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RE: Sx in Tables 3-2 of New Steel Construction Manual ???[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: <seaint(--nospam--at)seaint.org>
- Subject: RE: Sx in Tables 3-2 of New Steel Construction Manual ???
- From: "Carter, Charlie" <carter(--nospam--at)aisc.org>
- Date: Tue, 18 Apr 2006 16:05:21 -0500
Thanks for the suggestion, but I don’t understand. Maybe you can explain further.
Why would you need to use Sx in Table 3-2? Though you could use it in place of Zx if you wanted to arbitrarily throw away capacity, it isn’t needed for W-shape beam design, particularly if you are using that table, which gives you all of the strength and length parameters for braced beams and beams unbraced up to Lr. That table sorts the beams by strength assuming you have the very typical case of a braced compact beam, which would make it a hunt and peck chore to find Sx for a given section as they are not listed in shape order. You can find Sx much more quickly in the Part 1 tables (Table 1-1 for W-shapes).
You said that Sx sometimes proves to be more practical and economical for beam design, but this is not ever the case for W-shapes. That is, the 1.6FySx limitation that sometimes limits nominal flexural strength is never reached for W-shapes because the largest shape factor for a W-shape in strong axis bending is around 1.3 – well short of the 1.6 factor on that part of the design rule.
I think the other values in that table are actually useful to cover design for an unbraced length up to Lr, deflection checks, and shear checks.
But maybe I am missing a gem in your suggestion. Please enlighten me.
From: Pedro Muñoz
It is unfortunate that Tables 3-2 do not have the Sx values side by side with the Zx values.
Recognizing that the New Steel Construction Manual presents a Unified method from now on, it should still be one that the Designers could put hands on and find the most common design values tabulated easily and conveniently, for small buildings and quick beam designs, the Sx values still prove to be practical and sometimes more economical than the designs obtained with the Zx values. AISC should consider to include the values of Sx in the new editions. Other tabulated values in Tables 3-2 Designers may never even have to use them, but Sx is a good reference and bench mark value, It should be included in Tables 3-2 of the Steel .Construction Manual.
Pedro R. Muñoz, Ph.D., P.E.
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