PSI - Issue 84

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

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Fig. 10. Flexural performance-based assessment of a prestressed concrete beam

Fig. 11. Minimum DIA factor value for selected assessed bridge within the bridge stock, with critical element

4.2. Knowledge-related Critical Issues Although the 102 bridges, viaducts, and flyovers presented in paragraph 3.1, only approximately 50% have undergone a complete safety assessment process in accordance with LLGG, at the time of writing of this paper.The low percentage of fully assessed structures is mainly due to the many complex tasks required for a reliable evaluation, especially the need for a performance-based investigation plan. A phased investigation—starting from visual and nondestructive tests and gradually refining data—helps reduce uncertainties and improves model accuracy. As knowledge increases, engineers can justify lower confidence and partial factors, achieving evaluations that better reflect real structural behavior. However, missing do cumentation (as shown in Fig. 1 2) and inaccessible components often require simulated design to reconstruct original assumptions. This step is essential to understand structural logic and safety margins when direct investigation is not feasible. The simulated design must be developed using the materials presumed to have been employed during the original construction and applying the load models and verification criteria prescribed by the codes in force at that time. Figure 1 shows that most bridges belong to distinct regulatory periods, each linked to specific design codes— ranging from the 1939 Royal Decree for pre‑1962 structures to the 1962 Circular and the 1980 Ministerial Decree for later ones. These codes embody the design philosophy and construction culture of their time, shaping safety margins and structural logic. Combining regulatory context with historical construction practices helps engineers build more realistic structural models and interpret test data more accurately. Simulated design is therefore essential when documentation is missing or details are inaccessible, ensuring a coherent reconstruction of original design assumptions. Finally, comparing bridge geometry with traditional rules of good practice— such as through the γc factor f or masonry arches—provides an additional layer of verification that enhances the reliability of the assessment. To complete the discussion on knowledge-related critical issues, it is essential to include some economic considerations. Alongside the investigation plan for each structureanalysed, a detailed cost estimationof the investigation campaign was prepared, allowing an assessment of the investment per square meter during the investigation phase alone. The results are plotted in Fig. 13: shorter structures tend to have higher costs per square meter, with a sharp decrease as the length increases, resulting in significantly lower costs per