Displacement-based design of buckling-restrained braces for the seismic rehabilitation of existing r.c. frames

Existing r.c. frame buildings with nonductile 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 conventional braces in that it is capable of yielding both in tension and compression instead of buckling thus exhibiting very favorable and stable 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 existing r.c. frames is proposed. This procedure can be easily applied to multi-fold performance objective to protect the structure against collapse and to avoid non-structural damage by limiting global displacements and interstorey drifts so that structural and infill integrity is granted under a given seismic event. As an example of seismic rehabilitation design, both a case study bidimensional r.c. frame and a real tridimensional wall-frame building are considered. The procedure is proved to be effective and promising even if further analyses are needed for a complete validation.