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SUMMARYThis paper presents a procedure to identify an optimal retro"tting strategy for electric power networks (EPN) subjected to seismic events. The optimization consists of the minimization, under economic constraints, of the probability of power cut-o! at the nodes where electric energy is most needed in the post-earthquake situation; these nodes are referred to as critical nodes. The EPN model used herein has been presented earlier and is brie#y reviewed in the text. The method to individuate the critical nodes, based upon the value of an index proposed in this study, is presented "rst; then the optimization procedure to select which elements of the EPN to upgrade is examined based upon a standard reliability study. Its e!ectiveness is tested against routinely used upgrading schemes for an existing EPN (the one of Sicily in Italy). It is shown that the optimization procedure is e!ective and leads to a signi"cant saving of economic resources.

SUMMARYThe aim of this study is to develop design criteria, which account for the e ects of earthquakes spatial variability. The two simplest forms of this problem are dealt with: di erential ground displacements and di erential structural displacements, for points and structures separated in space. The structures considered are linear elastic single degree of freedom oscillators. These problems may seem trivial, but some of the codes considered appear improvable on this aspect.First, the mathematical model is set up using basic random vibration theory and the code provisions critically examined. Then, the sensitivity of the ground and structural di erential response is assessed. The di erential displacements can be mathematically expressed in a straightforward fashion, both for the ground and the structures. These expressions are simple enough to be used as design rules.Comparison with the European and Italian Civil Protection codes shows that these can be improved on this aspect; and, for this reason, the Italian draft code for bridges has been mainly drafted following the results of this study.

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