Design methods for existing r.c. frames equipped with elasto-plastic or viscoelastic dissipative braces

Dissipative braces have proven to be very efficient devices for new buildings and seismic retrofitting of existing structures. In this paper a design method for dissipative braces based on elastic-plastic or viscoelastic behaviour, inserted in reinforced concrete existing frames with limited ductility, is proposed. The design method takes into account the dissipative behaviour of both the two components (r.c. frame and dampers). With regard to elastic-plastic devices, buckling restrained braces (BRBs) are considered, whereas High Damping Rubber (HDR) based devices are considered as viscoelastic devices. The behaviour of HDR is quite complex and both stiffness and damping depend on the strain amplitude and strain rate. Equivalent linear models may however be used to simulate their behaviour at a fixed displacement amplitude and frequency, with an acceptable approximation level.