PSI - Issue 62

7

Alessandro Lipari et al. / Procedia Structural Integrity 62 (2024) 24–31 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 3. Bridge II: (a) main span view; (b) pier cap beam with spalled concrete.

3.2. Results and discussion According to the Italian guidelines, Bridge I has a high level of deterioration; consequently, the structural vulnerability class, the structural-foundational CA and the overall CA are all H, not being affected by other parameters or risks. The structural hazard and exposure classes are respectively MH and ML. Therefore, the structure has to undertake an L4 assessment; also, if deemed appropriate, an additional inspection and monitoring should be carried out. On the other hand, Bridge II hazard, vulnerability and exposure classes are respectively H, MH and H. The resulting structural CA is H and therefore the overall CA is also H, not being affected by any other risks. Therefore, just like Bridge I, the structure has to undertake an L4 assessment. It is quite surprising that both structures returned the same CA, in spite of Bridge II being in far better conditions than Bridge I. In fact, Bridge II’s CA is signi ficantly affected by its traffic volume (Table 1), which leads to both hazard and exposure classes H. However, it is quite clear that Bridge I is more in need of further actions than Bridge II. Therefore, a simple and straightforward prioritisation strategy within the structural CA H could be between bridges with level of deterioration H, whose safety may be at stake due to presence of severe defects in critical elements, and bridges with lower levels of deterioration, for which there is still time to monitor the evolution of the damage. Further, the case studies presented show that the outcome is strongly affected by the availability of suitable information, e.g., traffic-related data, and any conservative assumptions made in absence of data will likely lead to risk over-estimation. For example, if it could be demonstrated that for Bridge II the ADTT level is low (< 300 HGV/day/lane) and the ADT is at most of a medium level (< 25,000 veh/day), then both the hazard and exposure classes would decrease to MH and the structural CA to MH, with less onerous further actions for the bridge manager to take (i.e., an L3 assessment rather than an L4, see Fig. 1). When considering UK guidelines, the poor condition of Bridge I has also a significant impact on the need for structural assessment (Table 2). In addition, the presence of known hidden critical detail, such as the half-joints, further influences the need for assessment, as well as the change in condition since last design or assessment. The resultant action is therefore to carry out a structural assessment with a “Very High Priority” recommendation , based on a risk score of 4.0x10 -5 and a reliability score of 8.6x10 7 (Table 3). Bridge II is considered in fair condition, so whilst there are defects, these are not considered to significantly affect load bearing capacity. Unlike Bridge I, there are no significant hidden critical details and the change in condition is considered slight. The outcome for Bridge II is to simply review at the next Structural Review (typically in 12 years’ time ), based on a risk score of 500 and a reliability score of 7.46 (Table 3). In conclusion, both methodologies accord in assigning the top risk for the poor-conditioned Bridge I, whereas for Bridge II the outcomes are very much different. This suggests that parameters other than those related to the structure condition affect the outcome of the Italian method much more than the UK. As such, the Italian guidelines seem to be globally leading to more conservative results when evaluating the structural risk. A similar finding was noted in a comparative study of the Italian and UK guidelines on the hydraulic risk (Pregnolato et al., 2022).