Comparison of two fast methods for seismic vulnerability assessment of historic centres

Italian anti-seismic legislation is often criticized, claiming that it authorizes easy demolition of damaged built heritage following an earthquake in the name of safety and profitable reconstruction, as occurred after the 2016 Central Italy earthquake. This practice obviously clashes with research in restoration. However, the response must not be limited to a mere criticism, but a willingness must emerge to pursue continuous interaction with the various actors of post-seismic management, participating in the preventive phase in the complex activities that turn around the issues of seismic vulnerability of historic centres. The widespread historical built heritage in Italy, requires the definition of fast and reliable assessment procedures that allows a large-scale evaluation of the vulnerability of historical buildings before a seismic event. Among the tools there is the experimentation of the protocol for surveying historic centres, through a form called CARTIS, coordinated by ReLUIS university consortium. It is aimed at surveying the recurring residential building types in the municipality with their possible observed vulnerabilities, without assessing their damage and so before a seismic event occurs. This is a very important occasion for historic centres, because it could have a double role: on the one hand, the intention of identifying widespread seismic vulnerabilities, elaborated in order to create damage scenarios over the entire national territory and before a seismic event occurs; on the other hand, the innovative intention, presented here, of returning to the municipal offices, in a simple and immediately usable way, the results of the detailed survey campaign, necessary to obtain a picture of the single greatest vulnerabilities within the historic centre, which require subsequent urgent in-depth investigations; this picture can be reported according to a priority scale. This fast assessment can be compared with another method, also expeditious, of constructing the fragility curves starting only from information available on the Reluis-Cartis database. The curves define the relationship between the probability of reaching a level of loss of the structural safety or a vulnerability index in function of the seismic acceleration PGA and the soil orography. The developed methodology, already calibrated on damaged buildings, is applied here to a set of historic building of the same typology in a historic center near Milan never hit by earthquakes.