Wind induced loads on the monumental roof structure of the XII Century ‘Palazzo della Ragione’ in Padova

The Palazzo della Ragione is a historical building in the centre of the city of Padova, in northern Italy. It is of outstanding artistic importance, and is also extremely interesting from the engineering point of view mainly owing to its roof structure. In fact, the peculiarity of the roof consists in its quite unusual & pronounced height above the building crown & in the cross-section with a gothic-arch profile that strongly reminds to a boat hull. The ground plan of the roof is roughly rhomboidal 35x85 square metres). A first, ordinary roof was built in the year 1219, and it was re-shaped in 1306, after the example of an Indian pavilion. During February 1420, the roof structure was completely destroyed by fire, and eventually on August 17th, 1756, a violent windstorm blew away almost the entire roof, thus pointing out a wind sensitive shape of the roof (even considering the violence of the storm). After its complete restoration, nowadays the need is felt of a complete structural check-up of the vaulted roof to identify the possible strengthening countermeasures (if necessary), starting with the identification of the actual wind induced loads on the roof structure. Owing to the complex shape of the roof, an experimental campaign in Boundary Layer Wind Tunnel has been set up, whose main steps were: a) the correct estimation of the local roughness of downtown Padova, b) the reproduction of the actual wind velocity profile, and c) the determination of dynamic wind pressures on the roof structures. The analyses gave hints on the possible reasons for the disastrous collapse of 1756.