174 Int. J. Earthquake and Impact Engineering, Vol. 1, Nos. 1/2, 2016 Copyright © 2016 Inderscience Enterprises Ltd. Refractive index model to determine the vulnerability curves for different building typologies Filomena Galizia* Dipartimento di Strutture per l’Ingegneria e l’Architettura, DiSt, Università di Napoli ‘Federico II’, via Forno Vecchio n. 36, 80134 Napoli, Italy Fax: +39-081-2538989 Email: fgalizia@unina.it *Corresponding author Alberto Fiorenza Dipartimento di Architettura, DiARC, Università di Napoli ‘Federico II’, via Monteoliveto, 3 – 80134 Napoli, Italy Fax: +39-081-2538909 Email: fiorenza@unina.it Abstract: In this paper, with reference to an analysis of seismic vulnerability on a territorial scale, we propose a new model for determining the damage in terms of a mean damage grade of a probabilistic nature. The theoretical approach is based on a behavioural analogy between a building and a particle in a dielectric, subjected respectively to an earthquake and a sinusoidal electric field: both phenomena are characterised by a critical value, and both phenomena obey the same rule when the relevant parameters are close to the critical value. We develop, in fact, a new expression for the vulnerability curves, simpler with respect to the existing one, and confirmed by data given in literature. This paper contributes to the development of a methodological process for estimating the degree of average damage in order to achieve results that can be used for preventive purposes. Keywords: refractive index model; vulnerability curves; mean damage grade; preventive purpose; damage estimate; seismic vulnerability; ordinary buildings; damage scenarios. Reference to this paper should be made as follows: Galizia, F. and Fiorenza, A. (2016) ‘Refractive index model to determine the vulnerability curves for different building typologies’, Int. J. Earthquake and Impact Engineering, Vol. 1, Nos. 1/2, pp.174–198. Biographical notes: Filomena Galizia received her PhD in Conservation of Architectural Heritage of the Facoltà di Architettura at the Università di Napoli ‘Federico II’ where she carries on teaching activities in Dipartimento di Strutture per l’Ingegneria e l’Architettura. She is the co-author of numerous papers published in national and international conference proceedings. Her field of research is primarily aimed at the seismic vulnerability of the buildings, with particular attention to masonry buildings, seismic risk and mechanical construction masonry with the aim of introducing innovative aspects in the analysis methods and in the modelling of structural behaviour.