Load Transfer Mechanisms in Welded Fin Plate-to-CFST Column Connections

This study investigates the load transfer behavior in welded connections between fin-plates and concrete-filled steel tubular (CFST) columns. A detailed account of an experimental assessment, carried out on six full-scale load transfer specimens with varying cross-sectional slenderness and upper column lengths, is provided. Supplementary push-out tests and CFST stub column tests were undertaken to evaluate the bond characteristics and establish the reference compressive strength under full composite action. The test results reveal that load transfer primarily depends on the intricate bond interaction behavior at the steel-concrete interface, which is influenced by multiple parameters and is nonuniform along the column height. It is shown that the ultimate behavior typically involves tube buckling below the connection and relative slip between the steel tube and infill concrete, without achieving the full compressive strength of the stub columns. Detailed strain measurements also indicate limited utilization of the concrete strength, highlighting the need for a minimum upper column length to ensure adequate load transfer in slender CFST cross sections. Comparison with existing studies and design provisions shows that current standards overestimate the strength of noncompact and slender composite columns. This necessitates the introduction of proposed modifications in design procedures in order to capture accurately the influence of the key governing parameters including the sectional slenderness and load introduction length, leading to a more reliable prediction of the capacity of CFST columns with welded fin-plate connections.