PSI - Issue 84

Alessandro Scala et al. / Procedia Structural Integrity 84 (2026) 489–496

491

2. Prioritization indexes As previously mentioned, the structure of the method is based on the defect sheets used for structural risk assessment, in which the inspector is responsible for recording the presence, severity, and spatial extent of defects observable directly on the structure. Each defect is assigned a priori a weight G , ranging from 1 to 5, according to the severity of the observed evidence. This weight is then multiplied by two additional coefficients, k 1 and k 2 , representing other characteristics of the defect, such as extent and intensity. In this way, the sheets allow a single value to be assigned, summarizing the level of defectiveness of each structural element. Unlike structural risk assessment, landslide risk evaluation does not directly consider evidence observed on the structure; instead, the landslide CoA is primarily determined based on the characteristics of the phenomenon itself. Vulnerability is closely linked to the type of structure, while interaction with the landslide is included only as a secondary parameter. It should also be emphasized that the proposed method is not intended to link observed inspection signs to hypothesized causes, as the assessment conducted in the first three levels remains preliminary and general in nature. However, by dividing the index into pre- and post-inspection components, it becomes possible to both schedule the order of inspections and promptly identify structures that require more detailed analyses, based on the level of distress inferred from the observed evidence. =∑ ∗ℎ (1) The formula above (1) illustrates the concept underlying the two coefficients, where represents the weight assigned to each category of information (for example, the age of the bridge, average daily traffic, or any of the observable signs during inspection), while ℎ indicates the score corresponding to the selected level for each category. The index refers to the type of coefficient, which can be either pre- or post-inspection. The weights of the two coefficients are calibrated to yield a maximum value of 1, with higher indices identifying structures that require the highest prioritization for intervention. The pre-inspection index ( PI pre ) cannot, in practice, account for structural distress, unless it is already documented in the information available online or provided by the managing authority. For this reason, the categories that define it are based solely on data such as cartographic information (phenomenon documentation, mapped hazard, landslide type, extent of interference), structural information (history of closures, age, known deterioration of defect levels, geometry, materials, span widths, and foundation type), or other contextual or network-related information (date of the last inspection, type of crossed event, average traffic, presence of monitoring systems, seismology, slope inclination). Each category is assigned a weight, which in some cases may be negative, thereby reducing the urgency of carrying out the inspection. It should be emphasized that these categories do not alter the actual landslide risk faced by the bridge, but merely affect the prioritization for intervention, as in the case of the date of the last inspection or the documented presence of deep foundations. The post-inspection index ( PI post ) does not override the results obtained in the previous phase. The same categories are complemented with signs observable during the inspection, both on the structure and in the surrounding context (presented in the following chapter), along with some categories already included in the guidelines (presence of mitigation structures, estimated velocity, estimated volume, activity status of the phenomenon, and reliability of the assessment). This approach allows the previously assigned levels (option highlighted with an asterisk in the formula) to be updated based on the observations made during Level 1. The new categories added after the inspection account for more than two-thirds of the total coefficient value, which, as previously mentioned, has a maximum of 1. This highlights the importance of the inspection within the evaluation process, a step required by regulations, as all structures in the Italian infrastructure network must undergo at least the first two levels of the Guidelines. The calculated index is complementary to the five levels of CoA included in the guidelines, allowing for an additional nuance in the assessment. This makes it possible to differentiate, within the same class, the urgency of further investigation for one structure compared to another. Before presenting the results obtained through the application of the method, it is necessary to specify which signs can be associated with interaction with a landslide, as they constitute the core of the index calculation.