PSI - Issue 44

Michele Frizzarin et al. / Procedia Structural Integrity 44 (2023) 745–749 Michele Frizzarin et al./ Structural Integrity Procedia 00 (2022) 000–000

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therefore to § 8.4.3 of the New Technical Standards for Construction, it is possible to make the considerations summarized in the following table.

Table 1. Considerations regarding the cases of adaptation of §8.4.3 NTC 2018, with reference to bridges. Current standard text (§8.4.3 NTC 2018) Applicability to bridges a) Building superelevation Not applicable b) Expansion through structurally connected works Can be classified as a local intervention (§ C.8.8.7 Application Circular 2019) c) Increase of the overall vertical loads in the foundation higher than 10% Applicable d) Transformation of the building through a

Applicable. In the case of modifications to the deck alone, it can be included as a local intervention (§ C.8.8.7 Application Circular 2019)

systematic set of works that lead to a structural system different from the previous one

e) Change in the class of use

Difficult to apply

Based on the table above, it can be seen that the most common case in which the intervention on the existing bridge must also include the adaptation of the substructures is case c). This intervention therefore involves the seismic adaptation of the bridge. This situation includes numerous types of interventions aimed at reinforcing and / or repairing the deck, for example by reinforcing the sections of the beams or the introduction of external post-tensioning or plating. Other typical interventions are those relating to the adaptation of safety barriers, which involve the remaking and / or widening of the curbs and the related reshaping of the road surface. For this type of intervention, it is essential to evaluate the increase in the global vertical loads in the foundation, and if these exceed 10%, provide for the adjustment of the entire structure. In this regard, the standard specifies that this increase must be evaluated according to the characteristic combination referred to in equation 2.5.2 of § 2.5.3 (rare SLE), including only the gravitational loads. However, it is not specified whether these "gravitational" loads include vehicle weights or traffic loads or not. This also in light of the fact that the same standard provides, where necessary, that a portion (20%) of the traffic loads is also used as a seismic mass (§ 5.1.3.12 NTC 2018). In the next chapter, the case study presented in the previous chapters is resumed, estimating the extent of the variation in foundation loads considering 100% or 20% of the variation in traffic loads, for the various regulations. 3.1. Comparison between regulations in terms of increasing vertical traffic loads The following two tables show the percentages of variation of the total foundation load, in the following hypotheses: • Weights g1 and g2 estimated at approximately 7.5 kN / m2 of deck; • Variation calculated with respect to the original weight of the bridge, with the formula: ∆ = ( − ) 1+ 2 + (1) Where W g1 + g2 are the permanent weights, Q oc are the traffic loads of the original standard at the time of construction of the bridge, Q nc are the traffic loads of the current standard (NTC2018) and α is equal to 1 or 0.2 depending on that consider 100% or 20% of the traffic loads. The results are expressed in the following table.