Seismic retrofit of existing steel concentrically braced frame with friction dampers

Inthecontextoflowtointermediateseismichazardregion,thisMasterprojectevaluate,thanks to a case study, the potential of friction dampers as retrofit solution of existing Concentrically Braced Frames (CBF). Simple to design and economic to build, they are commonly used as Lateral-Load Resisting System in steel structures. In a country where most of the building were designed before the first seismic code, the need for innovative retrofit approach such as damped brace frame is significant. On the basis of past studies, this report assesses the current dynamic behaviour of the Civil Engineering building of the EPFL. The more representative frames are analysed thanks to non-linear time-history simulations, their behaviour is dissected and their weaknesses are highlighted. The seismic investigations are done according to the SIA norms and EC which recommend that the structure must undergo seven different ground motion simulations that represent the local seismic hazard. Unwanted behaviour is underlined: a problematic eccentricity of the brace connection and insufficiency frame element resistance prevent the CBFs to work properly. This poor performance exposes the building to brittle local failures and global collapse. A damped brace solution is designed to overcome this threat. Their protective capacities as well as the large flexibility in their activation forces allow to find a promising retrofit approach. While minimising the number of elements to change, the implementation of in-axis damper along the braces insures a protection to the weakest actual elements, a stable and effective energy dissipation and an improvement of the global dynamic response.