Influence of design mistakes and material degradation on the collapse of a long-span RC roof in South Italy

In 2004, during ordinary maintenance work, consisting in the waterproofing of a building located in the South of Italy, the long-span (14.50 m) in situ cast reinforced concrete (RC) roof partially collapsed. The building, constructed in 1950, was in service as a cinema up to 1967 and utilized as a school up to 1985. Finally, it was a hotel up to 2000. In 2004, when the building was not in service and underwent maintenance work, it partially collapsed under the dead load. After the collapse, which involved a large portion of the roof, several beams and two columns, the Court nominated a first Official Technical Consultant in order to investigate on the causes of failure and related responsibilities. Later on, after the main responsibilities were identified, the building was repaired and the roof was reconstructed with a light steel structure. The present work is focused on the behavior of the collapsed structure considering the originally design choices, the construction details adopted and the decay of material properties including the effect of concrete and steel degradation. The influences of these aspects on the collapse was examined with particular emphasis on concrete carbonation, steel bar corrosion and design mistakes. The lesson learned from the case study could help professional engineers in being aware of the main peculiarities and structural deficiencies of structural systems affected by material degradation and the importance of in situ periodical checks and monitoring during the life of structures. Finally, the design of a new steel roof as retrofitting solution for collapsed roof was shown.