Free-Field Seismic Response Analysis: The Piazza dei Miracoli in Pisa Case Study

Free-Field Seismic Response Analysis: The Piazza dei Miracoli in Pisa Case Study

Andrea Angina (Department of Civil and Industrial Engineering, University of Pisa, Pisa, Italy), Andrea Steri (Department of Civil and Industrial Engineering, University of Pisa, Pisa, Italy), Stefano Stacul (Department of Civil and Industrial Engineering, University of Pisa, Pisa, Italy) and Diego Lo Presti (Department of Civil and Industrial Engineering, University of Pisa, Pisa, Italy)
Copyright: © 2018 |Pages: 21
DOI: 10.4018/IJGEE.2018010101

Abstract

This paper shows the results of free-field seismic response analyses (SRA), that were performed for the subsoil conditions of Piazza dei Miracoli in Pisa. The site investigation and in particular the shear wave velocity profile is extended down to 120 m below the ground level. One-dimensional SRA were carried out by using three computer codes, EERA, STRATA and ONDA. The first two codes perform the analyses in the frequency domain considering a linear-equivalent soil model. ONDA analyses the problem in the time domain assuming a true non-linear soil behaviour. In particular, the Ramberg-Osgood constitutive model, coupled with a modified Masing criterion was assumed. The computed elastic response spectra were compared to those prescribed by the Italian Building Code, which represents the Italian implementation of Eurocodes. Some details concerning the response spectra prescribed by Italian Building Code are also given.
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Introduction

The stabilisation works of the Leaning Tower of Pisa ended in 2001 (Jamiolkowski, 2001; Burland et al., 2000, 2003). The Tower was re-opened to visitors, after a closing period long at least one decade. After re-opening, works related with the material restoration of the Tower, some recovery activities for the monuments located in Piazza dei Miracoli and the monitoring of the Tower displacements were carried out (Burland et al., 2009; Squeglia & Bentivoglio, 2015).

More recently, after the seismic events that hit the regions of Central Italy, especially the Emilia Romagna earthquake in 2012 (Lo Presti et al., 2013; Fioravante et al., 2013), the interest about the seismic response of the Leaning Tower has become relevant for the Italian geotechnical community.

It is well known that the analysis of the complex dynamic soil-foundation-superstructure interaction can be simplified studying separately (Kramer, 1996):

  • 1.

    The free-field response;

  • 2.

    The kinematic interaction;

  • 3.

    The inertial interaction.

The first step provides an estimate of the seismic motion variation during the propagation of the seismic waves from the bedrock to the ground surface, in terms of amplitude and frequency content, due to the presence of a weaker overlaying soil deposit. Such an analysis neglects the influence of both the foundation and the superstructure.

In this work, the analyses were carried out assuming a one-dimensional geometry, the presence of vertically propagating shear waves (SH-waves) and as constitutive models for the soil deposit: a linear-equivalent and a non-linear model (Ramberg-Osgood model).

The analyses were performed with a linear-equivalent approach using the computer codes EERA (Bardet et al., 2000) and STRATA (Kottke & Rathje, 2010) and with a true non-linear analysis method using the code ONDA (Lo Presti et al., 2006).

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