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Fatigue. Most trivial questions... |
Pingen
Member
Posts: 2
Joined: 17.10.07 |
| Posted on 17-10-2007 09:51 |
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Hi,
So, I have EN 1993-1-9 in front of me, and I don't get it at all.
I have several questions but I'll begin with just one. What is delta-sigma-E,2? Is it a modified value of the stress range that occurs in the structure? In that case, why is it specified that it corresponds to Nc = 2e6 cycles (section 6.1.2)?
Regards,
Pingen |
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| Author |
RE: Fatigue. Most trivial questions... |
Pingen
Member
Posts: 2
Joined: 17.10.07 |
| Posted on 17-10-2007 12:31 |
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Is the bottom-line that the structure must be able to handle at least 2e6 cycles, no matter what? Tricky to get around that idea, but what other conclusion could tie it all together? |
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| Author |
RE: Fatigue. Most trivial questions... |
Ditmar
Member
Posts: 4
Joined: 28.09.07 |
| Posted on 29-10-2007 11:59 |
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No, the stress referred to by the detail category (DC160 -> delta-sigma C=160MPa) is the maximum stress range for 2E6 cycles or vice versa. For other stress ranges and cycles (stress range-cycle-spectra) the Palmgren-Miner rule is used.
On the other hand for e.g. crane runway beams and bridges the rules are simplified to a simple stress-check by applying the lambda-method. The lambda coefficient being dependent on the spectrum.
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| Author |
RE: Fatigue. Most trivial questions... |
Ditmar
Member
Posts: 4
Joined: 28.09.07 |
| Posted on 29-10-2007 12:08 |
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delta sigma E2 is a nominal stress. E.g. take a crane on crane way girder (simply supported beam). delta sigma is the stress due to the presence of the fatigue load of the crane (gamma Ff*Qk). The lambda coefficient is function of the class of total number of cycles (Ui) and the class of load spectrum (Qi). Delta sigma E2=delta sigma*lambda. |
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