(V) Where Bridges may fail "by Fatigue" or in Long Terms Usage : a Prevention oriented Approach

Nowadays bridges are more and more subjected to dynamic loads due to the heavy traffic flows that are crossing those steel, beton or mixed structures. In steel bridge design, fatigue was always a given concern especially for structural members and welding/joining details (f.e. ENV3-1993 Part 9 or AISC SCM-2005 13Ed.). Anyway architectural & esthetic questions pull on the use of some specific and unconventional components that may require some given deep detailed checks under their potential "dynamic loading assumptions". The former "quasi-static assumptions" well justified by the importance of the dead loads vs the variable ones let place more and more nowadays to the endurance question of some structural details. Fatigue being amplified by many miscellaneous factors such as the component manufacturing process(es), their surface roughness, their residual stresses, the shapes of the load cases, the temperature and thermal deformation cycles, the environmental and corrosive influences, some specific unconventional construction details require nowadays to be detailed checked for their long lifetimes requirements (f.e. 100 [Years] !). Some distinction between the "mechanical" approach (Usually quite well known load cases, Usage Lifetime < 20 [Years], "Easy" Maintenance) and the "structural" one (Variety of unknown load cases, load cases combination criteria approach, Usage Lifetime >>> 20 [Years], No, low or difficult Maintenance) seem to exist. These fatigue calculation checks may also put in evidence different question of further construction details and how they are previewed, made during the work execution, controlled, "qualitatively" receipted and potentially maintained over their usually long required lifetimes. The FDM will be presented and some reference European standards such as ENV3-1993, EN1990, EN1090, ... will be explained. A non exhaustive prevention based talk where a case study of suspension bridge will be presented.