Optimization Analysis of the Mechanical Properties of CFST X-Shaped Column Joints for Indirect Cooling Towers

This study focuses on the application of concrete-filled steel tubular （CFST） X-shaped columns in the lower support structures of indirect cooling towers in thermal power plants. These structures have been widely applied in engineering practice due to their excellent bearing capacity and seismic performance. However， the mechanical properties of the X-shaped columns， particularly at their middle， upper， and lower joints—specifically the steel tube stress levels and interface slip—directly impact the safety and durability of the structure. Therefore， an in-depth analysis of the joint performance is of significant theoretical and practical value. Based on the plastic-damage model for confined concrete and the elastic-plastic hardening model for steel， this study employed the ABAQUS finite element analysis software to establish a refined 3D shell-solid element model for CFST X-shaped column joints. The modeling process included detailed construction of joint regions， incorporating components such as internal vertical stiffeners， tie bars， external vertical stiffeners， and external ring plates. To ensure model accuracy， this study referenced existing experimental data on the mechanical properties of middle joints in CFST X-shaped columns to validate the model’s reliability through comparative analysis. Through numerical simulations of various joint configurations， this study thoroughly analyzed the effects of internal vertical stiffeners， tie bars， external vertical stiffeners， and external ring plates on the steel tube stress levels and interface slip of the middle joint. The results indicated that：1） The middle joint of the CFST X-shaped column primarily bore axial pressure. Due to the connection of two semi-circular steel tubes that were not fully enclosed， the stress levels in the steel tube were relatively high. Adding internal vertical stiffeners significantly reduced the steel tube’s stress levels， enhanced the joint’s bearing capacity， and improved the mechanical properties of the middle joint. 2） In the upper and lower joints， large bending moments made interface slip a critical issue. By incorporating tie bars， interface slip could be effectively reduced， improving the overall stability of the joints. Optimizing joint configurations was a crucial approach to enhancing the mechanical properties of CFST X-shaped columns. Using the plastic-damage model for confined concrete and the elastic-plastic hardening model for steel， this study established a design optimization model for CFST X-shaped columns， laying a solid theoretical and practical foundation for future research on the safety and durability of indirect cooling tower support structures.