Seismic retrofitting of masonry rocking elements with composite rebars

Vulnerability of unreinforced masonry structures, characterized by an out-of-plane behaviour, represents a worthy research topic, as highlighted by recent seismic events. Different retrofitting techniques, based on the introduction of proper restraints, can improve their seismic response. In this study, the more common technique, consisting in the application of vertical steel ties, is revised considering the usage of FRP rebars. The vertical restraints, placed in a centred position, are characterized by an elastic-brittle behaviour. In order to evaluate the effectiveness of the analysed retrofitting technique, the dynamic equation of motion of the anchored rigid rocking block is numerically solved. A parametric analysis is carried out for two rocking mechanisms (two-sided or one-sided), by varying geometry of masonry walls, characteristics of the seismic input and material of the vertical restraint. The obtained results show an improvement of the element seismic capacity, with an increase of the collapse acceleration, depending on the masonry block slenderness. Furthermore, the height of the block adversely affects the strengthening effectiveness. Consequently, the examined technique appears appropriate only in case of small values of the height of the masonry element.