Sviluppo di nuovi materiali, modelli e tecniche innovative per la conservazione e il rafforzamento sismico del patrimonio edilizio monumentale storico

Historically, masonry structures have exhibited, despite the intrinsic fragility of the material, extraordinary stability withstanding the effects of aging, human settlements, and natural elements over the centuries. This has led to the thinking that such structures would be eternal. However, most architectural and artistic heritage, such as castles, churches, monuments, lighthouses, mosques, arch bridges, vaults, and domes have been destroyed. Each year, we witness the further collapse of remaining historic masonry structures. In the last decade, there has been a growing demand for protecting heritage structures around the world. This demand reflects humanity’s deep awareness, responsibility, and necessity to maintain the existing architectural heritage and to pass it on to future generations. Furthermore, restoration initiatives have increased, in part, because of new technologies that produce new materials and strengthening systems. The development of a fiber-based strengthening system began in the 1960s, when the potential for adding steel fibers to enhance the ductility of concrete material was recognized. However, this technology has been commonly adopted for the reinforcement of masonry structures only in the last decade as an alternative to traditional systems, such as mortar injections, reinforced drilling, and reinforced concrete plaster. The study of historic masonry structures, especially if coupled with a sophisticated strengthening system, is a challenging task because of the difficulties encountered in the description of the complex geometry, morphology, material heterogeneity, material properties characterization, and material variation. Despite its simple composition, masonry is characterized by a composite material that leads to a complex prediction of its mechanical behavior. The theme of the proposed research is in line with the priorities of the Beni Culturali and co-financed by the Project “2014-2020 PON”, which was approved by the Research Directorate of the Italian Ministry of Education (MIUR) and co-funded by the European Social Fund (ESF). The project was realized through the correspondence of interests between the University of L'Aquila (Italy), the industrial partner “Aquilaprem s.r.l.'” (Italy), and the research partner “Northwestern University” (U.S.A.). The project aimed to characterize the existing innovative technologies as well as to identify new material for the conservation and development of the vast historical and architectural heritage that nowadays are particularly vulnerable to the environmental actions. In particular, the development of a new type of natural hydraulic lime mortar, reinforced by short fibers randomly arranged in the mortar matrix, was performed. Both experimental tests and numerical simulations were detailed discussed in the thesis. For the latter case, a sophisticated numerical framework, the so-called Lattice Discrete Particle Model, was proposed for the first time to stone masonry aiming to capture fracture, damage localization, and frictional shearing, occurring at weak locations in the internal material structure that coincide with interfaces among particles. Indeed, numerical continuum-based models, which homogenize material behavior, are inherently limited in capturing the mesoscale interactions, fracture propagation, and damage evolution of quasi-brittle materials.