PSI - Issue 84

Luca Ranedda et al. / Procedia Structural Integrity 84 (2026) 1191–1197

1195

Result quality

The survey is of a discontinuous type; the step used, between 0.75 m and 1.5 m, allowed results comparable to those of the area scan survey. Increasing the step reduces result quality, while decreasing the step reduces productivity. Sharp curvatures in the cable layout are difficult to reconstruct unless the step between scans is significantly reduced, which decreases productivity. Limited information is obtained on passive reinforcement. The personnel performing the survey must have basic engineering knowledge and be able to interpret the results obtained.

The area scan survey, being continuous, provides an excellent result, allowing detailed reconstruction of the cable layout, including possible sharp curvatures. A complete reconstruction of all passive reinforcement.

Personnel required

The personnel performing the survey are not required to interpret the data, so no engineering knowledge is needed.

4. Assessment of the Condition of the Prestressing Cables Following the identification of the prestressing cables, their condition was assessed through ultrasonic tomography and endoscopic inspections. Tomographic surveys were carried out on all cables on the right side of the buffer beam and on selected cables of the cantilevers. At locations where anomalies were detected through tomographic examination, endoscopic investigations were performed to verify the actual condition of the cable via direct visual inspection. The comparison aimed to evaluate the reliability of the instrumental surveys. 4.1. Ultrasonic Tomography The ultrasonic tomography method is a geophysical investigation technique based on the analysis of shear ultrasonic waves emitted by a series of bimodal piezoelectric transducers (transmitters–receivers). The emitted waves are partially reflected by discontinuities encountered along their path within the medium and are acquired on the surface by the same transducers. It should be noted that, in a manner opposite and complementary to the GPR technique, for ultrasonic waves the reflection coefficient R is equal to 1 (total reflection) in the case of air and 0.43 (partial reflection) in the case of metallic elements. This implies that ultrasonic testing allows: – Investigation beyond metallic elements; however, it may be difficult to detect small or limited metallic elements; – Detection of voids, even at depth and of small size; however, the presence of large voids, even if of limited thickness, may hinder deep analysis. The surveys were carried out using a Proceq Pundit PD8000 Pro tomograph (Figure 7), consisting of a grid of 24 (3 × 8) bimodal piezoelectric transducers (transmitters and receivers). Measurements are performed automatically, with one transducer emitting while all others receive the echo signal. The signal is analysed in the time domain using a SAFT (Synthetic Aperture Focusing Technique) algorithm and displayed in real time on the instrument as a tomogram (a diagram representing the propagation velocity of ultrasonic waves as a function of depth and the progressive movement of the probe). The scans were acquired at a frequency of 60 kHz with a time window of 600 μ s.

Figure 7 – Ultrasonic Tomograph Proceq Pundit PD8000 Pro