THE ROLE OF THE MASONRY QUALITY EVALUATION IN HISTORIC CONSTRUCTIONS IN SEISMIC AREA

The worst structural defect of a masonry wall can be the lack of monolithic behaviour and this can happen in case of poor quality and morphology, for instance when the wall is made by multiple leaves even well ordered but not mutually connected. In case of a seismic event, external forces act in horizontal direction, causing the wall to become more vulnerable with separation of the leaves. Therefore it’s important to verify from the beginning the masonry quality in an existing building and to carry out properly this work. The present Italian seismic code (NTC 14.01.2008 and annexes) requires, for existing buildings, different levels of knowledge; the lowest, named LC1, requires only to classify the masonry among the typologies reported in a table and allows the use of the mechanical parameters in a range of values related to each typology. Serious mistakes can be made in the structural evaluation of a historic stone masonry if the definition of the masonry typology is incorrect. In several cases a masonry texture can appear externally good and regular while the cross section is poor with non-connected multiple leaves, or, on the contrary, the masonry texture appears to be irregular from the prospect with small irregular stones of different dimensions while the cross section shows a well interlocked masonry with long stones used as connection among the leaves. Several parameters may be thus important to be determined in order to evaluate properly a masonry. A methodology to define essential parameters and consequently the stone masonry quality, especially in seismic areas, is presented in this paper.