PSI - Issue 38

Jacques Berthellemy et al. / Procedia Structural Integrity 38 (2022) 428–446 Jacques Berthellemy / Structural Integrity Procedia 00 (2021) 000 – 000

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The use of box girders and LP plates were promoted by Cerema (called Setra at that time) to reduce the height of the thickness transitions as well for single spans [4] as for multiple spans bridges in association with a lowering of the intermediate piers after concreting of the deck. The oldest fully welded bridge in the world already in service in 2021 is the French Neuilly bridge that has carried heavy traffic during 80 years without fatigue cracks. No cope holes were used. Bridge Cope holes were only found exceptionally on bridges in the 1960s and 1970s, and one example was found at the ends of additional cover plates to facilitate assembly (Fig. 3-a: A31 motorway), which aggravated the problem. As their poor fatigue resistance was known at that time [5], they were avoided from the end of the 1970s. The very innovative motorway bridge of Sedan was in 1985 the first welded bridge in France with a constant beam height where the difference of flange thickness were accompanied by corresponding opposite variation of the web height. According to the recommendations of Ch. Brignon, the web-flange fillet welds were therefore built stronger in the transition zone for the 48-70 mm thickness transition [6]. As shown in Fig. 3-b, the cope hole was also avoided for this flange butt-weld realized on site between two prefabricated segments assembled in factory.

Fig 3-a : Very poor arrangements on a bridge built for the A31 in 1971, at cover plate end with a 245 mm long cope hole

Fig 3-b : Sedan’s motorway bridge features realized by Baudin-Chateauneuf in 1986 Figure 3 : Before 1987 cope hopes (3-a) were used exceptionally and “ seagull wing ” were preferred (3-b)

Modern FEM analysis tools can put in evidence the difference between the two most usual geometries, weather the transition of thickness is obtained by the inside or the outside of the beam [7]. In the Fig. 4, the signed von Mises are at the same scale for both geometries and their ratio in the web near the weld is in a usual case of about 10%.

Figure 4: Recalculations in 2011 of inside and outside features for comparison

1.2. Examples of poor fatigue design inside a box girder bridge However, the fatigue design after 1987 was only based on calculations with the tables of detail categories proposed in the future Eurocodes. Every detail was optimistically supposed to be already covered by one of the existing tables. As a consequence, some details that were not classified in those tables were ignored even if they were considered as wrong before, and the cope hole problem is not actually the unique example of misinterpretation of the fatigue calculation rules that were introduced in France after 1987.