The objective of this project is the seismic retrofit of an existent steel structure with buckling restrained braces (BRBs), and the proposition of a possible heightening. The structure that will be analysed is the GC building on the EPFL campus, in Ecublens. The structure has already been analysed in some previous studies and it has been highlighted that its seismic behaviour does not comply with current standards. Some solutions have already been proposed, as the reinforcement of gusset plates and the use of friction dampers. In this project a new solution will be evaluated, using BRBs to retrofit the structure. The advantage of this technology is that the structure becomes more flexible and at the same time more stable under a seismic load. In fact, BRBs do not experience buckling and their behaviour is hysteretic. With this new design, the number of connections and braces can be halved, decreasing the cost of the structure and eliminating weak points. A heightening of the structure will also be studied, as it was originally designed to be taller, and the EPFL is searching solutions for increasing the campus capacity.