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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1. Learning from experience A large number of steel structures have already reached or even exceeded the limit of their initial design fatigue life. They often bridge large rivers and carry important motorways that are essentials for the provision of foodstuffs for the main towns. Among the problems met in metal bridges, fatigue is the major reason for losing the serviceability of steel bridges [1], as well as the most common cause of failure. To make the right choices at the construction time of these structures, as well as to decide their pertinent rehabilitation, it is essential to make the correct estimation of the detail categories for all the involved features. The right classification of the cope holes between web and flange is one the causes of uncertainty that has been detected and needed an investigation. 1.1. Examples of good fatigue designs 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 s tress concentration factors. 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].

Figure 1: The “François 1er” bridge in Le Havre and its new breech block installed in 1986 Similar rounded gussets were also used for instance for the smaller overpass bridge of Cannes with a very strong plane curvature due to a radius of only 46m presented in Fig. 2. [3].

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