AISC Design Guide 25 1

[OUe]

I am analyzing an ordinary moment frame of steel using the AISC Design Guide 25. I had built extensive spreadsheets to calculate stress ratios from the AISC 9th edition, appendix F, and am now getting familiar with the new design guide. I am currently struggling to find the understanding of how this design guide would be codified in language of the IBC 2009. Should I still be using AISC 9th edition since the design guide 25 came out after the adoption of IBC 2009?

The main difference that I see in the AISC design guide 25 is the use of P-delta effects and the design guide goes into great detail using 2nd order effects and gives alternatives for using the amplified 1st order effects.

Any comment is welcome. Thanks.

 

[ajh1]

The Guide is just that, a guide or a suggested practice. It is not directly intended to get to the level of a mandatory design specification, although now that AISC has taken any tapered member references out of the main AISC spec there are no published design practices or requirements for a tapered member other than those presented in the guide. You can certainly use it with any code edition, in my opinion, based on a state-of-the-art approach, but someone could use other approaches not documented in the guide and be just as "correct" as using the guide. In theory, if questioned about an approach the guide would at least show you were using a published guideline as opposed to dreaming something up out of the blue.

 

[OUe]

ajh1,

While I agree with you on the design guide issue, I think previous code editions gave a codified approach (the 9th edition). With that logic, I suppose I will make sure that the 9th edition works, and I will probably take the approach of employing P-delta effects in a separate calculation. The 25th design guide is very very tough to make a spreadsheet. I've got a M+P stress ratio done on 4 cuts thru a tapered section, and I'm at a very very condensed 4 page spreadsheet already.

Thanks for the comment!

 

[wannabeSE]

The 2009 IBC does not reference the 9th edition (Green Book with the 1989 Specification for Structural Steel Buildings -ASD ). It references AISC 360-05, "Specification for Structural Steel Buildings" which is included in the 13th edition of the Steel Construction Manual (Black Book). There is also a 14th edition that includes the AISC 360-10 specification. The newest specification is a free download for everyone on AISC's website. The 2012 IBC references this newer steel specification. I have not looked at Design Guide 25, but I would assume that it is coordinated with the 2005 or 2010 specification rather than the 1989 (9th edition).

 

[SteveGregory]

Page 1 of Design Guide 25...
"The methods contained herein are primarily interpretations
of, and extensions to, the provisions of the 2005 AISC
Specification for Structural Steel Buildings (AISC, 2005),
hereafter referred to as the AISC Specification. The recommendations
of this document apply equally to the 2010 AISC
Specification for Structural Steel Buildings, although some
section and equation numbers have changed in the 2010
AISC Specification. These recommendations are not intended
to apply to structures designed using earlier editions of
the AISC Specification."

 

[JoshPlumSE]

Thank you SteveGregory. I was about to say the same thing. A couple of additional thoughts about DG-25:

1) Analysis requirements to comply with the design guide recommendations are significantly more stringent than those in older AISC codes. This includes not only P-Delta (and P-Little Delta) anlysis, but also more explicit considerations of out-of-plumbness or out-of-straightness and Stiffness reduction due to residual stress.

2) The design guide features failure modes that are never addressed in the older AISC codes. Specifically Torsional Buckling, Constrained Axis Torsional Buckling.

For these reasons, and the one Steve mentioned, I cannot see trying to make DG-25 work for 9th edition steel design.