PSI - Issue 64

Dario De Domenico et al. / Procedia Structural Integrity 64 (2024) 784–790 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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1. Introduction Many bridges in the Italian infrastructure network are close to the end of their nominal service life, as they were built in the post-war economic growth of the 1950s (Pinto et al. 2010). In this context, monitoring and preserving such strategic structures have become an important focus for road management companies. This has contributed to the increasing interest towards the vibration-based structural health monitoring field (Farrar, and Worden 2007). A typical scheme, widely used for road overpasses built in Italy in the 1960-70s, relies on half-joints, also referred to as Gerber joints or dapped-end beams (Desnerck et al. 2018). Similarly, to simply supported structures, Gerber scheme-based ones are statically determined and therefore not influenced by thermal variation or differential settlements. On the other hand, some relevant drawbacks of this configuration are related to brittle shear failure of the half joint due to the reduced section height (Moreno-Martínez et al. 2014) and the corrosion of the protruding nib due to long-term water leakage (Di Prisco et al. 2023). Finally, it is worth mentioning the difficulty in visual inspection and defect detection due to the peculiar geometry. In this regard, vibration-based tests are widely adopted for the health assessment of existing bridges due to the ability to detect possible hidden damages even when visual inspection is not possible. In this context, this paper aims to assess the structural health conditions under service loads for a set of road overpasses part of the A20 highway (Sicily, Italy) characterized by a Niagara-type Gerber static scheme. To this aim, an experimental-numerical framework is adopted combining in-situ dynamic tests with a finite element (FE) model representative of the investigated structures. Free vibration tests are adopted to identify modal parameters in a cost-effective manner due to the rapid execution time as well as the limited number of sensors required (Mazzeo et al. 2024). The estimation of dynamic characteristics from the free vibration recordings is therefore carried out by exploiting a recently developed Variational Mode Decomposition-based framework (Mazzeo et al. 2023). This technique is specifically developed to deal with free vibration tests and is complemented by a robust area-ratio based approach for the estimation of modal damping ratios particularly suitable for reducing the sensitivity to noise disturbances that are likely observed during in-situ field tests on real-scale bridges. The experimental modal frequencies and damping ratios as well as the peculiarities of the extracted modal shapes of this kind of structures are illustrated and compared to the previsions of a FE model, properly calibrated based on material properties inferred from in-situ material characterization tests. This procedure allows to assess the actual health conditions for

the monitored overpasses. 2. Investigated structures

The case study object of this contribution is a set of road overpasses part of the A20 highway in Sicily (Italy) built in the early 1970s. Each prestressed concrete (PC) deck is based on a Niagara-type Gerber structural scheme consisting of two symmetric lateral spans of length equal to 29.0 m, terminating with dapped ends that support a central suspended span of 31.0 m as shown in Fig. 1.

Fig. 1. Photograph of a typical road overpass with Niagara-type Gerber scheme of the A20 highway (Italy).

Depending on the specific road overpass, the deck width ranges between 6.5 m and 17.0 m due to the variable number of PC I-shaped girders (3 to 8) equally spaced at 2.0 m from each other. The girders have variable heights