PSI - Issue 62

Alberto Gennari Santori et al. / Procedia Structural Integrity 62 (2024) 339–346 Gennari Santori A. et al. / Structural Integrity Procedia 00 (2019) 000–000

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2. “Passigiano” viaduct description

The “Passignano” viaduct, whose design dates to the early 1980s, is spread over ten spans with separate carriageways for each direction and has a total length of 630 m. The lateral approach spans (1 and 10) are characterized by a length of 35 m each, while the remaining 8 central spans have a span of 70 m. Each girder, 140.0 m long, is supported on two piers 70.0 m apart while at the ends there are two cantilevers of 35.0 m long each (Fig. 1.a). The infrastructure is made by box girder prestressed (with post tensioned tendons made by parallel wires) concrete. The overall width of the road platform of each carriageway is 10.4 m (Fig. 1.b). The static scheme can be simplified as a continuous beam on multiple supports made up of 9 reinforced concrete piers. In the centerline of spans 3, 5, 7 and 9 there are special diagonal joints characterized by 30 Dywidag bars connecting each side of the joint (Fig. 2.a).

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Fig. 1. Extract of the longitudinal profile of the viaduct (a), And typical deck cross-section (b).

The peculiarity of the special joint is the presence of a pair of bearings spaced longitudinally and vertically tied (Fig. 2b and 2c), in order to have a "double pendulum" constraint capable of allowing relative horizontal movements between the two cantilevers, while blocking vertical movements and relative rotations. The tie rod system is composed of No. 30 Dywidag M32 bars arranged in 10 lines and three orders as shown in Fig. 7.

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Fig. 2. Special joint located on mid-span No.3-5-7-9 (a), details of the joint tie-rod system at the lower support: view from outside (b), inside (c).

3. History of viaduct surveillance activity

As part of the development of the surveillance activity, both before and after the issuing of the Italian government guidelines on the safety of existing bridges, different types of investigations were performed on the viaduct. All of them have been summarized in the flow chart illustrated in Fig. 3. From annual inspections performed at the end of the 1990s, the presence of evident vertical deformation of the deck was evaluated, alarming the managing body to carry out a topographic survey in 2001 and 2022 to quantify its extent. The results obtained in 2022 highlighted a maximum deflection concerning the level of the deck, in correspondence of spans 5 and 7 equal to approximately 29 cm and indicating an increase of approximately 7 cm compared to what was obtained in 2001 (Fig. 4). These results led to carrying out in-depth investigations on the structure aimed at verifying its state of conservation/degradation. These activities have been valuable to achieve the level of knowledge required by the "Guidelines for risk classification and management, safety assessment and monitoring of existing bridges ". Therefore, a special inspection has been carried out aimed at detecting: structural defects and crack patterns of the prestressed reinforced concrete structures of the deck, mechanical characterization of the materials used for the construction, the state of conservation and the tension levels of the tendons and finally the characterization of the real behavior of the tie rod joints of the discontinuous spans.