PSI - Issue 78

Carlo Pettorruso et al. / Procedia Structural Integrity 78 (2026) 1190–1196

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X-Ray Radiography (XRR) offers direct visualization of internal components and can detect voids and accurately locate ducts (Täljsten et al. 2019). However, its practical application in the field is limited by logistical challenges and safety concerns related to radiation exposure. To evaluate the corrosion state of prestressing steel, electrochemical techniques such as Open-Circuit Potential (OCP) and Linear Polarization Resistance (LPR) are used. OCP provides an estimate of corrosion probability (ASTM), while LPR allows for an approximate evaluation of corrosion rate (Permeh et al 2022). Both techniques require electrical connection to the steel and are generally ineffective in detecting localized corrosion. Unlike the aforementioned techniques, prestress release methods aim to quantify the residual stress in concrete elements. The Saw-Cut Method (SCM), Kukay et al. (2010), and the Flat-Jack Test (FJT), Rossi et al. 2025, are semi-destructive but minimally invasive approaches, as they operate externally. In contrast, the Exposed Strand Method requires duct opening and direct force measurement on the tendons, resulting in a more invasive process. Lastly, X-Ray Diffraction (XRD), applied on an exposed strand, measures strain at the crystal lattice level to estimate stress in the steel. Despite its accuracy, it remains a complex and highly localized technique that typically requires numerical modeling for reliable interpretation (Morelli et al. 2021). 3. Framework for Selecting Investigation Methods A refined decision-making framework has been developed for evaluating and ranking Non-Destructive Testing (NDT) methods by Quaglini et al. (2023), building upon the approach proposed in NCHRP Research Report 848. The core of this methodology is a Weighted Sum Model (WSM) that calculates a comprehensive performance score for each NDT technique. This is achieved by evaluating each method across four key categories: accuracy, ease of use, traffic impact, and cost. Each category is assigned a specific weight, reflecting its importance in the decision context, and the final score is obtained by summing the weighted individual scores. Accuracy This category assesses how closely the NDT results match the actual condition of the structure (the "ground truth"), particularly in terms of damage detection and severity assessment. A discrete scoring system is used based on the deviation between measured and actual conditions. In cases where a method addresses both location and severity of defects, a combined accuracy score is assigned. Ease of Use Ease of use evaluates operational complexity through four subcategories: power demand, personnel demand, calibration, and data processing. Each subcategory is scored individually, and the final score is derived as their average. This category reflects the method’s practicality and suitability for real -world applications, with the possibility to apply custom weights depending on project-specific constraints (e.g., limited manpower or need for fast deployment). Traffic Impact This metric quantifies the level of disruption an NDT method causes to traffic flow, considering roadway occupancy and inspection duration. A traffic coefficient is applied based on contextual factors such as the average daily traffic (ADT), availability of detours, and whether the bridge serves strategic purposes (e.g., emergency access). These adjustments help tailor the impact score to the specific road network's sensitivity to disruptions. Cost Cost represents the total financial effort associated with the use of a method, including equipment, labor, and logistic expenses. To ensure comparability across methods, each method’s cost is normalized against the average cost of similar techniques addressing the same type of deterioration. This results in a standardized cost-effectiveness score.

Weighting and Decision Scenarios