Upwards-Vertical extensions of masonry built heritage for sustainable and antifragile urban densification

Urban densification represents one of the biggest universal challenges of contemporary cities: the increase of urban population requires new spaces to accommodate the growing demand for housing, working and tertiary activities. However, the land available for new constructions in highly urbanized areas is very limited. In this framework, the vertical extension of existing buildings is the most sustainable strategy and fascinating. Masonry structures, constituting a major part of the built stock in the historical city centres of several European countries, are particularly suitable for vertical addition of extra-floors, since they generally exhibit an adequate overstrength for bearing an increase of gravity loads, although seismic retrofit interventions are usually required. In this paper, starting from the case study of the historical town of Pozzuoli, in South Italy, an "antifragile" approach, based on the intermediate isolation system, is suggested to rise the height of the masonry building, while reducing the global seismic demand. For this aim, in this paper are analysed the architectural-functional and structural design issues related to a vast-scale application of vertical additions isolated on the top of existing structures. Further, the feasibility and effectiveness of the strategy are discussed, and benefits in terms of seismic performance are evaluated.