A design procedure for the seismic protection of infilled frames by dissipative braces

Existing reinforced concrete frame buildings with non-ductile detailing suffered severe damage and caused loss of life during earthquakes. Different rehabilitation systems have been developed to upgrade the seismic performance of this kind of structures. The research discussed in this paper, carried out under the partial financial support of “convenzione Dipartimento di Protezione Civile- Consorzio RELUIS, signed 11/07/2005 (repertorio n. 540), research line 2, deals with the seismic protection of frame structures, in particular for the application presented buckling restrained steel braces (BRB) have been selected. A displacement-based procedure to design dissipative bracing for the seismic protection of frame structures is proposed and some applications are discussed. A two- fold performance objective is considered to protect the structure against the collapse and the non- structural damage by limiting global displacements and interstorey drifts. As an example, some r.c. frame buildings, designed according to the non-seismic Italian Code, have been analyzed also considering the infills and retrofitted with BRB via the proposed procedure. In order to assess the effectiveness of the proposed rehabilitation design procedure non linear static and dynamic time- history analyses have been performed. Concluding the necessity of performing dynamic analysis, instead of non linear static analysis, on structures with dissipative bracing systems has been discussed.