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Re: IBC Sec. 1605.3

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Jason:

I would say that she is right, but then your are not wrong either, rather
just conservative.  I would say that the exception DOES apply to the load
combination in eq 16-17 such that snow loads need not be added as part of
the load combination if less than 30 psf.  The point is, however, that is
DOES NOT say it "will not" included, but rather that it "need not" be
included.  Thus, you are still correct in including the snow loads, but
you are being overly conservative _AND_ she is right in NOT adding the
snow load effect.

Note that ASCE 7 _DOES_ take your position...in otherwords, there is no
exception in ASCE 7 for either Allowable Stress or LRFD load combinations.
And since BOCA tended to used ASCE 7 in this area with little or no
modification, it to did not have such an exception.  The 1997 UBC does,
however, have such a provision.  Thus, this exception seems to be a legacy
provision from the 1997 UBC, which admittedly is not used too much in
moderate snow climates (i.e. the Midwest) but is used where some severe
snow could occur (i.e. mountainous areas of CA, etc) which would make the
exception moot.

The end result is that it appears that it would be left up to the EOR to
decide if they want to be conservative or not (unless the model building
code is modified in some way by the local jurisdiction...Michigan makes
some changes to the IBC when it adopts it).

HTH,

Scott
Ypsilanti, MI


On Fri, 12 Sep 2003, Jason Kilgore wrote:

> First, thanks to everyone who responded to the seismic question.  Especially
> thank you for agreeing with me.  :)
>
> Now I have a new question dealing with the ASD load equations, and I think I
> might be wrong on this one.  But at least I was conservative.
>
> I was checking someone else's work, and she did not include snow loads (Pf =
> 25 psf) in equation16-17.  Her argument was Exception 2, which says that
> snow loads less than 30 psf need not be combined with seismic.
>
> I always took this to mean that the WEIGHT of the snow does not need to be
> added to the weight of the structure used to calculate base shear.  This is
> stated clearly in section 1617.4.1 paragraph 4 under the definition of "W".
> However, you WOULD include snow loads on the actual beams being designed.
> The fact that this exception isn't listed under the LRFD equations is an
> additional argument for my side.
>
> What say you guys?
>
> ----
> Jason Kilgore
> Leigh & O'Kane, L.L.C.
> jkilgore(--nospam--at)leok.com
> 816-444-3144
> 816-444-9655 (FAX)
>
>
>
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