PSI - Issue 62

Gianluca Bottin et al. / Procedia Structural Integrity 62 (2024) 177–184 G. Bottin et al./ Structural Integrity Procedia 00 (2019) 000–000

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1. Introduction In recent years the need to evaluate the residual capacity of existing infrastructure, which are approaching or exceeding their designed service life, has become a strategic issue worldwide. The definition of the mechanical characteristics and the degradation level of existing bridges has been widely investigated and nowadays there are different effective procedures for their assessment. In Italy, these aspects have been included within the general multi hazard and multi-level framework for safety assessment of existing bridges recently proposed by the “Guidelines for classification and risk management, safety assessment, and structural health monitoring of existing bridges” (2020), in the following refer as Guidelines. These Guidelines represent a novel fundamental step in the regulatory framework of existing bridges (Cosenza and Losanno, 2021). However, the degradation assessment is not fully sufficient to consolidate approaches to assess the residual capacity of existing structures. For this reason, a number of research projects have been activated to investigate, with hybrid numerical-experimental approaches, the behaviour of structural elements extracted from bridges and viaducts scheduled for demolition (e.g. Savino et al. 2023, Pape and Melchers 2013, Tonelli et al. 2023, Jiang et al. 2023). Most of these research projects deal with prestressed RC girders due to their intrinsic vulnerability and their extensive presence across the national road infrastructure system. Studies on cast-in-situ RC structural elements extracted from existing aged road infrastructure are limited, even if experimental data on their performances are crucial for a proper calibration of numerical models able to predict the life-cycle structural performance of RC elements. This paper presents the first phases of an experimental and numerical research on an almost 80-years-old RC bridge in a rural area of Veneto region scheduled for demolition. As part of the road system renewal project, it was scheduled the demolition of an existing three span Fratta river bridge located in Valli Mocenighe, Piacenza d'Adige (PD) and the subsequent realization of a new single-span bridge in a mixed steel-concrete structure. This was the starting point of a research project carried out jointly by University IUAV of Venice and University of Bologna. 2. The “Fratta” bridge: case study description and on-site test The Fratta bridge is located along the provincial road S.P. 91 - km 43+610 in Piacenza d'Adige (PD). The bridge was built in 1948 as can be deduced from the few available general documents. Fig. 1 shows an aerial view of the bridge and a global plan of the bridge. As visible from Fig. 1, the bridge does not intersect the Fratta river perpendicularly but with an angle of approximately 10°. Consequently, the entire geometry of the deck is skewed. The Fratta bridge consists of three structurally independent cast-on-site RC decks with about 12 m-long spans. Each span is 8.10 m wide and consists of four 1 m-high girders supporting a 20 cm-thick concrete slab. Three equidistant reinforced concrete cross-beams connect the longitudinal girders, one at the centre and two at the end. The central cross-beam has the same height as the longitudinal girder while the end ones are raised of approximately 20 cm compared to the intrados of the longitudinal girder itself. The bridge deck leans on fixed lead sheets bearings. The piers in the riverbed are 5.00 m high and are composed of two structurally independent side-by-side RC frames. The structural joint between the frames (and therefore between the decks) is approximately 2 cm. This space was used to absorb the thermal deformations of the span. The abutments are 2.80 m high with rear and wing walls containing the approach embankment. The piers and the abutments are founded on piles even if there is no specific information available on their constructive typology and length.

Fig. 1. Fratta bridge (Italy): (a) global view obtained with the drone survey; (b) top /lower plan view of the deck.