Fatigue – when weld detail is „starting to be“ the base material detail?

[Vitkacy1989]

Hi All,

The question is how to select proper reference stress when weld detail (fatigue category 112) is „starting to be“ the base material detail (fatigue category 140). In other words for what X-position one should use category 140?

Please see the picture:

 

[phamENG]

I'd say look at the crack initiation points. At each value of x, where would the crack initiate? If in the base material, use 140, but if in the filler or fusion plane use 112. Give yourself a 1 inch or 2*t margin, or whatever makes you comfortable.

In the states we classify them a little differently, but based on your sketch and the provisions of AISC Appendix 3, Design for Fatigue, I don't think you need to worry - just use 112. The threshold stress where fatigue becomes a consideration is much higher for the base material, but you're showing your highest stress near the weld. Therefore, it seems your weld and surrounding material would reach the fatigue threshold sooner and be the controlling part of the assembly.