Ambient Vibrations Test for Assessment of Horizontal Diaphragms in Historic Buildings

The structural assessment of horizontal diaphragms in historic buildings turns out to be one of the most difficult aims and challenges in the field of Structural Health Monitoring (SHM). Indeed, characterising these macro-elements is important for the building structural behavior as a whole and, above all, for their horizontal stiffness role, which is very strategic with respect to vertical walls. The present research proposes a monitoring approach exclusively through ambient vibration tests (AVT) by using specific velocimeters and Operational Modal Analysis (OMA). The sensors, named tromographs, are wireless, very light, with compact design and integrated software, very easy to apply. They can be used as single stations and synchronized with similar devices. The aim of the research was to evaluate the overall reliability of this approach through the evaluation of experimental dynamic parameters, as well as the frequencies and modal shape. In detail, the first part of the investigation focused on the specific characteristics of Venetian floors. The second part is dedicated to present each floor and its specific test campaign. To better check the monitoring structural approach, the first floor is timber-made but reinforced with steel beams; the second investigated floor is entirely made of wood; the last is a combination between reinforced concrete and timber. In all cases the floors are clamped to masonry walls. The third part is dedicated to the discussion of results, both in comparison and individually, particularly with respect to the entity of the found experimental dynamic parameters. The final and conclusive part outlines the benefits and problems of the AVT-proposed methodology. Conclusions show good overall reliability of the methodology does not appear complex in process elaboration and is easy to use, although there is a critical aspect due to noise effects and an overly high sensitivity of the velocimeters.