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RE: Channels - Weak-axis bending

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>Loosely, 0.9FyZ in LRFD translates to 0.66FyS in ASD. 
>a true translation from LRFD ... would
>be 0.9FyZ/1.5 = 0.6FyZ, assuming the effective load factor is 1.5.
This is interesting. The implication for this one case is that LRFD 
provisions can be taken as the corresponding ASD values, scaled upward by 
the load factor. Turns out the same thing happens for steel columns. The 
LRFD tables shown in the AISC Publication 'Essentials of LRFD' are almost 
exactly the ASD values scaled upward by a factor of 1/0.70 = 1.43. Close 
as dammit to the 1.4 factor for dead loading. I'd be very curious how 
closely the 1.2D+1.6L combination corresponds to 1.4(D+L) for ordinary 
ratios of live to dead load. 

The bending limit load provisions look like the usual plastic bending 
load of bygone days, so that's actual elastic-plastic limit analysis. The 
LRFD pure tension requirements are 0.9/0.6 = 1.5 times the ASD 
requirements--not too far from the 1.4 multiplier and equal to the 
effective load factor for weak axis bending in channels as Charlie Carter 
pointed out. Now I'm wondering how many other LRFD provisions are 
more-or-less ASD values factored upward. Could be that LRFD isn't so 
obscure as the revised terminology seems to imply.

Could also be that the 75%UTS effective stress for design against 
fracture is pretty optimistic for cases of brittle fracture. I understand 
that happens from time to time...


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)
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