Some considerations on performance-based seismic design

In the last years, a substantial change has been brought in the vision of the design objectives of an engineered facility: from the need to ensure its resistance at a minimum cost in a deterministic context, to the more recent design approaches aimed at mini-mizing the total, probabilistically defined, "cost" throughout the facility lifetime (or, even better, at maximizing its "utility"). To pursue such an approach in full rigour would require solving an enormous number of problems with financial, social, ethical, and even aesthetic implications. Therefore, for practical applications, the "optimization" approach can only be tackled by simplifying the general problem, reducing the number and improving the definition of its components. The most rational way of tackling the risks of engineered facilities and infrastructures, due to natural and/or man-made phenomena, and their reduction seems to be the Performance-Based Design PBD (or, better, Performance-Based Engineering). This approach requires the satisfaction of the relevant performance requirements with a sufficiently high prob-ability throughout the lifetime of the facility. The paper will discuss the general framework of PBD, with specific reference to seismic engineering, and illustrate two approaches to Performance-based Seismic Design PBSD. It can be concluded that PBSD is a potentially very powerful approach for mitigating the losses due to seismic hazards, that however is still under development.