Guidelines for the evaluation of the load-bearing masonry quality in built heritage

Historic buildings rarely show themselves as they were to their origins, with the same shape and materials The signs of local repairs, but also modifications and expansions are reported on the building as indelible scars that need to be recognized and interpreted. It is important to read these signs, especially in load-bearing structures. One of the first steps for this study is the correct analysis and classification of the quality of the load-bearing masonry, with the help of both an accurate visual inspection and a diagnostic investigation. The classification of the correct masonry typology is now requested also by the last Italian seismic code (NTC 14.01.2008 and annexes), that supplies different mechanical parameters useful for the structural evaluation, according to the masonry 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 there is no coincidence between the visible masonry texture and the transversal cross section. There are different levels of approaching this matter, starting from a description based on a visual inspection, that can be carried out with the help of a template, till the parameters definition achieved by in situ investigation tests. Several parameters may be important to be determined in order to evaluate properly a masonry. The results of the experimental investigation (with a comparison between NDT and MDT tests) and a methodology for the analysis of the masonry quality, according to the standard suggestions for the knowledge levels, reporting all the pros and cons of all methods, are here presented.