Mechanism of load introduction and transfer within steel-encased CFST members with shear connections

Abstract

This paper experimentally and numerically investigates the load introduction and shear transfer within steel-encased concrete-filled steel tube (CFST) members with shear connections. The effects of the cross-sectional slenderness, angle configuration, column length above and below the connection, and the internal reinforcing plate types were evaluated. The interfacial behaviour, including the degradation and failure of the chemical bond and the friction resistance, was simulated in the established finite element (FE) models, which were validated against the test results. Generally, the load introduction was developed from the upper column and within the full connection region, and the shear force could continue to transfer within each component underneath the connection. Compact members that meet the load allocation requirement from the tube to concrete infill can achieve the full design strength solely via direct bond interactions. An alternative transfer mechanism, i.e. direct bearing, can improve the interfacial load transfer capacity when appropriate reinforcing plates are used. The design approach for the direct bond transfer mechanism was proposed. The proposed approach can predict the bond resistance on the interface between the steel tube and concrete infill with reasonable accuracy.