Seismic upgrade of masonry buildings by using innovative active FRP-Technique

Innovative materials such as Fiber Reinforced Polymer (FRP) have been widely used for the seismic upgrade and reparation for a couple of decades. This testifies the effectiveness of such techniques, especially when they apply to vulnerable masonry structures. In this study, the seismic upgrade of a large building, used as a theatre in the south of Italy, is illustrated. After a seismic analysis based on the study of the collapse mechanisms of the masonry walls, a strengthening program was individuated and successfully applied in-situ. The analysis was conducted with reference to the local mechanisms that can be activated by the seismic acceleration in the considered site. The kinematic analysis was performed as linear and non-linear. In the first case, the control parameter is represented by the minimum value of the seismic acceleration that can be supported by the excited sub-structure. When a non-linear analysis is implemented, the controlling parameter is the maximum displacement that guarantees the ultimate equilibrium configuration. It will be shown how the linear analysis may be more conservative with respect the non-linear one. Once the seismic vulnerability was quantified in terms of acceleration and displacement, an innovative strengthening system was designed. The seismic upgrade was evaluated by the comparison with respect the un-reinforced state of the construction. In order to avoid out of plain failure mechanisms, an active confinement was designed by using pre-tensioned carbon-aramid fiber wires, anchored trough steel plates to the masonry substrate. Four tensioned CFRP-AFRP (Carbon FRP – Aramid FRP) wires were placed along three sides of the building at different levels; each of them had a length of about 40 meters. The installation of the wires, the anchoring system and the tensioning procedure will be illustrated in the paper. The choice of composite materials allowed this type of innovative technique, by guaranteeing a high durability, speed of installation and safe operations in elevation. The conclusions will show how the designed strengthening technique is able to preserve the stability of the structure and improve its performance in case of seismic events, with no impact on the architectural aesthetics of the building. The intervention can also be considered removable according to the ISCARSAH’s recommendations.