PSI - Issue 57

Jacques BERTHELLEMY et al. / Procedia Structural Integrity 57 (2024) 872–903 J. Berthellemy / Structural Integrity Procedia 00 (2023) 000 – 000

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Figure 34: Trap for the water on the Scyotte River Grattery bridge at a thickness transition butt weld. Note that some bird droppings are also present.

5.5 The fatigue crack initiation danger due to pits that can occur because of bird droppings “Birds represent a menace to outdoor monuments” according to Vasiliu et al. “It is well known that birds are a nuisance for bridges” according to professor M. Virlogeux. “ Droppings actually contain 4% soluble salts, including halite, sylvite, potassium calcium sulphate, aphthitalite, apatite group minerals, wed- dellite, and gypsum”. “Few studies in the field of conservation have investigated the effect of bird droppings on materials” according to a r esearch on effects of bird excrement on metal materia ls by K. Balogh Z. Slížková K. Kreislová of the Czech Academy of Sciences. In the USA, weathering steel is mainly used for decks with 4 to 6 I-girders insuring a high redundancy. The USA experience shows that some W-steel bridge owners tried to protect their asset with fences. Birds can actually take advantage of this protection. On top of that, some bridge owners have had to face angry bird conservationists in court, arguing that the birds were being trapped!

Fig 35-b: Birds seem to perch where the bridge is most vulnerable (Photo M. Virlogeux, 2022).

Fig 35-a: Fences supposed to stop birds actually may trap them inside the bridge

In order to avoid fatigue cracks, the main challenge in monitoring bridges made in waethering steel is to ensure that corrosion pitting does not occur. If the protective oxide layer has some holes in the surface protection, corrosion pits may appear under the bird droppings. Powerful adapted blasting to pre-stress the surface is required to remove recently formed pits and, if necessary, in local association with TIG dressing for the deepest pits if needed. The use