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RE: Channels - Weak-axis bending
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- Subject: RE: Channels - Weak-axis bending
- From: Christopher Wright <chrisw(--nospam--at)skypoint.com>
- Date: Fri, 24 Sep 99 17:23:46 -0500
>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) http://www.skypoint.com/~chrisw
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