PSI - Issue 84

Chiara Galatà et al. / Procedia Structural Integrity 84 (2026) 1–8

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1. Introduction Bridges are a cornerstone of modern mobility. Among them, post–tensioned prestressed concrete (PTPC) bridges stand out for high performance in strength, durability and safety. Like all infrastructure, however, PTPC bridges are prone to deterioration and degradation that may compromise functionality and safety – most notably concrete cracking, corrosion of prestressing steel and loss of tendon prestress – phenomena that require in–depth diagnostics and continuous monitoring. PT systems became widespread from the 1950s onward for medium to long–span viaducts because they enable slender box–girders and efficient multi–girder decks, with high–strength steel strands anchored at deviators and end blocks and, in bonded systems, grouted within ducts. In these bridges, typical vulnerability drivers are hidden or partially hidden: grout voids and bleeding, moisture ingress along ducts and anchorages, chloride or sulphate contamination of grout, hydrogen embrittlement and stress–corrosion cracking of high–strength wires, as well as time–dependent effects that reduce effective prestress. Because many defects are not directly visible, reliable condition appraisal hinges on a toolbox that combines targeted visual inspections with non–destructive tests (e.g., ground–penetrating radar and ultrasonic/impact–echo to detect duct voids, tomography and endoscopy of anchorages), selective sampling of grout and tendons for laboratory testing, and complementary global methods (dynamic testing, vibration–based indicators, model updating) to infer stiffness loss. For safety–critical elements, continuous or event– based monitoring is increasingly adopted – e.g., acoustic emission for wire–break detection, load/response monitoring – to track deterioration kinetics and to support decision thresholds for restrictions, strengthening, or detailed assessment. This study focuses on these issues and on how different regulatory frameworks address inspection, risk assessment and maintenance of existing PTPC bridges. We compare the Italian MIT 2020 Guidelines (MIT, 2020) and related large-scale applications/critical analyses (Di Sano et al., 2023; Natali et al., 2023; Santarsiero et al., 2021) with established international references from the United States (NBIS/BIRM and Caltrans) (Michael B. Johnson et al., 2017; Thomas W. Ryan et al., 2023), France (ITSEOA/CEREMA fascicles) (Cerema, 2023) and the Netherlands (Rijkswaterstaat/CUR/TNO). While several documents exist, few comparative studies examine their practical implications for PTPC grid deck bridges and contrast risk–based, catalogue–based and probabilistic approaches on real assets. We contribute (i) a structured comparison of provisions on inspection levels, defect classification, decision criteria and monitoring, and (ii) evidence from 20 PTPC grid deck bridges on the Catania–Palermo motorway, discussing how the different frameworks would interpret observed defects and priority classes. The paper is organised as follows: section 2 outlines the regulatory frameworks; section 3 presents the case studies analysed by the Italian MIT Guidelines, section 4 reports the interpretation of the case studies with the other regulations presented the case studies; section 5 concludes with recommendations and suggestions for better use of standards for harmonisation and future work. 2. Regulatory frameworks for existing PTPC bridges 2.1. Italy – MIT 2020 Guidelines The Italian Guidelines for the Classification and Management of Risk, Safety Assessment, and Monitoring of Existing Bridges adopt a risk–based six–level workflow (Levels 0–5) to move from inventory and visual inspections to detailed assessments and network studies, enabling prioritisation via Attention Classes (AC) derived from hazard, vulnerability, and exposure condition. A large–scale implementation confirming the practicality of this multi–level approach (Levels 0–2 roll–out, with Level 1 defect sheets feeding AC at Level 2) is documented by (Iiritano et al., 2023). For PTPC bridges, the Guidelines introduce at level 4 special inspections (e.g., pacometry, GPR, ultrasonic/impact–echo, electrochemical methods; endoscopy, tendon stress checks) to detect tendon/anchor–zone anomalies not visible in standard surveys. In practice, within vulnerability parameters, the defectiveness level typically governs AC and thus the priority of further checks/mitigations. 2.2. United States – Federal framework (NBIS/BIRM + AASHTO MBE) and Caltrans The U.S. programme is governed by National Bridge Inspection Standards (NBIS) and implemented via FHWA’s Bridge Inspector’s Reference Manual (BIRM, rev. 2023) (Thomas W. Ryan et al., 2023) and the AASHTO Manual