Cyclic Behavior of Embedded Column-to-Foundation Connections in Circular CFST Columns: An Experimental and Numerical Study

This study investigates the cyclic performance of embedded column-to-foundation connections in circular concrete-filled steel tube (CFST) columns through experimental testing and numerical simulations. While base-plate connections are commonly used in composite structures, embedding the column into the foundation provides notable advantages, including increased strength, stiffness, and ductility under seismic loading. Experimental results confirmed that embedded connections are capable of fully transferring axial and lateral loads. Failure primarily occurred through plastic hinge formation at the column base, with no evidence of brittle fracture or pull-out. Increasing the embedment depth (Le) significantly enhanced flexural capacity, energy dissipation, and cyclic stability. An embedment depth equal to the column diameter (Le = D) was sufficient to achieve full moment transfer, while deeper embedments (Le > ۱.۲D) further improved hysteretic behavior and mitigated stiffness degradation at large displacements. The circular geometry of the column, combined with confinement from the surrounding concrete, generated an effective triaxial stress state (i.e., compressive stresses in all three directions) that enhanced mechanical interlock between the steel tube and the concrete core. Numerical simulations corroborated the experimental findings and provided additional insights into stress distribution, confinement effects, and shear transfer mechanisms. Increased friction and contact area within the interaction zone contributed to greater initial stiffness and improved post-yield strength. Parametric analyses revealed that an axial load ratio up to ۰.۲, particularly in conjunction with high-strength concrete, enhanced seismic performance. However, higher axial ratios (e.g., ۰.۳) led to local buckling and reduced ductility. For optimal seismic design, it is recommended to embed the column to a depth at least equal to its diameter and maintain the axial load ratio within the range of ۰.۱ to ۰.۲.

کلیدواژه ها:

Embedded connection ، CFST column ، Cyclic behavior ، Axial load ، seismic performance ، Energy Dissipation