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Fatigue Design of Thickness Transitions in Welded Steel Plate Girders

Fatigue is a critical aspect in the design and assessment of bridge girders. The local stress-raising effects caused by thickness transitions must therefore be accounted for through an appropriate stress concentration factor (SCF) when performing fatigue analyses.

Currently, prediction formulae for SCFs at thickness transitions are available in the literature, such as the paper of Taras and Unterweger (2013), which was later implemented in the concept version of the new standard EN 1993-1-9. However, these formulations show several shortcomings that motivate further research:

• Limited slope variation: Most available formulae assume a fixed transition slope of 1:4. The influence of other, more gradual slopes (e.g. 1:8) on the SCF has not yet been investigated.

• Influence of flange width and web stiffness: The resulting stresses vary along the flange width: near the plate edges, bending is mostly unrestrained, whereas closer to the web the bending becomes increasingly restrained, depending on the web stiffness. This effect and its influence should be investigated further.

• Single evaluation point: Existing SCF predictions are typically provided only at the toe of the transition, i.e. at the location of the butt weld. The variation of the stressraising effect with distance, especially when the weld is shifted away from the transition, has not yet been quantified.

• Neglected weld-induced stresses: The effect of flange eccentricity on vertical stresses in longitudinal (fillets) welds near the transition is not yet represented in current design approaches.