In-Situ Static and Dynamic Testing and Numerical Modelling of the Dome of the Siena Cathedral (Italy)

1. Introduction

Modern societies consider the preservation of cultural heritage and passing it on to future generations a major issue as its conservation is an historical and cultural process as well as an economic source of wealth (Fioravanti & Mecca, 2011). From a social point of view the preservation of cultural heritage, ranging from local to European level, contributes to consolidating a collective memory and a European identity that creates a sense of belonging in EU citizens. From an economic point of view, especially in contexts where tourism is becoming a major industry, accessibility to cultural heritage significantly contributes to the community’s development (Bowitz & Ibenholt, 2009). From an engineering point of view, with specific reference to monumental heritage, preservation calls for an interconnected series of operations aimed at obtaining a satisfactory broad-spectrum knowledge level of the building where traditional in-situ investigations must be performed in parallel with advanced numerical analyses (Romera et al., 2008a; Romera et al., 2008b). A constant comparison between experimental and numerical results, together with an historical survey, allows to identify the monument’s structural behaviour (both under static and seismic conditions) and to assess the causes of eventual existing damages. Furthermore, the knowledge of the actual structural behaviour of the monumental building allows, if needed, to correctly design the strengthening works, and to avoid invasive retrofitting (frequently proposed in the past for several buildings) (Blasi & Coïsson, 2006; ICOMOS, 2001). In general, the diagnostic activity on a historic building consists of a series of accomplishments that can be summarized as follows:

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  Geometric and topographic surveys, identification of main constructive steps (through the analysis of historical documents) and damage survey including its evolution over time;

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  Assessment of the actual damage (if existing), through essays and surveys defining the variables that characterize the structural behaviour of the structure;

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  Measurement and interpretation of existing stresses in some significant areas of the structure (by means of static tests) and identification of the monument’s dynamic behaviour;

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  Development of numerical models (of gradually increasing complexity) capable of reproducing the experimental evidence;

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  Numerical simulation of the structural response with respect to several load conditions (i.e. vibrations induced by traffic, horizontal movements induced by earthquakes, etc.) that could affect the monumental building.

The above listed sequence of activities cannot be taken as a unidirectional vertical path. The structural investigation of a monumental building consists of an iterative approach where the typology and extension of the experimental tests must be combined with the results of numerical models of the building that are iteratively updated (Bartoli & Betti, 2013).