PSI - Issue 84

M. Cademartori et al. / Procedia Structural Integrity 84 (2026) 384–391

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square meter for longer structures. This raises the question of whether, at least for very small decks, direct replacement might sometimes be preferable to an investigation plan with a time and cost-consuming associated safety assessment.

Fig. 12. Knowledge completeness for calculation report, as built drawings, load test report of the bridge stock

Fig. 13. Investigation direct costs (€/m²) vs total bridge length classified by construction technology

4.3. Use of field loading tests in the assessment phase Load testing consists in observing how a bridge responds to a controlled load without altering its elastic behavior, and it is widely recognized in international guidelines. While commonly used for new bridges or deck replacements, its application during assessment of existing structures is still limited. The Italian Guidelines include load testing only as support for improving numerical models or for temporary load rating, and even then, the results cannot replace a full assessment. In contrast, standards such as AASHTO’s Manual of Bridge Evaluation and the British CS 463 give load testing a more central role, even allowing “proof load tests” as an alternative to analytical rating when calculations are inconclusive. These procedures often apply loads higher than service traffic to capture effects that are not directly measurable in the field. Recent research in the Eurocode context reinforces the value of such approaches. The authors argue that Italy should adopt a more refined methodology, since field tests can speed up assessments, reduce uncertainties, and compensate for missing documentation. However, differences between new and existing bridges— such as unknown safety margins or fragile details—should guide when and how load testing can be applied safely. 4.4. Investigation and verification issues for some elements: half-joints, deck slabs, abutments, bearings The assessment of existing bridges requires a deep understanding of several structural elements, many of which are difficult to access and inspect. Most common issues are listed below. • Half‑joints pose one of the greatest challenges because they are often hidden, prone to severe degradation, and lack structural redundancy, making both testing and verification complex. Their inspection is hindered by traffic constraints and by water infiltration near expansion joints, which can accelerate hidden damage. • Deck slabs also present difficulties, as testing must balance traffic management, asphalt restoration, and the physical constraints imposed by beam spacing and limited access below the deck. • Abutment walls add further uncertainty because internal reinforcements are usually inaccessible behind backfill, often requiring simulated design when drawings are missing. Realistic earth‑pressure modelling is also essential, since assuming static pressure may be overly conservative. • Finally, bearing devices frequently suffer from inaccessible locations and missing documentation, forcing engineers to rely on assumptions that heavily influence both static and seismic analyses due to the key role of support stiffness. Overall, the knowledge phase is therefore essential to reduce uncertainties and ensure assessments reflect the actual behavior of each structural element. A thorough and well‑designed investigation strategy ultimately enables safer, more reliable evaluations of existing bridges.