Fatigue in welded structures

[bljnv]

I am referring to BS 7608-1993 standard.
I would like to follow this standard for fabricated structures used in mobile equipments.
In section 3.1, it says the fatigue analysis procedure for welded structures is based on the assumption that only ranges of cyclic stress are considered for evaluating fatigue life i.e. mean stresses are neglected.
But for unwelded parts the mean stress correction is carried out while evaluating fatigue life.

I request the members to explain the why only range is considered for welded structures.
Thanks in advance.

 

[TomLee777]

Normally the tensile residual stresses are very high at welded connections. Even superimposed with compressive stresses, the resultant stress may still in tension. That's why mean stress is NORMALLY not considered. However, for some cases, mean stress may be considered. See [URL unfurl="true"]https://fatigue-life.com/welded-structures/[/url] for details.