Evaluation regarding fatigue for various type of hangers used for tied arch bridges

Abstract

The roads represent an important heritage owned by the French Ministry of Transports. Even more than corrosion, the fatigue is the principal aging process that affects the durability of steel bridges. Several examples illustrate in the article the importance of affecting a right consideration to the fatigue design of bridges.Details that may appear as accessory to most of the usual bridge designers may be in fact of a crucial importance. It is in particular the case of the welded joints. The fillet joints are much more sensible to the fatigue stresses and should be avoided when there is a doubt, because their evaluation is very complicated. If the designer of a bridge uses such attachment, he has to verify the relevance regarding fatigue before calling for tender because the time for such studies is generally not available during the execution studies.Calculation FEM techniques are used to evaluate the stress concentration factor that has to be taken into account for the fatigue design. For bridges, many fatigue details are classified in the Eurocode 3 ( part 9 ) from tests. But some details that cannot be found in the Eurocode, and can however be studied and evaluated by computation. Several examples of tied arch bridges are presented. The article presents also an example where the fatigue class of the detail regarding longitudinal stresses is evaluated thanks to a FE-modelization according to the 2008 IIW Fatigue Recommendations at the location of the attachment of a hanger.Crack in a similar fillet weld of the attachment of the stiffener of a box girder bridge is presented to illustrate that fatigue may really cause severe trouble.