columns.