EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS Earthquake Engng Struct. Dyn. 2009; 38:973–988 Published online 18 December 2008 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/eqe.878 Empirical estimate of fundamental frequencies and damping for Italian buildings Maria Rosaria Gallipoli 1, 2,∗, † , Marco Mucciarelli 1 and Marco Vona 1 1 Department of Structures, Soil Dynamics and Engineering Geology, University of Basilicata, Italy 2 Institute of Methodologies for Environmental Analysis, National Council of Researches, Italy SUMMARY The aim of this work is to estimate the fundamental translational frequencies and relative damping of a large number of existing buildings, performing ambient vibration measurements. The first part of the work is devoted to the comparison of the results obtained with microtremor measurements with those obtained from earthquake recordings using four different techniques: horizontal-to-vertical spectral ratio, standard spectral ratio, non-parametric damping analysis (NonPaDAn) and half bandwidth method. We recorded local earthquakes on a five floors reinforced concrete building with a pair of accelerometers located on the ground and on top floor, and then collected microtremors at the same location of the accelerometers. The agreement between the results obtained with microtremors and earthquakes has encouraged extending ambient noise measurements to a large number of buildings. We analysed the data with the above- mentioned methods to obtain the two main translational frequencies in orthogonal directions and their relative damping for 80 buildings in the urban areas of Potenza and Senigallia (Italy). The frequencies determined with different techniques are in good agreement. We do not have the same satisfactory results for the estimates of damping: the NonPaDAn provides estimates that are less dispersed and grouped around values that appear to be more realistic. Finally, we have compared the measured frequencies with other experimental results and theoretical models. Our results confirm, as reported by previous authors, that the theoretical period–height relationships overestimate the experimental data. Copyright 2008 John Wiley & Sons, Ltd. Received 28 January 2008; Revised 17 October 2008; Accepted 24 October 2008 KEY WORDS: ambient noise; fundamental period; damping; reinforced concrete buildings ∗ Correspondence to: Maria Rosaria Gallipoli, DiSGG, Universit` a della Basilicata, Viale dell’Ateneo Lucano, 10 85100 Potenza, Italy. † E-mail: gallipoli@imaa.cnr.it Contract/grant sponsor: Civil Protection Office of the Marche Regional Government; contract/grant numbers: NATO SfP 980857, DPC-INGV S3 Copyright 2008 John Wiley & Sons, Ltd.