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Re: IBC LL Reductions/2003 IBC Question

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Paul,

>From what I can tell, section 1607.9.1.x LL reduction is essentially
directly from ASCE 7-98.  This is very similar to what has been in the
BOCA code for a while and is in the 1997 UBC as the alternate LL reduction
(with the exception that both the BOCA and UBC alternate use Ai instead of
At*KsubLL, but is basically the same).

Section 1607.9.2 is the same as the primary LL reduction method in the
1997 UBC.  And the UBC is rather specific in that it does permit reduction
of LL on parking garages up to a limit of 40% (see the last paragraph of
section 1607.5 of the 1997 UBC).

Now, the interesting thing is that the alternate LL reduction section in
the 1997 UBC (which is basically like section 1607.9.1 of the 2000 IBC)
does not take away the LL reduction for parking decks.

As a result, I think that you have pointed out an inconsistancy in the
IBC.  As section 1607.9.1 is basically from ASCE 7-98 (which does not
allow LL reduction for parking decks except for limited cases), it mirrors
the requirement on not permitting LL reduction for parking decks.  Section
1607.9.2, however, appears to have been taken from the 1997 UBC code
directly, which DOES allow for LL reduction for parking decks.  Thus, it
appears that when the IBC folks took the UBC method for their alternate LL
reduction method, they seemingly did not coordinate it with what they had
as the primary LL reduction method from ASCE 7 when it came to what is
permitted and not permitted for parking decks.  At least that is how it
appears to me...but I might be missing something.

And, no, I don't know how the 2003 IBC handles the issue.

HTH,

Scott
Ypsilanti, MI


On Mon, 16 Dec 2002, Paul Crocker wrote:

> Looking at the 2000 IBC, I have noticed that they have two different sets of
> equations for LL reduction.  A set of equations that I assume is the old
> BOCA equations is in 1607.9.1 and a set that is the old UBC equations is in
> 1607.9.2.  In 1607.9.1.2 they take away LL reduction for most parking garage
> applications.  In 1607.9.2, which is states that is is an alternate for
> 1607.9, there is no such limitation on parking.  How are designers and plan
> checkers approaching this?  Does one simply use the 1607.9.2 equations if
> one wishes to use LL reductions in parking?  Does anyone know what the 2003
> IBC does with this section?
>
> Paul Crocker, PE, SE
>
>
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