Seismic hazard analysis of SDOF modelled power systems

In a country like Italy, directly affected by seismic phenomena, the assessment of the seismic hazard in the entire territory plays a very important role, in order to both evaluate the seismic vulnerability of built power lines and power facilities and optimize the design of new construc-tions. In order to carefully assess their seismic vulnerability, it is of crucial importance the pre-cise statistic determination of the seismic input. For this purpose two procedures for the Probabilistic Seismic Hazard Analysis (PSHA), i.e. the probability functions (CDF: cumulative distribution function and PDF: probability density func-tion) of a selected ground motion parameter (e.g., peak ground acceleration, peak ground veloc-ity, peak ground displacement, spectral acceleration, …) at a specific site, over a given observa-tion time, are analytically developed and elucidated. Both procedures are developed according to Cornell’s widely upheld approach (1968). The first procedure is characterized by the treat-ment of the distance R from the epicentre to the site as a continuous random variable, while the other treats R as a discrete variable. Both procedures lead to closed-form analytical expressions for the PDF and CDF of the selected ground motion parameter and its prediction. The paper also presents illustrative examples of application of the two procedures to the Italian territory for the determination of the probability functions of the peak ground horizontal acceleration for se-lected Italian sites. The results here obtained are extremely useful for the evaluation of seismic risk and the seismic design of components of the three functional zones (generation, transmission and distribution facilities) of power systems. As these power systems components are easy to be modeled dy-namically, the results of numerical simulations based upon dynamic inputs characterized by a selected ground motion parameter computed with the proposed above methodology may pro-vide results which are extremely reliable. The full knowledge of the relationship between the probability and the seismic action at a site is fundamental for both assessment of seismic reliability/hazard of generation, transmission and distribution facilities and for the careful design of new power systems structures (as targeted probability of survival to earthquake inputs can be carefully achieved).