PSI - Issue 84

Antonella Cosentino et al. / Procedia Structural Integrity 84 (2026) 882–889

885

Fig. 3. Gerber saddle

The static safety evaluation The safety evaluation, carried out by the University of Pisa, had the main goal to verify the complete adequacy of the bridge to the traffic loads provided by the Technical Standards for Construction (NTC 2018). In case of inadequacy, its transitability by imposing suitable road use restrictions had to be verified, while waiting for the design and execution of maintenance interventions. The evaluations were preceded by a careful knowledge phase which was designed on several levels of depth, according to the Guidelines. Firstly, a preliminary "diffuse" knowledge campaign was conducted on the entire structure, consisting of a limited number of investigations on structural elements and construction details to perform preliminary analyses. The results provided by the preliminary verifications highlighted the need to increase and detail the knowledge. Based on these, in order to avoid redundant and unnecessary investigations and to deepen the aspects for which there was less knowledge, a further investigation campaign was designed and subsequently executed. The second investigation campaign included a greater number of destructive and non-destructive tests on materials and the execution of experimental dynamic analyses, using accelerometers to characterize the dynamic behavior of the bridge. The experimental dynamic analysis and the consequent calibration of the numerical modeling parameters - such as the stiffness of some nodes, the elastic modulus of the concrete, and the degree of constraint of the Gerber saddle - were particularly useful for calibrating the numerical model and performing more reliable analyses; due to the bridge's geometric configuration itself, the demand value and therefore the verification results were strongly influenced by the modeling assumptions. The summary table of the investigation campaigns performed is reported below.

Table 1. Summary of the investigation campaigns performed Investigation type

1th campaign

2th campaign

Visual inspections on structural details

16

6

Destructive tests - concrete Non-destructive tests - concrete Destructive tests - steel Non-destructive tests - steel

2 0 1 0

15 78

0

17

The number of samples and investigations depends also on the availability of the original project. Through the tests performed, excellent correspondence was found between the design details and the elements as-built. This circumstance allowed to avoid the need of simulated project and to proceed directly to a safety verification without redundant testing. The verification results showed that some structural elements did not have sufficient capacity to handle the traffic loads provided by the NTC 2018; therefore, the bridge was considered inadequate. The demand-to capacity ratios were higher than unity for several elements of the bridge (suspended beams, trestles, Gerber saddles, crossbeams), for both eccentric axial force and shear verification. Consequently, the transitability of the bridge was