Seismic Retrofit of a Precast RC School Building with External BRBs in Northern Italy

Precast RC structures have been widely used in Italy during past 60 years and mainly adopted to host industrial and commercial activities, as well as school buildings, such as the “Ercole I d’Este” in Ferrara. For these structures, quite common features are poor connections between structural elements, along with limited shear strength and flexural ductility of columns. Many of them were designed for gravity loads only, since past regulations did not imposed earthquake loads application for the whole Italian territory. Recent seismic events have proved how much these structures are prone to premature and fragile collapse, as observed during the 2012 Emilia Earthquakes when they caused several casualties, injured people, and displaced. This study presents the application of Buckling Restrained Braces (BRBs) as advanced retrofit solution for a sustainable upgrading of precast RC structures seismic performances. BRBs are implemented to add significant damping to traditional external seismic steel bracings, and seismic forces are transferred to external bracings thanks to a proper floor and roof reinforcement. Direct displacement-based design is applied to design BRBs, optimizing their sizing and plan position. BRBs effectiveness on the RC precast structure upgrading has been investigated using nonlinear time history analysis. The designed retrofit solution provides a global improvement of the seismic performance of the building to prevent any structural and nonstructural damage with sustainable costs. The major benefit of BRBs application respect to traditional braces is the reduction of external bracing and their foundations which leads to significant savings.