Proposed seismic classification of Italy and related actions

Abstract

The paper reports the results of a study conducted on the classification of Italian seismic zones. The study investigated seismic clas- sification alternatives, identifying actions to be applied to the design of new structures and to the retrofitting of existing ones for seismic compliance. The findings from the study were compared with the contents of Prime Minister's Decree 3274/03 and with the Consolidated Text of provisions arising from Decree of the President of the Republic no. 380 of 6 June 2001. An ad-hoc seismic hazard estimation, based on the latest data available in the literature, sup- ports the considerations made in the paper. Under the above Regulations, Italian municipalities are grouped into zones belonging to the same "seismic category" and the same spectral shape is used for defining the seismic action of all zones. These choices result into seismic actions that are more severe (or, in some cases, less severe) than the ones representing actual seismicity. To redress this situation, the paper suggests an alternative taking into account the specific seismicity of each municipality, so as to obtain a more homogeneous distribution of hazard levels (and of the related accepted risk) among municipalities. This goal is achieved by replacing the classification based on “seismic zones” with the defini- tion of a “municipality-specific” seismic action. The paper describes an approach to be applied to the hazard spectrum with a view to obtaining a regularised shape of the elastic spectrum. Moreover, as earthquakes have different distribution, frequency and intensity in the various zones of the country, different seismic actions should be defined for the Ultimate Limit State (ULS) and for the Damage Limit State (DLS).