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Re: Fatigue at Shear Connection Weld

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>"The stress range shall be computed as...the numerical sum of the maximum
>shearing stresses of opposite direction at the point of probable crack
>initiation."
That's a fairly turgid description. What they mean is to subtract the 
minimum shearing stress from the maximum shearing stress at the critical 
point. If the load reverses completely, say plus 8000 psi to minus 8000 
psi, the stress range is 16000 psi. If you go from unloaded to 8000 psi 
and back to unloaded the stress range is 8000 psi. 

I haven't taken a look at the LRFD fatigue provisions, but I suspect they 
aren't much different than the old ASD requirements. In Edition 8 you 
just go into Appendix B Fig B-1 to find your detail then go to Table B2 
to find the stress category and then to Table B3 to find the allowable 
stress. The stress category is a sort of rating for the susceptibility of 
a detail to fatigue failure. Category A is finished base metal and 
Category F is stitch welding or such, which is pretty awful. I don't use 
stitch welds--the economy of weld metal is more than offset by the cost 
of insuring that the starts and stops are clean.  

Christopher Wright P.E.    |"They couldn't hit an elephant from
chrisw(--nospam--at)skypoint.com        | this distance"   (last words of Gen.
___________________________| John Sedgwick, Spotsylvania 1864)
http://www.skypoint.com/~chrisw


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