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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1. Learning from experience Many steel structures have already reached or exceeded the limits of their original design life. They often span major rivers and carry major highways that are vital to the food supply of major cities. Among the problems encountered in metalbridges, fatigue is the majorcause of loss of serviceability in steel bridges [1] and the most common cause of failure. In order to make the right choices at the time of construction of these structures, as well as to decide on their appropriate rehabilitation, it is essential to make a correct estimation of the detail categories for all the features involved. The correct classification of the cope holes between the web and the flange is one of the sources of uncertainty identified that required investigation. Before 1987, the fatigue design of bridges features was considered in France as the art of choosing very progressive transitions of geometry to avoid stress concentrations. The finite element method was already used to evaluate stress concentration factor s. The conception of the steel parts of the new breech block for the “François 1er” movable flap bridge in Le Havre is an example of such a good design. This breech-block in Fig. 1 supporting the counterweights has to support a very severe range of stress variations, and in some locations even multiaxial fatigue stresses. Before its installation in 1986, the new breech-block with its rounded gussets was calculated using a finite element model [2]. 1.1. Examples of good fatigue designs

Figure 1:

The “François 1er” bridge in Le Havre and its new breech block installed in 1986

Figure 2: The Cannes overpass with its anti-fatigue rounded gussets