Continuity of seismic performance of concrete-filled steel tubular columns across strength sequence variation from NSC through HSC to UHSC

This study evaluates the continuity of seismic performance in square concrete-filled steel tubular (CFST) columns as concrete strength progresses from normal-strength concrete (NSC) through high-strength concrete (HSC) to ultra-high-strength concrete (UHSC). Through integrated experimental testing and numerical modeling, the research reveals how key performance metrics—hysteretic behavior, energy dissipation, ductility, and failure modes—evolve continuously across the strength spectrum. Experimental results demonstrate a progressive enhancement in load-bearing capacity (peak load increases by 46.5 % from C30 to C120) but a gradual decline in ductility (ductility index drops by 43.2 %) and energy absorption (ultimate damping coefficient decreases by 43.4 %), underscoring the inherent trade-offs governing performance continuity. A validated OpenSees model, extended to 182 parametric cases, further confirms that higher axial compression ratios amplify brittleness in UHSC columns, reducing post-peak displacement compared to NSC; higher slenderness ratios disproportionately diminish load capacity and elevate peak displacement in high-strength columns; wider width-to-thickness ratios enhance flexural capacity and displacement resilience in NSC, though benefits diminish with concrete strength. Overall, increasing concrete strength systematically elevates load capacity but reduces ductility, forming a nonlinear strength-ductility continuum where UHSC’s superior stiffness and load-bearing capacity are offset by brittle failure mechanisms. By bridging NSC, HSC, and UHSC behaviors, this study establishes a framework for optimizing CFST columns to maintain performance continuity under evolving material and loading demands in earthquake-resistant structures.