Keywords: prestressed concrete bridges, investigation plans, non-destructive testing, residual stress measurement, x?ray diffraction, release tests on concrete, levels of knowledge.

Prestressed concrete bridges on the Italian railway network represent a small portion of the overall asset inventory but a significant share of the total span count, with a predominance of pre?tensioned simply supported decks. Their potential vulnerability—particularly in post?tensioned systems—combined with evolving regulations and testing technologies motivates the adoption of standardized, repeatable investigation procedures. This paper presents a five?step assessment workflow comprising: historical review, preliminary homogeneity analysis (geometry, prestressing system, detailing, materials), targeted test campaign, homogeneity verification, and, when required, an integrative testing phase. The methodology addresses constructive detailing, in?situ material characterization (concrete and rebar), and the prestressing system. Applied techniques include ground?penetrating radar for tendon profiling, ultrasonic tomography for post?tensioned ducts (validated via endoscopy and direct inspections), direct residual stress measurements on tendons (release tests and X-ray diffraction), and indirect concrete?release testing. Sample sizes are statistically calibrated—using Student’s t?distribution for steel strength and hypergeometric sampling for defective?tendon detection—enabling appropriate knowledge levels through a balanced combination of direct and indirect tests. The proposed approach reduces invasiveness, time and cost, supports structural assessments, when needed, and re?classification (axle loads and/or speed), and is formalized within the Rete Ferroviaria Italiana Guidelines issued for experimental application.

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