Assessment of seismic design parameters of moment resisting RC braced frames with metallic fuses

• Ductility demands (μ) of HEDDs increases as postyielding stiffness increases.
• To get the desired failure mechanism, stiffness parameter β should be 0.5 < β < 1.
• For the same failure mechanism, stiffness parameter α should be 0.25 < α < 0.5.
• Overstrength factor Ω tends to increase as α increases.
• Ductility factor Q tends to decrease as the number of stories increases.

A parametric study was devoted to evaluate, using static nonlinear analyses (pushover), global seismic design parameters for low to medium rise regular reinforced concrete moment-resisting braced frames (RC-MRBFs) with hysteretic energy dissipation devices mounted on chevron steel bracing. Frame models with range from five to twenty five stories were designed using different elastic stiffness ratios between the moment frame system and the whole structure (frame-bracing-hysteretic device system). Also, different elastic stiffness balances between the hysteretic device and the supporting braces were considered. Different post to pre yielding stiffness ratios for the hysteretic devices were considered. Two angles of inclination of the chevron braces with respect to the horizontal axis were considered, taking into account typical story heights and bay widths used in Mexican practice. From the results obtained in this study, stiffness balances are defined to achieve a suitable mechanism where the hysteretic devices yield first and develop their maximum local displacement ductility, whereas in the moment frame incipient yielding is only formed at the beam ends. Finally, additional comments are made with respect to: (a) relations between global ductility capacity and local displacement ductility capacity for the hysteretic devices for a given combination of the studied stiffness parameters and angles of inclination, (b) story drifts at yielding and their relation with the selected elastic stiffness ratio between the moment frame system and the whole structure and, (c) overstrength factors for design purposes.