Nonlinear hinge models for seismic performance evaluation of concrete-filled steel tubular structures

Concrete-filled steel tube (CFST) columns are widely used in modern steel structures due to their superior strength, stiffness, and ductility compared to steel hollow structural sections (HSS). However, existing nonlinear hinge models inadequately capture the complex steel–concrete interaction under cyclic loading, and current design standards (e.g. ASCE 41–23 and AISC 342–22) lack detailed provisions for square CFST columns. This study develops a regression-based nonlinear hinge model, calibrated against 11 experimental datasets. The proposed five-point backbone curve explicitly accounts for strain hardening, confinement-dependent degradation, and axial-moment interaction – factors often oversimplified in prior models. Implemented in ETABS via a kinematic hysteresis model, the approach demonstrates high accuracy (±8% error in yield strength, ±5% in ultimate capacity) compared to conventional plastic hinge methods. A practical demonstration on a 15-story CFST moment-resisting frame (MRF) using nonlinear pushover and nonlinear response history analyses (NRHAs) showcases a 22% improvement in displacement ductility and an 18% reduction in residual drift under nine real earthquake records, meeting performance-based seismic design goals. CFST columns outperform HSS columns in strength and deformation capacity. This model addresses gaps in composite structural analysis, offering a practical and calibrated tool for high-seismic design and advocating for the design of code updates.