PSI - Issue 57

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

891

Fig. 32: Surface of the Scyotte bridge with weathering steel

Fig. 33: Surface of the similar other bridge with painted steel

The use of LP plates and level lowering at piers was economical in the 80s and 90s because it reduced the total amount of steel used in the bridge, but also because it eliminated most of the thickness transitions [7,8], which is excellent from a fatigue point of view [9]. The reduction in CO² emissions for the production of the steel was also reduced, however, the use of LP plates as well as the use of level-lowering after concreting only, was paradoxically abandoned when CO² emissions became an issue. The 2010 Guide about sustainable steel bridges [24] makes no mention of it. They were not used for the Scyotte River bridge. For example, the first bridge in the word with LP plates is the Joigny-sur-Meuse bridge [4] built in 1982 for a single span. LP plates have continuous varying thickness so that the butt welding of the flanges does not present thickness transition. Thickness transition is at the origin of fatigue weakness as shown in section 2.3 of the present paper. For bridges with multiples spans, the use of level lowering at the intermediate piers for the first time only after concreting also make the use of LP-Plates possible in Sedan in 1985 [6]. For the Lalong bridge, which carries the motorway between Bordeaux and Clermont-Ferrand, the Company Matiere was responsible for the design and was able to save around 10% of the steel required. This was obtained by level lowering at piers after concreting. The thickness transitions are also traps for water. This is not a problem when the steel is painted. However it becomes a issue with bridges made of weathering steel as shown in Figure 34. Again, it is not the risk of corrosion as a whole that is at issue, but the risk of fatigue cracking, for example at pit locations.