On-site integrated non-destructive diagnosis of historic timber elements: the case of the roof of Palazzo D’Accursio, Bologna

D’Accursio palace in Bologna, Italy, is the historic town hall of the city. Starting from the 13th C. its actual structure is the result of several modifications, renovations and expansions carried out until the end of the 19th C. The building is considered a monument of high historical architectural value, hosting relevant museum collections on the 2nd floor where the Coat-of-Arms Hall with its decorations and double height is the most representative room. Recent renovation works carried out to the roof of this room were made necessary from the long-time rain water infiltrations causing damage also to the ceiling and wall painted surfaces. During the substitution of the existing roof covering mantle and of all secondary timber elements, promoted by the city technical offices with the aim to improve also the thermic insulation, scaffoldings and goods lift were especially mounted. Thus, it was possible to access the roof level and inspect the 6 trusses and rafters left in place. Due to time constraints, after geometric survey of the trusses and photographic documentation, only selected elements were tested by integrated non-destructive testing approach. After visual inspection, besides drilling penetration resistance, acoustic and electromagnetic inspection methods were applied. Sonic transmission tests along the trusses’ tie-beams, IR thermography investigations of elements joints and high-frequency GPR radar survey were carried out to evaluate the presence of defects, the extension of decay areas due to moisture, the positions of knots and cracks on the timber trusses. The results of this testing would aid to assess the health-state conditions of this historic roof structure. This paper presents selected results from this innovative diagnostic campaign presenting examples and discussing operational and environmental constraints affecting the investigations.