ABSTRACT
The design of earthquake-resistant structures is characterized by many uncertainties that the structural designer has to face. The good behavior of a structure during a seismic attack is guaranteed by safety checks, which are required according to three levels of design approach: serviceability, damageability, and ultimate limit states. For the first two limit states, exceeding the design values of seismic actions cannot produce important effects. In contrast, as the ultimate limit state is referred to as the structural behavior near-collapse in case of severe earthquakes, the variability, dispersion, scatter, and, in general, the uncertainty in the evaluation of the design value of seismic actions seem to be the rule, not the exception. The result could be the total or partial structural collapse, which is not acceptable to the seismic design philosophy.
