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Historic metal tie-rods

Chiara Calderini 1 Philippe Dillmann 2, 3
2 LAPA - UMR 3685 - Laboratoire Archéomatériaux et Prévision de l'Altération
NIMBE UMR 3685 - Nanosciences et Innovation pour les Matériaux, la Biomédecine et l'Energie (ex SIS2M)
3 IRAMAT - LMC - IRAMAT - Laboratoire Métallurgies et Cultures
IRAMAT - Institut de Recherches sur les Archéomatériaux
Abstract : Metal tie-rods are relevant structural elements in heritage masonry buildings. They contribute to guaranteeing an efficient connection between walls and play a decisive role in the control of horizontal thrusts produced by static loads acting on vaults and arches or earthquake–induced dynamic loads related to seismic actions. Historically, metal tie-rods were often installed in historic buildings during the construction stage. However, they were also inserted in buildings in a subsequent phase, if it was necessary to modify a structure (superelevations, building aggregations etc….), increment the load (use variation), or repair and strengthen a building after an earthquake (as occurred after many historical Italian earthquakes). Still today, the insertion of metal tie-rods is one of the most widespread technique adopted to reinforce historic masonry buildings, in particular in seismic-prone areas. Despite this large use and the crucial role of tie-rods in historic buildings, few researches in the past focused on the historical and technical characteristics of these structural elements. On the one side, there are only few and sparse research on the way in which they were produced (ironmaking processes), assembled and set (position, size and shape, linking systems, etc) as well as on the material they are made of (from wrought iron to mild steel) and his heterogeneity. Some researches based on archaeological science methods were performed in France for medieval gothic monuments aiming on the one hand to locate and date the use of iron in the monuments, on the other hand to decipher their production processes. Nevertheless, these researches were limited to the French territory and mainly the North of the country. They have provided a large amount of information on the microstructure of materials but, on the other hand, very little information on their mechanical behavior. Thus, if we consider the various aspects that have just been mentioned, there is a serious lack of published research for territories other than France and other historical periods. Besides, due to the significant heterogeneity of these old materials (variable carbon contents, presence of second phase particles, etc.), whatever the periods, it is necessary to multiply the analyses of the mechanical behaviour of these objects. Moreover, despite the great efforts made in the last years to improve the structural models and the assessment methods of existing masonry structures, especially when subjected to seismic loadings, few researches were focused on the mechanical behaviour of tie-rods and on their role in the structural response of the building. Most of this studies focused on the design of new tie-rods, instead of on the assessment of existing ones. Studies on historic elements concerned mainly their response under static loads and were based on linear elastic or elastic-perfectly plastic models. In this framework, the evaluation of the mean permanent stress level (or pre-stress) of the ties has been one of the main goal of the researchers. For this reasons, historic metallic tie-rods are usually described through very simplified models, reducing them to steel strings whose elastic stiffness and strength are derived from modern steel or from experimental tests performed on wrought iron elements of the 19th century. The present Special Issue of the International Journal of Architectural Heritage aims at filling a gap on metal tie-rods, providing an interdisciplinary overview of the most recent researches. The Special Issue includes 14 high-quality articles authored by international experts. The contributions are from different fields of expertise: History of technology, Building Archaeology, Conservation, Structural Engineering, Chemistry and Metallurgy. The following topics and issues are covered in this Special Issue: historical aspects technical features of ancient tie-rods material characterization; structural models in the static and dynamic field design of innovative ties The historical aspects are a key first step to understand the way tie rods were used in the ancient times. Again, some studies were published about that aspect but are very limited and did not concern an international audience as the one of the present journal. The study of the technical characteristics of tie-rods is a relevant non only because of documentary interest, but also because, the systems of connections and the technical details of these elements may influence their overall mechanical response. The mechanical characterization of the material is the first step to provide reliable parameters and mechanical models and to outline proper inspection techniques to assess the integrity and the structural safety of tie-rods. The definition of reliable structural models for tie-rods aims at improving the overall modelling of masonry structures and, thus, their structural assessment. Moreover, they may improve the design of new tie-rods, pushing towards innovation solutions. Finally, the design of innovative ties may improve the conservation and safety of historic buildings. We hope that the present Special Issue will contribute with new knowledge to further advances in the field of safety and conservation of architectural heritage, as well as to foster interdisciplinary research and collaboration among scientists, stakeholders and all practitioners involved in their preservation. We are very grateful to the Editors of the journal, Professors Paulo Lourenço and Pere Roca, for having supported and promoted this initiative. We would like to thank all the authors of the articles, as well as the peer reviewers, who have enthusiastically accepted our invitation to contribute to the Special Issue, and have provided significant insight in the topic to the readership of the International Journal of Architectural Heritage.
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Submitted on : Monday, December 9, 2019 - 8:03:27 PM
Last modification on : Thursday, April 2, 2020 - 10:56:02 AM

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Chiara Calderini, Philippe Dillmann. Historic metal tie-rods. International Journal of Architectural Heritage, Taylor & Francis, 2019, 13 (3), pp.315-316. ⟨10.1080/15583058.2019.1603745⟩. ⟨cea-02401234⟩



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