Un criterio di progetto per il rinforzo di telai in c.a. mediante controventi dissipativi

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: in particular, buckling restrained steel braces (BRB) offer many advantages. BRB differs from a conventional brace in that it is capable of yielding both in tension and compression instead of buckling thus exhibiting very favorable energy-dissipating characteristics. The present paper deals with the seismic protection of reinforced concrete frames. In particular a displacement-based procedure to design dissipative BRB for the seismic protection of masonry-infilled frames is proposed. A two-fold performance objective is considered to protect the structure against the collapse (ULS) and the non-structural damage (DLS) by limiting global displacements and interstorey drifts so that structural and infill integrity is granted under a given seismic event. Positioning these devices in a structure to maximize their effectiveness at minimum cost is a very important issue which is considered too. As an example, an infilled-frame building, designed according to the non-seismic Italian Code and thus only for vertical loads, is analyzed. After retrofitting with BRB via the proposed procedure, non linear static and dynamic time-history analyses to assess the effectiveness of the proposed rehabilitation design procedure are performed.