تحلیل و طراحی ظرفیتی قاب‌های مهاربندی‌شده همگرای هلالی‌شکل و ارزیابی پارامترهای عملکرد لرزه‌ای و تقاضای انرژی

Crescent-shaped concentrically braced frames (CSCBFs) represent an innovative seismic-resistant system that blends the strengths of Special Concentrically Braced Frames (SCBFs) and Special Moment Frames (SMFs). SCBFs are valued for their high lateral stiffness, which limits seismic displacements, simplifies drift control, allows for smaller structural sections, and reduces costs. They are also easier to repair since braces can be replaced more readily than beams or connections. However, SCBFs restrict architectural flexibility due to diagonal braces that obstruct openings and suffer from poor post-buckling behavior, resulting in asymmetric hysteresis and reduced energy dissipation. SMFs, by contrast, eliminate diagonal braces, providing open layouts and superior architectural freedom. Their ductile seismic response arises from flexural yielding in beams, but this performance relies heavily on complex, precisely detailed beam-to-column moment connections. Thus, while SCBFs offer stiffness and simplicity, SMFs provide ductility and openness, qualities CSCBFs aim to integrate.
CSCBFs achieve this integration by employing crescent-shaped braces that resemble circular arcs. Unlike conventional concentrically braced frames (CBFs) with straight members subjected mainly to axial forces, the curved geometry in CSCBFs introduces strong axial-flexural interaction. This mitigates brace buckling and hysteresis asymmetry, improving ductility and energy dissipation. The system combines stiffness, ductility, and architectural flexibility in a single design philosophy.
To evaluate their seismic behavior, multi-story CSCBF archetypes with varying bay numbers, heights, and brace eccentricities are developed. Since no design codes currently address CSCBFs, these models follow SCBF provisions. A capacity-limited design methodology is applied so that braces act as energy-dissipating fuses, protecting beams and columns from inelastic damage, mirroring the SCBF philosophy of controlled damage and repairability. Nonlinear analysis methods are employed to assess performance. Fiber-based static pushover analyses provide key parameters such as ductility and overstrength factors, offering insight into deformation and strength capacity. In addition, nonlinear time history analyses with 11 pairs of far-field ground motions from FEMA P695 measure dynamic responses, including peak and residual drift ratios. These results are compared to seismic code limits to check compliance and safety. Findings indicate that current assumptions for the response modification factor (R) of CSCBFs may be too optimistic, highlighting the need for more conservative design provisions and further studies.
Energy-based evaluations further clarify system behavior. Analyses of hysteretic energy, damping energy, and kinetic energy show how seismic input energy is distributed. Results confirm that the capacity-limited strategy works effectively: beams and columns remain elastic, while braces absorb most seismic energy as sacrificial elements. This ensures both safety and repairability after strong earthquakes.
Overall, CSCBFs offer a promising structural system that combines the stiffness and simplicity of SCBFs with the ductility and openness of SMFs. By using curved braces to improve buckling resistance and energy dissipation, CSCBFs achieve a balanced performance that addresses both engineering and architectural demands. These findings support CSCBFs as a practical high-performing solution for seismic design, though refinement of design guidelines remains necessary.