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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Continuous bottom flange stiffeners were recommended before 1987. But, the actual bridge presented in Fig. 5 & 6 was designed with non continuous bottom stiffeners. The bridges were even experimentally “calculated” regarding fatigue, but bureaucrats decided not to consider details 1 and 2 because the class of the longitudinal stiffener (detail 1) did not directly appear in the tables of the ECCS recommendations. The modified stress was not calculated for detail 2 either. It was decided in 1993, after my visit of the bridge to inspect every year the two wrong details. M. Virlogeux also decided Setra would design a pilot box girder bridge project with the right details for such box girder bridges in Nevers [8,9] in order to promote box girders [10]. In straight line on the plan, the Nevers box girder was cheaper than a 2xI girder deck. However, the bureaucrats never introduced the Nevers bridge in the French guidance books.

Figure 5 : Cross section of the bridge

Fig 6-a : Detail 1, fatigue crack in a stiffener of the bottom flange of a box girder bridge

Fig 6-b : Detail 2, fatigue crack at the attachment of a transverse stiffening system

Fig 6-d : Probabilities of crack initiation

Fig 6-c : View of the mesh

Figure 6: Example of a box girder bridge The inspections were carried out regularly by the motorway company. During the same year 2014, the bottom flange stiffeners presented cracks at 16 different locations of the bridge which represents 50 % of all the details of type 1. The photo shows the more advanced crack that propagated into the bottom flange. Due to the geometry, the fatigue class along the cut is strongly reduced, from 125 MPa to about 40 or 50 MPa, according to the radius of the local cut, by considering the stress concentration factor with the same method also used to evaluate the cope holes in the present article. This class is coherent with the traffic on the motorway and the elapsed time between construction in 1989 and apparition of the cracks in 2014. Twenty different locations also presented cracks of type 2 during the inspection of October 2015.