Design Procedure for Buckling Restrained Braces to Retrofit Existing R.C. Frames

Abstract eng:
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 before being subjected to an earthquake: 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. A numerical study to investigate its seismic behavior with and without BRB is carried out. Non linear static and dynamic time-history analyses to assess the effectiveness of the proposed rehabilitation design procedure are performed.

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