PSI - Issue 64

Marco Carlo Rampini et al. / Procedia Structural Integrity 64 (2024) 2141–2148 Author name / Structural Integrity Procedia 00 (2019) 000–000

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to remedy to damage and to arrest the degradation evolution. This kind of information is of fundamental importance to formulate the first hypotheses on the degradation causes and to plan the following steps. Then, a visual inspection with non-destructive techniques is generally carried out, aimed at detecting the presence of construction errors or damage consequences as presence of corrosion products, cracks, or cover detachment. During the detailed inspection, a sufficient amount of both non-destructive and destructive analyses is performed to arrive at a correct diagnosis of the causes of degradation and to assess the current condition of the structure. Several non-destructive techniques are available, providing a variety of useful information, such as concrete characteristics or corrosion conditions of reinforcement. Sampling, which is essential for arriving at a correct diagnosis and for estimating future evolution, must be limited to some representative areas, due to its invasiveness. Moreover, the types of analysis to be performed are strongly correlated with the construction typology of the structure under analysis. In this work, the results of the diagnostic campaign performed on the hangers removed by the 70-years-old arch bridge located in Italy between the cities of Canonica and Vaprio d’Adda, on the border between the province of Bergamo and Milano, are presented. The main aim is to check the reliability of a preliminary assessment of the bridge structural health by diagnostic techniques. This Nielsen type bridge was subjected to a significant intervention of maintenance at mid-2023; the hangers were removed, transported and stored at the laboratory of the Lecco Campus of Politecnico di Milano, and subsequently subjected to mini-invasive diagnosis simulating what could have been performed in situ before their removal.

Nomenclature Ø

radius of smooth steel bars

Ø ext

external radius of the reinforced concrete tie roads electrical resistivity of concrete measured in [Ω∙m]

ρ

2. Description of the case study: the bridge in Canonica and Vaprio d’Adda 2.1. Description of the bridge and of the recent maintenance intervention

The investigated bridge, originally called “Ponte di Aureolo”, is located between the cities of Canonica and Vaprio d’Adda, in province of Bergamo (Italy), overpassing the Adda river. The current bridge, inaugurated in 1957, is a Nielsen type arch bridge around 75 m long, composed of two parallel reinforced concrete arch, two lanes RC deck, and 36 inclined RC hangers (18 for each side), with a maximum length of around 10 m (see the side view in Figure 1a and drawings in Figure 2). As documented by Danciu et al. (2023) and Tveit (2019), Nielsen bridges, originally patented in Sweden in 1926, were diffused especially in the northern Europe after the II World War. They are realized with V-shaped cables/ties, resembling the diagonals of a truss, which significantly reduced deflection and forces in the vertical plane, as reported by García-Guerrero and Jorquera-Lucerga (2020). The original RC tie rods were composed by a series of smooth bars of different sizes: 7 centered Ø30 mm, 6 Ø16 mm, and 12 Ø8 mm bars. The tie rods were anchored in the upper arches by a hook connection, bending only the larger diameter central bars (Ø30 and Ø16 mm). These therefore represented the elements with the greatest significance from the point of view of the structural response of the individual hanger. Steel rebar was then covered with a layer of mortar up to an external diameter, Ø ext , originally equal to 102.7 mm. Details of both the section and anchorage of the tie rods are shown in Figure 3. a b c

Fig. 1. Side view of the bridge during the intervention of tie rods removal (a), temporary storage (b) and transportation (c) of the RC hangers.