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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Fig. 3. M32 Flow chart summarizing all the investigation campaigns carried out as part of surveillance activities.

The results of the visual inspection showed a good state of conservation of the prestressing system with the execution of borehole visual inspections and a widespread crack pattern consistent with the deformations of the deck. This last aspect suggested to carry out an in-depth investigation aimed at evaluating the real structural behavior of the joints. This paper aims to describe the on-site tests and instrumental surveys related to the discontinuity joints of the decks. In particular the following aspects will be covered: • Axial stress evaluation of the Dywidag bars of the special joints considering only the dead load, using two techniques: the first with a dynamic method through the natural frequencies of vibration evaluation while the second with diffractometric measurements. • Measurement of vertical displacements and monitoring of the of the Dywidag bars axial stress with the dynamic and strain gauge methods under a static load test carried out at the joint of the span 7. • Measurement of vertical displacements and monitoring of the Dywidag bars axial stress in correspondence of an exceptional transport (150 ton).

Fig. 4. Diagram of the vertical deformation compared to the level of the deck.

4. Axial stress evaluation of the joint bars under dead load

The axial stress of the Dywidag bars was evaluated using two different techniques: the first using the vibrating wire method evaluating the vibration frequency with MM technique while the second involving the XRD.

4.1. Vibrating Wire Method

The technique permits the stress evaluation on a taut wire by characterizing its vibration frequency and their mass. Given a taut wire characterized by the following parameters: length (L), weight (p), cross section (A), flexural stiffness (EI) and by n natural frequencies of transverse vibration f n , the tensile stress ( σ ) to which the wire is subjected is given by:                  (1) Therefore, once knowing the physical and geometric characteristics of the wire and by evaluating its vibration