Influence of different debonding gap types on mechanical performance of axially compressed CFST stub columns with same debonding arc-length ratio

The mechanical properties of concrete-filled steel tubular (CFST) members are influenced by the possible debonding gap between the steel tube and concrete core. To investigate this phenomenon, finite element models (FEMs) of the CFST columns with different debonding types, such as the circumferential debonding gap (CDG) and spherical-cap debonding gap (SDG), were established by using ABAQUS. The accuracy of the FEMs was verified comparing the obtained results with experimental ones. The verified FEMs were used to analyze the influence of different debonding types on the mechanical performance of the axially compressed CFST stub columns with the same debonding arc-length ratio (RD). The results showed that with an increase in RD, the ultimate load-bearing capacity (Nu) of CFST columns decreased. However, a critical RD (RD-cr) was found, in fact when the RD was less than or equals to the RD-cr, the influence of different debonding types on the Nu and failure modes of CFST columns were basically the same. When the RD was larger than the RD-cr, with an increase in RD, the Nu of SDG CFST columns decreased linearly, however, the Nu of CDG CFST columns decreased nonlinearly with gradually reduced decrease rates. Finally, it was found that the overall bending, inward and outward buckling in SDG CFST columns were more serious than those in CDG CFST columns.