PSI - Issue 62

364 Simone Celati et al. / Procedia Structural Integrity 62 (2024) 361–368 , , and can be evaluated following Darmawan and Stewart (2007). Stress corrosion cracking is not considered due to its low probability of occurrence compared to pitting corrosion (Li et al. (2008)). ( , , )= 0.54 (− ( 0.54 − )) (− (− ( 0.54 − ))) ; > (5) Given the maximum pit depth, the residual area can be estimated using the following equation (Val and Melchers (1997)): { 02 4 − 1 − 2 ( ) ≤ √ 2 2 0 1 − 2 √ 2 2 0 < ( ) ≤ 0 0 ( ) > 0 (6) 0 is the wire's diameter [mm] and the geometric parameters 1 and 2 are outlined in Val and Melchers (1997). The corrosion current density is herein evaluated as follows (DuraCrete, 2000): = , , ∙ 0.0116 (7) and depends by the rate of corrosion when active ( , , ) [mm/year] and the time of wetness ( ) variables. 3. Probabilistic model A probabilistic approach is necessary to estimate the time-dependent reliability. Both capacity and demand are defined by the mechanical models and their input random variables. The degradation process embeds the time variability of the capacity and permits the evaluation of the residual lifetime of a structure. To understand the potentialities in terms of structural lifetime extension of the proposed corrosion model, it is used for assessing the reliability of a prestressed girder chosen as an illustrative example. This specific girder is 45 metres in length, is simply supported, and is prestressed using six post-tensioned cables each consisting of 42 wires. Its height measures 2.40 metres, and it is accompanied by a slab that is 20 centimetres in height and 2.8 metres in width, which acts in conjunction with the main beam. The selection of this girder type is deliberate, as similar beams are commonly found within the Italian highway bridge heritage. Besides the degradation model, the full probabilistic model accounts for materials’ mechanical characteristics, capacity and demand model uncertainties, and geometric c haracteristics, and failure is herein defined as the reaching of the yielding resistant bending at the midspan section. Fig. 1a depicts the mid-span section of the deck girder, whereas Fig. 1b shows the arrangement of the cables within the mid-span. The LSF, ( , ) , in which is the vector of the input variables, is defined as the difference between bending capacity and demand. 4 Simone Celati et alii/ Structural Integrity Procedia 00 (2019) 000 – 000

a)

b)

Fig. 1. a) Cross-section of the girder at the mid-span ; b) Cables’ arrangement at the midspan section