The seismic retrofit by external dissipative systems: A case study

External dissipative systems are seismic retrofit solutions for existing building frames that present some feasibility advantages with respect to more classic solutions involving dissipative devices installed within existing frames. This study analyses and compares the effectiveness of three alternative external retrofit configurations based on the use of fluid viscous dampers (FVDs) with reference to a case study involving the seismic upgrading of a typical school r.c. frame. In particular, the three considered systems are: a rocking base system consisting of a pinned-rocking braced frames equipped with fluid viscous dampers at their base, a fixed base system consisting of external fixed-base braced frames connected to the frame through dampers located at floor levels and a diagonal bracings system similar to the traditional arrangement, but installed adjacent to the frame. All the proposed retrofit solutions are analysed taking into account the non-linear behaviour of the r.c. frame building (designed with inadequate seismic detailing) and both the linear and non-linear behaviour of the FVDs. The obtained results show that all the systems are effective solutions, even if performances in terms of interstorey-drifts, absolute floor accelerations, forces and strokes of the dampers are different.