Non-destructive monitoring of an old masonry clock tower with forced and environmental actions

The aim of the paper is to describe the non-destructive tests performed on the clock tower of the Castle of Trani (Bari, Italy). The tower is about 9 meters high and has a square plan with a side of about 3.90 meters; moreover it is built on the principal enter of the Castle and supported by a barrel vault reinforced with an arch. The tower, built in 1848, was realized in tufa masonry (Stone of Trani); nevertheless, during the years, it has undergone a series of interventions, in particular in 1979 and 1997 to consolidate the walls cores with armed injections and the vaults extrados with hood in reinforced concrete. The non-destructive monitoring was realized using specific accelerometers placed on the structure for measuring the acceleration in different points. The particular squat structure of the clock tower made the traditional monitoring, with only environmental actions, the so called only-output measurements, not so safe for determining the building modal parameters. For this reason, an electro-hydraulic shaker was ad-hoc designed and realized for applying a controlled dynamic force on the examined old masonry tower. In this paper all the phases and procedures of the experimental monitoring will be described together with a preliminary analysis of the data.