Flange thickness transitions are an essential and frequent design detail for long-span girders in order to effectively adapt their cross-sections to variable bending moment curves. In the case of bridge girders, flange thickness transitions are also often combined with an assembly joint with an additional web cope hole in the area of the flange butt welds.

In the area of a flange thickness transition and cope hole, additional local stress and strain states arise due to the change in the stiffness ratios within the girder cross-section in the area of the construction detail, which are not correctly captured by the classical beam theory. In addition, the local stress and strain states influences the performance of the notch detail under fatigue loading and can significantly influence the fatigue life of a structure.

Although the flange thickness transition in combination with an assembly joint with cope hole is an efficient as well as popular and frequently executed design detail in engineering practice, its fatigue strength is neither covered in Eurocode 3 nor is its fatigue behaviour describes well in the literature.

The research project addresses the problem of plate and flange thickness transitions as existing in steel and composite bridge construction with special consideration of thick plates. On the basis of experimental studies, user-oriented models for the fatigue design are developed. In order to reflect the correct load-bearing and fatigue behaviour, large-scale fatigue tests are planned in addition to small scale tests at notch details, as well as combined analytical-numerical simulations using the notch strain and crack propagation concept (Two Stage Model). The project intendeds to ensure the future efficient execution of this design detail.