Excessive Deflection in Long-Span Timber Beams of a Historical Building in the South of Italy: Analysis and Retrofitting Design

In 2018, under service conditions, excessive deflections were observed in the long-span timber beams of the first floor of the former Sant’Elisabetta Monastery in Palermo (Italy). The building was constructed in the 16th century. Over the years, it underwent several modifications and, finally, in 1900, became a barrack. In the middle of the twentieth century, the monastery was submitted to maintenance works consisting of the reconstruction of the first floor with timber beams and the reconstruction of the roof with timber trusses. In the summer of 2018, anomalous and excessive deflections of the primary beams on the first floor approaching $1/50$th of the span were observed, raising concerns. Therefore, an experimental investigation was carried out to establish the causes of the damage and to identify a retrofitting design. In this work, extensive experimental research was carried out to characterize the timber materials and structural members through static and dynamic tests. The results obtained represent support of a strengthening design for the timber beams, and the design’s main execution phases are described in this paper. The lesson learned from the case study could help professional engineers be aware of the main peculiarities and deficiencies of structural systems affected by material degradation—in this case, mainly depending on construction mistakes—and the importance of in situ periodical checks during the useful life of structures.