A design procedure for seismic retrofitting of reinforced concrete frame and concentric braced steel buildings with dissipative bracings

The research presented in this paper deals with the seismic retrofitting of existing frame structures by means of passive energy dissipation. An iterative displacement based pro cedure, based on capacity spectrum is described and some applications are discussed. The general procedure has also been discussed referring to the case of existing steel concentric braced frame structures (CBF). 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 r.c. frame building. In the application presented 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. frame 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 not significant.