Natural Fibers for Out-of-Plane Strengthening Interventions of Unreinforced Masonry Buildings in Aggregate Configuration

Most of the Italian historical centers are composed of unreinforced masonry (URM) buildings arranged in aggregate configurations. Past and recent seismic events have underlined the high vulnerability of these buildings especially towards out-of-plane mechanisms. In order to reduce their vulnerability, the use of strengthening interventions based on fiber reinforced composite materials has become widespread in the last years. More recently, strengthening systems using natural fibers have been the object of experimental tests since they represent an innovative environmentally sustainable solution. The aim of this paper is to numerically analyze the feasibility of strengthening systems made of natural fibers embedded into cementitious matrices to prevent the out-of-plane mechanisms of perimeter façades belonging to masonry buildings in aggregate configurations. For this purpose, numerical analyses based on a macro-modeling approach for out-of-plane mechanisms are performed by considering the influence of adjacent structural units and the presence of strengthening systems made of natural fibers. Both aspects have been analyzed in detail and taken into account by introducing in the equation governing the problem both the friction acting between adjacent walls of building units, when in aggregate, and the contribution of the strengthening system. A building case study forming part of an aggregate of an Italian historical center has been considered for the development of the numerical analyses.