Critical aspects and stress redistribution in historical multi-leaf masonry walls

Massive masonry structures, like historical high towers and large pillars of churches, can be subjected to critical static situation, due to heavy persistent compressive stress, associated with vertical dead load. In the case of multi-leaf walls, the assessment can be difficult in regards to both, evaluation of the compression strength of masonry, and analysis of the state of stress. This research is motivated by the problem of the medieval bell-tower of the Church of S. Maria Assunta on Torcello Island in Venetian Lagoon; the aim is to quantify the redistribution of stress during the centuries across the wall, caused by non-uniformity of creep. Particularly, this study analyses the gradual increase of compression stress in the masonry cladding that could reach critical values. Due to little information about experimental data, long-term tests on reproduced ancient lime mortar have been started in order to define the creep behaviour of different mixtures. Another purpose is to investigate the advantages in terms of stress reduction due to partial and limited rebuilding technique (“scuci-cuci”), frequently used in the past, for the substitution of heavily damaged parts of masonry.