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RE: Sx -Zx Strength-Deflection Tables 3-2 AISC Manual

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Thanks, I understand a little better now.

 

The comfort of Sx is incorporated in how the Basic Design Values cards are put together – all the flexural strength equations on those cards use Sx and the shape factor in a manner that is identical to the way 0.66FySx was obtained as the allowable in ASD (0.66 = 0.6 times the lower bound shape factor for W-shapes of 1.1). They are a free download at:

 

    www.aisc.org/2005spec

 

The Manual Committee will consider your suggestion. In the meantime, and since the shape factor for W-shapes ranges only from 1.1 to 1.3, you could probably get a very close and quick estimate of S from Table 3-2 by dividing Z by 1.2. And you can do the same thing to get 0.9FySx from phiMpx, which is simply 0.9FyZx for all but a handful of beams.

 

Charlie

 


From: Pedro Muñoz [mailto:prmz(--nospam--at)worldnet.att.net]
Sent: Wednesday, April 19, 2006 7:50 AM
To: seaint(--nospam--at)seaint.org
Subject: Sx -Zx Strength-Deflection Tables 3-2 AISC Manual

 

In many situations selection of W shapes are controlled by deflection or serviceability in which case a particular section may be way over the required Zx or at the service level the required Sx. A look of the required Sx values at the service level is still a good reference bench mark of strength design for service loads. Not intending to go back to the ASD design method but perhaps as a way to have the designers feel more comfortable making the transition from the old green ASD Manual to the new black Manual and not having to flip so many pages back to look for a value that used to be there in the Tables, may be a way to have the designers finally feel at home with one single Manual and perhaps start using the black Manual more often and immerse themselves into it. Similar to what happened with the Ix values in the Green Manual, one had to write the Ix values in a separate column just for convenience of having them right there.. Similarly to what is being done with presenting the values of ASD in green and the LRFD values in blue, it wouldn’t be a bad idea to have the Sx values right there in those Tables 3-2 next to the Zx values. Just a suggestion.

 

Pedro R. Munoz, Ph.D., P.E.

Newburyport, MA

E-mail: PRMeng(--nospam--at)att.net