Mathematical models for ultimate moment capacity and flexural stiffness of concrete-filled steel tube beams

Concrete-filled steel tube (CFST) is considered a promising solution for enhancing the structural performance of steel structures. This paper presents the development of empirical model for predicting the ultimate moment capacity and flexural stiffness of composite beams, emphasizing the interaction between the concrete core and steel sections. A comprehensive comparison was conducted between the experimental results collected from past studies and the predicted results from existing standards and analytical methods. The existing design models reveal significant inconsistencies and inaccuracies in predicting the results. To address this issue, Grey Correlation Analysis (GCA) was conducted to address the sensitivity of the key parameters influencing the moment capacity and flexural stiffness of CFST beams. The proposed formula considers the key parameters, including confinement ratio (xi), geometric properties (t/D), materials strength (fck and fy), and the elastic modulus of materials (Es and Ec), to improve the precision and practical applicability of the empirical formula. A reliable group of experimental and numerical database were collected from past research to predict the ultimate moment, initial stiffness, and serviceability-level stiffness. Validation was conducted based on the results collected from past research to ensure the applicability and reliability of the developed empirical formula. Furthermore, the predicted value from new methods were compared with the results obtained from the published literatures. The proposed models demonstrate good agreement and better consistency with the experimental results.