Stress Mechanism and Design Method of UHPC-Encased CFST Column-to-Beam One-Side Bolted Joints

One-side bolted connecting technique ensures the access of inside into the closed-section column, which has been used in the assembled joints between concrete encased CFST (CECFST) columns and steel beams. However, the bulge of steel tube and outer concrete were detected for one-side bolted normal CECFST column joints owing to the limited strength of outer concrete. Therefore, UHPC was adopted as outer concrete to replace the traditional outer concrete in CECFST columns, which aimed to avoid the steel tube from being failure effectively and to omit reinforcements in outer concrete for convenient installation in one-side bolted joints. A finite element model was established by ABAQUS considering the constitutive relations of complex materials and the convergence of multi-contact in joint region. The accuracy of the model was verified through test results, systematically revealing the restraining effect of outer concrete on interral steel tubes, and indicating that the UHPC could effectively restrict the bulge of steel tube. A parametric analysis were conducted on typical UHPC encased CFST composite columns one-side bolted to steel beam joints. Finally, the analytical models on the moment resistance were developed based on the component method. The comparison results declared that the proposed analytical method provided a reasonable prediction of the moment resistance. The research results in the paper validated that replacing normal concrete of CECFST by UHPC could avoid column failure when using one-side bolted joints and gave a proper design method for UHPC-encased CFST composite column one-side bolted to steel beam joints.