SEISMIC PROTECTION OF SUBSTANDARD RC FRAMES THROUGH SELF-CENTERING DISSIPATIVE BRACES

Several existing reinforced concrete (RC) framed buildings require urgent retrofit interventions to meet modern seismic-performance requirements because of poor construction details, in-creased seismic hazard, change of intended use over their service life, or occurrence of materi-al degradation phenomena. Furthermore, these structures were designed considering outdated principles or even totally ignoring the seismic action. Among the possible retrofit strategies, an effective technique implies the use of metallic dampers installed in chevron braces and optimal-ly distributed in the structure to provide supplemental energy dissipation (and stiffening) effects. However, such conventional elasto-plastic dissipative braces (EPDBs) may suffer from recen-tering issues, because their working mechanism is, in general cases, based on the plastic de-formation of steel. Consequently, they exhibit permanent displacements at the end of the seismic event and need to be restored after each shaking. As an alternative, this contribution deals with the seismic protection of existing RC buildings through self-centering dissipative braces (SCDBs) that are featured by internal mechanisms nullifying the permanent deformation after their activation, thus offering significant advantages over EPDBs. We present a displacement-based design procedure for SCDBs implemented in RC framed structures targeting two per-formance requirements, namely the control of the roof displacement and the good recentering behavior of the structure after the seismic event. Then, we apply this procedure to the seismic protection of an archetypal building, representative of substandard RC frames built in 1960s-1970s in Italy, by comparatively illustrating the seismic performance of SCDBs and EPDBs through nonlinear time-history analyses.