Weld Fatigue

[dcarr82775]

I do not get into AASHTO much and I want to see if I am interpreting something correctly with respect to welding and fatigue. It isn't a bridge, but it is supposed to be designed per AASHTO.

I have a wide flange that is to be hung via a vertical knife plate located over and parallel to the web. I believe the weld of the knife plate to the wide flange falls under the condition shown in 5.4 of Table 6.6.1.2.3-1. Am I correct in assuming that the live load stress range in the weld metal needs to be less than or equal to 10ksi? I ask because it makes a fillet weld virtually impossible to use in this situation.

 

[a7x1984]

A graphic would be helpful.

"Structural engineering is the art of modelling materials we do not wholly understand into shapes we cannot..."...ah...screw it, we don't know what the heck we are doing.

 

[bridgebuster]

The threshold is 10 ksi meaning if your stress range is less than or equal to 10 ksi your detail will have infinite life. Otherwise, you can compute the mean life and the safe fatigue life.

 

[smjohns78]

I agree with bridgebuster. If you are looking for infinte life then yes, you are limited to 10ksi. In bridge design, you typically would not have a connection detail as you are describing or at least it would tend to not be heavily loaded so that this would not be an issue. Incidentally, this is pretty much the same requirement that you would fine in AISC Table A-3.1.