Issue 50

A. Marinelli et alii, Frattura ed Integrità Strutturale, 50 (2019) 438-450; DOI: 10.3221/IGF-ESIS.50.37 439 Cultural heritage is among the priceless and irreplaceable assets, not only of each nation, but of humanity as a whole [2]. Since ancient times, natural building stone has been employed as primary construction material for a wide range of different structures, from massive aqueducts and bridges to simple walls and columns. The rehabilitation and conservation of historic stone masonry buildings is a matter of great importance around the world, as it is related with the need to improve and extend the life of a structure for new conditions of use while protecting our cultural heritage. Scotland’s historic environment is an essential part of the country’s cultural background and its economy. Scotland has a long history of building with stone and is one of the countries with the richest legacies of traditional and historic buildings in the UK, with around 450,000 traditionally constructed buildings including castles, bridges, dwelling houses and churches [3]. Some of these are internationally iconic structures of historical and cultural heritage. The city of Edinburgh is an excellent showcase of natural building stone’s use as a construction material, being extensively utilized since the early 11th century and earning the city the alias ‘the Grey Athens of the North’ (Fig. 1). Various types of sandstone, such as Dunhouse, Corsehill and Craigleith, were easily available due to the abundance of quarries located locally in the Lothians and Fife [4]. Eventually, during the construction of the ‘New Town’ district of Edinburgh from the 18 th to the 20 th century, the local sandstone supplies became exhausted paving the way for new types of stone to be imported into the city from further afield in Britain, such as limestone, granite and dolerite. This added further depth to the architecture of the city (Fig.2a,b). Nowadays, of the roughly twenty quarries in Scotland, eight are currently producing dimensioned sandstone and six are producing flagstone (laminated, fine-grained sandstone suitable for paving). Since the conclusion of World War 1, the use of natural building stone as a primary construction material declined in place of cheaper, easier to produce materials such as concrete [5]. However, in the past thirty years, there has been a revival in the use of natural building stone, attributed to both architectural requirements and public yearning for buildings that are not just functional but also aesthetically pleasing, with the National Museum of Scotland (Fig.2c) and the Scottish Widows building being great such examples of modern structures. Still though, nowadays most projects involving natural building stones in Edinburgh are restoration projects, presenting challenges regarding diagnosis and conservation due to the variability of the mechanical and physical properties of masonry components, their complex geometry and construction techniques, the deterioration level and the lack of historical technical documentation. Design concepts for projects involving natural building stones are largely based on the ultimate strength of materials. The possibility of introducing alternative criteria on the basis of linear fracture mechanics concepts, taking into account the brittleness of the natural building stone and the presence of cracks in it, is examined for the case of two commonly used in Edinburgh such stones: the ‘Grove Whitbed’ Portland limestone and the Corsehill sandstone. At a first stage, for the Figure 1 : (a) National Gallery; (b) Royal Scottish Academy, The Mound. Figure 2 : (a) The Royal Society of Edinburgh; (b) St. Mary’s Cathedral; (c) National Museum of Scotland. (a) (b) (a) (b) (c)