Empirical estimate of fundamental frequencies and damping for Italian buildings

Abstract

SUMMARYThe 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 abovementioned 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.

Evaluation and considerations about fundamental periods of damaged reinforced concrete buildings

“…We first explore a possible separation of more or less damaged buildings, dividing the database to consider the different damage levels surveyed. The period vs. height data of the buildings with DL1 are very close to RC Italian and European relationships experimentally estimated by Gallipoli et al (2009) and Gallipoli et al (2010) for undamaged buildings. The first damage level (DL1) is defined in EMS 98 (Gruenthal, 1998) as negligibleto-slight damage (only non-structural damage) with fine cracks in plaster over frame members or in walls at their base, and fine cracks in partitions and infills.…”

“…Moreover, in a noisy environment with ongoing restoration and demolitions, HVSR has the same target in the building and in the soil: that of separating the true shear response of the investigated object from the propagating noise that can mask the true eigenfrequencies. In previous works, HVSR has proved to be a reliable proxy of SSR to estimate fundamental frequencies, as demonstrated on a large set of Italian buildings by Gallipoli et al (2009), provided that the measurement points are carefully selected to avoid membrane modes of the floors and other possible problems as described in the appendix of the paper by Gallipoli et al (2010). Table 2 reports the analysis results for each building, with age classes, damage levels and building height.…”

“…The use of a fast procedure and a portable instrument allows studying a large number of buildings during an earthquake-related emergency. Gallipoli et al (2009Gallipoli et al ( , 2010 and Ditommaso et al (2010Ditommaso et al ( , 2012) have compared several techniques for structural dynamic identification: ambient noise vibrations are very useful for the characterization of the fundamental frequency and the related modal shape (if more than one station has been used). In this work the frequencies have been estimated using ambient noise recordings by means of a portable three-directional tromometer (Micromed Tromino).…”

“…On the contrary, the theoretical equation provided by the codes returns periods that are an over-estimation even when this level of damage is observed. This disagreement has to be considered taking into account the construction practices used in each country, with the need to perform a similar investigation and to define a relationship based on typical Italian and European buildings, as showed in previous works by Gallipoli et al (2009Gallipoli et al ( , 2010, Guler et al (2008), and Oliveira et al (2010) for undamaged RC buildings. …”

Estimation of the Period of Vibration of Existing Egypt RC Building Based on Experimental Data and Numerical Results Under the Effect of Soil-Structure Interaction

“…In the last years many experimental and numerical studies as well as many research projects have been carried out in order to define in a simplified way the fundamental period of Reinforced Concrete buildings, Gallipoli et al [1], Crowley and Pinho [2], Al-Nimry et al [3]. Particularly, empirical relationships between the height of a building type and its fundamental period of vibration have been sought, as they can be very useful in many applications.…”