Simonetta Baraccani

A Structural Analysis of the Modena Cathedral

ABSTRACT Historical monuments, by their own features and evolution over time, represent a unicum characterized by large uncertainties. With the aim of preserving cultural heritage for future generations, the assessment of the static conditions of the monuments is a crucial point. In order to perform a robust and reliable evaluation of the structural behavior and to eventually forecast possible evolution of the safety level, it is of fundamental importance to carry out a comprehensive study by taking into account contributions coming from different fields. The aim of this article is to present a preliminary assessment of the structural “health” of the Cathedral of Modena (Italy) making use of a multi-disciplinary multi-analysis approach, capable of providing an integrated knowledge of the monument. Different analyses (simple, but more reliable limit schematizations, and more complex, but too much sensitive to uncertainties, computer-based models) have been conducted on the global structure of the masonry fabric as well as on the local response of the single masonry walls and other significant structural elements, in order to identify the main static vulnerabilities.

Structural interpretation of data from static and dynamic structural health monitoring of monumental buildings

Structural Health Monitoring (SHM) has a crucial role in the diagnosis and conservation of historical buildings, which are typically characterized by articulated fabrics, constructed over decades using different materials and construction techniques. All these issues lead to very complex structural behaviour whose reliable assessment cannot disregard from a sound interpretation of data from SHM systems. SHM systems can be classified into (i) static systems, monitoring the long term time evolutions of specific quantities (such as amplitude of cracks, inclination of walls, relative distances, etc.) and (ii) dynamic systems, continuously monitoring the dynamic response (velocities, accelerations) in order to gather information upon overall dynamic properties such as natural frequencies, mode shapes and damping ratios. The recorded raw data need to be processed in order to distinguish eventual evolutionary trends from the seasonal and daily variations related to thermal effects. In the present work, a simple unified approach for data interpretation acquired from both static and dynamic SHM systems installed in historical buildings is presented. The approach is aimed at: (i) introducing reference quantities for interpretation of seasonal and daily variations, (ii) providing order of magnitudes of reference quantities and (iii) identifying eventual evolutionary trends which could be related to the presence of potential structural criticalities. The approach is illustrated referring to the “Two Towers” of Bologna.

Seismic Modelling of a Masonry Monument Including the Interaction of the Vaults, Longitudinal Walls and Soil

The efficient preservation of masonry monuments presents several challenges given that they are characterized by much larger uncertainties than ordinary buildings and conventional analysis tools may fail in providing a reliable characterization of their structural behavior. A complete understanding of the structural behavior of masonry monuments requires integration of historical, topographical, structural, and geotechnical information. From 2010, an interdisciplinary committee has been established to study the Cathedral of Modena, a masterpiece of Romanesque architecture in Italy. Great effort has been devoted to the assessment of the structural health of the Cathedral, revealing that the vaults are the most vulnerable components, and that the dynamic response may be significantly affected by differential soil properties at the supports. The Discrete Element Method provides a useful numerical tool to assess the dynamic behavior of masonry buildings, though previous work has been primarily focused on the structural response with less attention devoted to soil-structure interaction. In this study, a simplified modeling technique is employed to account for soil structure interaction within the DEM framework. More specifically, a specific cross section of the Cathedral, characterized by different soil properties at the supports and the absence of tie-rods, is studied. The results indicate the importance of the soil effects on the structural response.

Seismic Behavior of One-Storey Gabion-Box Walls Buildings

Gabion-boxes, made with steel wire mesh and filled with stones of appropriated size, are normally stacked up one into another to form a retaining wall. Given their reduced costs and the easy availability of their constituting materials, gabion-box walls have been extensively used in developing countries (such as Nepal) also to realize simple one-storey residential buildings. In recent years, many of these structures have been subjected to several strong earthquakes and have shown a good seismic behaviour, even if they have never been the object of a proper structural design. In the scientific literature, research studies have been developed on gabion-box walls used as retaining systems, but no investigations have been conducted on the performances of gabion-box walls buildings. In this respect, the general objective of this research work is to give a first insight into the static and seismic behaviour of such gabion-box walls buildings through analytical considerations and numerical models. In detail, with reference to a typical 5 m x 5 m plan model, this paper investigates the in-plane and out-of-plane seismic responses of its constituting walls, by means of simple analytical interpretations and Discrete Element Method (DEM) numerical simulations. Even if this study should be considered as a starting point and even if the fundamental cellular behaviour of the 3-dimensional structure has not been fully taken into account, some criticalities have been disclosed and the order of magnitude of the seismic activation load multipliers has been estimated. The out-of-plane collapse mechanism is characterised by multiplier around 0.15, whilst the in-plane mechanism multiplier depends on the position of the door in the single wall (0.10 – 0.20), but can be easily increased with lintel beams placement. The results are based on the assumptions taken by several authors and have not been verified with experimental tests. Nevertheless, some practical suggestions (basically in terms of spacing and construction details, such as vertical connectors and reinforcing steel knots) can be derived to improve the construction in order to ensure a better seismic behaviour.

Structural Strengthening of the Portico of the Santa Maria Dei Servi Church in Bologna

The porticoes, together with medieval masonry towers, are the architectural element which mainly characterizes the city of Bologna, northern Italy. These porticoes, which extend all inside the city centre for a total length of almost 40 kilometres, have a high artistic and cultural relevance at the point that they are candidates as “Unesco World Heritage Site”. One of portico of highest heritage value is that next to the church of Santa Maria dei Servi, which is suffering important structural pathologies requiring urgent strengthening interventions. The ones strictly necessary to preserve the stability have been already implemented. It is known that for historical constructions appropriate strategies of interventions are to be adopted with special attention in the aspects related to the compatibility, durability, integrity of the original configuration. The aim of this paper is to identify the main criticalities and priorities of interventions. Based on the identified criticalities and priorities possible strategies of interventions are finally identified. A possible cause of the actual bad state of conservation could be related to the continues vibrations induced by the traffic. For this reason, measurements noises have been recently conducted by the Italian National Institute of Geophysics and Volcanology (INGV) in order to quantify their influence of the stress levels of the columns of the portico.

Reference Quantities and Values for a Possible Interpretation of the Data Acquired from Monitoring System of Historical Buildings

Preserving historic buildings is essential in the safeguard of the cultural heritage of any country. The need to carry out structural analyses by means of non-destructive methods has made structural monitoring ever more widespread in the diagnosis and control of historic buildings. The aim of this study is to introduce a standardized approach for the analysis of the data acquired from a monitoring system of historic buildings. This approach is based on the definition of specific reference quantities (extrapolated from the recorded time series) able to characterize the main features of the structural response and the preliminary identification of the order of magnitudes of these quantities. It is assumed that the recorded time series can be decomposed into two components: a periodical one depending on with the natural forces acting on the building and an unknown one related to the variation of the state of the structure. Exploiting the properties of periodic functions, one may identify these reference quantities, which are based on the year and the day variability and allow to monitor the evolution of the phenomena under observation. These reference quantities may be collected in a database and may become fundamental for comparing the response of similar buildings. This approach has been applied to the data obtained from the monitoring systems of two important Italian monuments: the Cathedral of Modena and the “Two Towers” of Bologna.