Design of dissipative braces for an existing strategic building with a pushover based procedure

The research presented in this paper deals with the seismic protection of existing frame structures by means of passive energy dissipation. An iterative displacement-based procedure, based on capacity spectrum, to design dissipative bracings for seismic retrofitting of the frame structures is described, and some applications are discussed. The procedure can be used with any typology of dissipative device and for different performance targets. In this work, the procedure has been applied, with both traditional pushover (load profile proportional to first mode) and multimodal pushover, to an existing reinforced concrete (R.C.) frame building. In the application, the buckling restrained braces have been used in order to prevent damages to both the structure and non structural elements. The use of multimodal pushover proves to be more effective than pushover based on single mode in case of medium rise R.C. f rame building (higher than 30 metres) but, once this building is retrofitted, and therefore regularized, with a bracing system, the difference between using monomodal or multimodal pushover becomes insignificant.