Issue 46

F. Bazzucchi et alii, Frattura ed Integrità Strutturale, 46 (2018) 400-421; DOI: 10.3221/IGF-ESIS.46.37 403 Figure 3 : Example of the deck visual inspections (a) ; damage degree results survey (b) . Annone overpass: maintenance design and load checking The collapse of the Annone overpass, Lecco, at km 42.000 along the S.S. 36 “del Lago di Como e dello Spluga”, occurred on October 18, 2016. The failure had a high impact on the Italian society since it caused the death of a car driver and several wounded. The bridge was built between the 1960 and 1962, with a Gerber scheme deployed over 4 supports (Fig. 4(a)). The central deck, 24.60 m long and 4.40 m wide, was constituted by 5 precast and prestressed I-beams. Gerber supports were 0.575 m high, with and ordinary reinforcement as shown in Fig. 4(b) and Fig. 4(c). Before the collapse, the bridge was subjected to several impacts by underlying moving vehicles [1]. This was due a non-adequate free height of the overpass (< 5 m). After these events, the saddle was repaired with rebars and CFRP installments (Fig. 5(a)). However, those interventions could not renovate the shear fracture propagated over the saddle and significant presence of humidity was often detected when inspected (Fig. 5(b)). This was mainly due to the produced misalignment in the dapped-end (2.5 cm) due to the repairs, which constituted a stagnation point for running water [2]. Figure 4 : Overview of the Annone overpass [1] (a) ; Geber support reinforcement, design (b) and investigation (c) . The collapse occurred when a 107.6 t heavy 8-axels truck went across the deck with a low moving speed (Fig. 5(c)). Once the load was carried entirely by the central beam, the external repaired dapped end corbel collapsed due to the vertical reaction established for supporting the beam. Total weight on the structure was approximately 172 t, which is 10 % higher than the maximum design load adopted equal to 155 t. However, this excess should have been overcome in the safety factor. This bridge was catalogued as category II by Italian Building Codes [3], but the safety requirements were not fulfilled by the structural properties. Investigation [1] have demonstrated that this failure was compromised by:  an initial design flaws in the dapped-end corbel that significantly reduced the ultimate load;