The presence of secondary creep in historic masonry constructions: A hidden problem

Abstract

Top-ranked European research groups have been working for years on the problem of identifying the behaviour of load-bearing elements due to creep in historic masonry structures. All analyses carried out were performed in unexpected structural collapses, related with earthquakes or not, in several regions all around Europe. These collapses are related with the presence of appreciable size cracks, which appear more or less vertically in towers, vaults and pillars. These cracks can be easy detected through mortar before the collapse but it has been detected in previous works the presence of another crack typology in stonework masonry blocks, which has not yet been taken into consideration. This second type of cracks are difficult to detect owing to their reduced size and because they are under surface patina. In this sense, several real cases are presented where these cracks were found. In the laboratory work little sandstone samples were subjected to a cyclic load to generate cracks, with the aim to propose a method to evaluate them in situ. The proposed methodology is based on the procedures employed in the field of the quantitative metallography. This work aims to point out the probable existence of these cracks hidden under stonework masonry blocks surface, in a great number of historical constructions.