EN 1993-1-9 low cycle fatigue verification

[Pawel27]

Dear All,

I have question to section 8 of EN 1993-1-9. There is condition for stress range not to exceed 1,5fy and 1,5fy/(3)^0,5 (direct and shear stress respectively). Some times ago I read that if this condition is fullfilled then low cycle fatigue will not occur. I don't rememeber where I read it. I cannot find anything in EN 1993-1-9 about it. If You know where it is described or You can tell something more about relation between this condition and low cycle fatigue, please help.

 

[Agent666]

My reading of those limits are that its the maximum allowable stress range under the load cases that follows them.

Usually in fatigue there is a lower bound number of cycles and/or stress range where fatigue is not required to be checked. However, flicking through EN1993-1-9 I cannot see anything obvious like this (I'm not particularly familiar with the way Eurocode does fatigue though).

My understanding of the fundamentals of low cycle fatigue, is that its to do with the number of cycles in the inelastic range, i.e. under seismic loading after a few cycles you might get a fracture in yielding regions due to low cycle fatigue. I'm sure someone more knowledgeable in fatigue can clarify further. Its kind of like bending a piece of wire back and forth and it breaks after a few cycles, vs normal fatigue where the bending remains in the elastic range, and hence you can bend many many more times before it might break.

 

[Tommy385]

Agent666: Usually in fatigue there is a lower bound number of cycles and/or stress range where fatigue is not required to be checked

For cranes (EN 1993-6) that number is 10000 cycles

9 Fatigue assessment
9.1 Requirement for fatigue assessment
(1) Fatigue assessments according to EN 1993-1-9 should be carried out for all critical locations.
(2) Fatigue assessment need not be carried out for crane supporting structures if the number of cycles at more
than 50% of full pay load does not exceed Co
NOTE: The numerical value for Co may be defined in the National Annex. The recommended value is 10^4