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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2.3. Rebars survey and material characterization. Due to the lack of original design documentation, it was necessary to combine different diagnostic techniques, such as metal-detector and GPR (Ground Penetrating Radar), Cheilakou et al. (2013), to estimate the reinforcement layout of the existing structure (girders and slab). Fig. 4 depicts the reinforcement layout obtained from the diagnostic activities. It is worth nothing that an accurate survey of the reinforcement layout is crucial for carrying out reliable predictive assessment of the load bearing capacity of the girders. The reliability of the detected layout was therefore verified with the information obtained from the demolished spans (Fig. 4b).

Fig. 4. Reinforcing survey of the lateral bridge beam: (a) geometrical details and (b) photo of demolished span.

In order to characterize the properties of materials and provide the most accurate input parameters for the numerical models (carried out to validate the design of the experimental setup - see section 3.3) the following tests (divided basing on the material investigated) were performed: - 8 cylindric concrete cores sampled from cross-beams and slab: compression tests with measurements of elastic modulus (4 samples); density measurements, and carbonation tests; - 7 reinforcement steel sampled during the demolition phases: tensile stress tests of bars. The concrete cores were extracted by drilling through the structural elements. Reinforcement bars with 14mm e 28mm of diameter were extracted from the spans scheduled for complete demolition. In Table 1 a short synthesis of the experimental results can be found.

3. The “Fratta” bridge: design of laboratory test 3.1. Design of the controlled bridge demolition

Controlled demolition of one span of the existing Fratta bridge was designed in order to use the girders for subsequent laboratory research. More in detail, four girders were extracted from the end span of the bridge on the Piacenza d’Adige side according to the demolition scheme represented in Fig. 5. The red cutting lines highlighted in Fig. 5a show that girders were sampled limiting the demolition of the slab (and therefore of the end and middle transversal girders) and preserving the T-cross section with a representative flange width. Dimension and weight of the girders resulted compatible with the lifting and road transport limits of vehicles.

Fig. 5. Demolition scheme with the indication of the cutting lines for the end span. (a) plan view and cross section; (b) photo of lifting phase after controlled demolition of the deck.