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<p>Semi-rigid connections fundamentally alter the dynamic behavior of steel structures, yet their height-dependent effects remain inadequately quantified in current design practice. This computational study employs nonlinear time-history finite element analysis using the Al-Bermani hysteretic model to systematically investigate dynamic amplification across nine single-bay portal frame configurations (1–25 stories) under harmonic excitation. Three distinct height-dependent behavioral regimes emerge: a growing amplification zone (1–16 stories, displacement amplification factors 0.23–1.87), a saturation zone (8–16 stories, factors 1.75–1.87), and a declining zone (16–25 stories, factors 1.73–1.87). The anomalous 1-story result (R = 0.23) is attributed to resonance detuning: the rigid frame operates at near-resonance with the excitation frequency, and the semi-rigid frequency shift eliminates this condition. Frequency reductions ranging from 25.7 to 49.5% follow a logarithmic relationship (R<sup>2</sup> = 0.666). The semi-rigid to rigid period ratio increases from 1.34 for a single story to 1.83 for 25 stories, demonstrating strongly nonlinear compounding of flexibility effects with height. Equivalent viscous damping from hysteretic connection behavior decreases from 9.8% (1-story) to 0.033% (25-story). Individual connection rotation demands remain remarkably stable at 19.2–22.8 mrad across all multi-story configurations, indicating that global displacement amplification is driven by accumulation of similar-magnitude rotations across increasing numbers of connections rather than by increasing individual demands. Findings and empirical formulas apply specifically to single-bay portal frames with α ≈ 0.44 and uniform member sizing.</p>

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Height-Dependent Dynamic Amplification in Multi-story Steel Frames with Semi-rigid Connections: From Energy Dissipation to Critical Instability

  • 期刊论文

  • 发表日期：

    2026年6月22日

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  • Djamel Aouiche,
  • Noureddine Lahbari

摘要

Semi-rigid connections fundamentally alter the dynamic behavior of steel structures, yet their height-dependent effects remain inadequately quantified in current design practice. This computational study employs nonlinear time-history finite element analysis using the Al-Bermani hysteretic model to systematically investigate dynamic amplification across nine single-bay portal frame configurations (1–25 stories) under harmonic excitation. Three distinct height-dependent behavioral regimes emerge: a growing amplification zone (1–16 stories, displacement amplification factors 0.23–1.87), a saturation zone (8–16 stories, factors 1.75–1.87), and a declining zone (16–25 stories, factors 1.73–1.87). The anomalous 1-story result (R = 0.23) is attributed to resonance detuning: the rigid frame operates at near-resonance with the excitation frequency, and the semi-rigid frequency shift eliminates this condition. Frequency reductions ranging from 25.7 to 49.5% follow a logarithmic relationship (R2 = 0.666). The semi-rigid to rigid period ratio increases from 1.34 for a single story to 1.83 for 25 stories, demonstrating strongly nonlinear compounding of flexibility effects with height. Equivalent viscous damping from hysteretic connection behavior decreases from 9.8% (1-story) to 0.033% (25-story). Individual connection rotation demands remain remarkably stable at 19.2–22.8 mrad across all multi-story configurations, indicating that global displacement amplification is driven by accumulation of similar-magnitude rotations across increasing numbers of connections rather than by increasing individual demands. Findings and empirical formulas apply specifically to single-bay portal frames with α ≈ 0.44 and uniform member sizing.