Dissipative Elliptic-Braced Steel Frames for Seismic Retrofit of RC Buildings

Dissipative elliptic-braced steel frames (ELBRFs) represent an innovative solution for the seismic retrofit of reinforced concrete (RC) buildings, combining enhanced structural performance with minimal architectural intrusion. When installed within frame bays, elliptic braces preserve façade openings while providing significant energy dissipation capacity. This study investigates the effectiveness of ELBRFs as a dual lateral force-resisting system, integrating moment-resisting frames with dissipative bracing elements, with the aim of improving the seismic response of existing RC structures. The research combines experimental evidence and advanced finite element modeling to assess the global and local behavior of elliptic-braced systems under seismic loading. Cyclic quasi-static analyses are used to calibrate a refined fem model. A displacement-based design procedure is applied to size all the elements of the elliptic-braced steel frames. Nonlinear simulations are used to evaluate key performance parameters, including stiffness, strength, ductility, hysteretic behavior, and energy dissipation capacity. The results demonstrate that elliptic braces promote stable and symmetric hysteretic responses, with significant enhancement in energy dissipation and delay in the onset of global failure mechanisms.