Application of DEM to Historic Masonries, Two Case-Studies in Portugal and Italy: Aguas Livres Aqueduct and Arch-Tympana of a Church

Application of DEM to Historic Masonries, Two Case-Studies in Portugal and Italy: Aguas Livres Aqueduct and Arch-Tympana of a Church

Alberto Drei (Technical University of Milan, Italy), Gabriele Milani (Technical University of Milan, Italy) and Gabriela Sincraian (Vancouver Coastal Health, Canada)
DOI: 10.4018/978-1-5225-0231-9.ch013
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Two engineering applications of the Distinct Element Method to the analysis of historic masonries are presented. In particular, the commercial software UDEC, which implements DEM in a variety of engineering problems, is here used to analyze the Águas Livres aqueduct in Lisbon (Portugal) and multi-leaf masonry arch-tympana carrying systems of a basilica in Como (Italy). When dealing with the aqueduct, the most important portion of the structure is modeled and loaded with some accelerograms to evaluate its seismic vulnerability as well as the most critical zones. The second example analyzes the arch-tympana carrying system of a church in Italy. They present an unusual building technology, relying into a multiple-leaf arch, and a tympanum, made by a mixture of bad quality mortar and small stones. Again the structure is discretized into distinct elements and the load carrying capacity under dynamic excitation is evaluated, discussing the role played by the infill.
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A major part of the worldwide built stock is formed by old masonry buildings, made of stone or brick blocks. They also constitute the old urban nuclei in many towns, especially in Europe, and many of them are relevant part of the architectural and historical heritage. As they are representative of an earlier building tradition, there is a strong need of preserving them for future generations. Such structures, of great cultural significance, are generally vulnerable to seismic events, which have often caused massive damage or even their destruction. Examples can be found in past earthquakes, and similarly, in recent events, earthquakes have caused extensive damage and the destruction of both monumental buildings and traditional masonry houses.

Given the urgent need to protect the built cultural heritage from destruction caused by external agents, among which, especially in southern Europe, the seismic action is probably the most threatening, the effort to understand the behavior of historical structures has significantly increased.

Despite the fact that masonry is one of the oldest building materials, the assessment of the seismic behavior of old masonry structures often lacks of a scientific background. Their seismic vulnerability cannot be inferred by means of existing codes and certified analysis methodologies as those used for today’s constructions. Special difficulties arise for these traditional structures, with structural typologies, geometry, mechanical characteristics and detailing which are very different from the ones assumed for modern structures. Moreover, as historical monuments are several centuries old, many of them have already survived important earthquakes that led to damage and changes in the mechanical behavior of the materials, expressed by stiffness degradation and overall weakening. The analysis of their behavior under dynamic loading is essential for their safety assessment and the eventual application of retrofitting systems. The low tensile strength of the masonry components and its discontinuous nature are features that dominate the complex mechanical behavior displayed by this material, non-linear in essence. These unreinforced blocky structures cannot be considered a continuum, but rather an assemblage of compact stone or brick elements linked by means of mortar joints. The joints constitute discontinuities between distinct bodies and can alter the response of the system, compromise its stability and introduce irreversible displacements.

The evaluation of the seismic vulnerability of such structures, as for other types of constructions, depends on a good understanding of their mechanical behavior as well as on analysis and prediction tools, namely reliable numerical simulations of their seismic response. Numerical modelling of the seismic behavior of masonry structures represents a very challenging problem due to the constitutive characteristics of the structural material and its highly physical and geometrical non-linear behavior when subjected to strong ground motions. Therefore, a numerical idealization should be capable of predicting the behavior of a masonry structure from the linear stage, through cracking and degradation until the complete loss of strength, since this is a key step towards a full understanding of the fundamental physical phenomena and the reliable assessment of the structural safety of a masonry structure.

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