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RE: General Building Code Question

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As long as we are on this topic, let me ask a question.  The phi factors are
different for the different load combinations (ACI vs. ASCE).  The IBC and
UBC both want you to use their load combinations for seismic loads.  What
phi factors do you use?  Do you use the ones consistent with ASCE because
that is where the load combinations come from or the ones from ACI because
the load combinations are "in addition" to the ACI combinations?

Jake Watson, P.E.
Salt Lake City, UT

P.S.  The phi factors are different in 318-99 and 318-02 for the ASCE load
combinations.  In my mind they should still be the same as in 318-95.  The
strength of the elements didn't change, just the way we calc the loads on
the elements.

-----Original Message-----
From: Scott Maxwell [mailto:smaxwell(--nospam--at)engin.umich.edu]
Sent: Wednesday, October 30, 2002 12:01 AM
To: seaint(--nospam--at)seaint.org
Subject: RE: General Building Code Question


Jake,

FYI, ACI 318-02 has been adopted by the 2003 IBC...at least that is what I
understand.  I don't know what "tweaks" they may or may not have done, but
they shold be rather few.

Regarding, the changed load factors and the unified design...using them
with ACI 318-99 is not in violation of that code.  Those provisions ARE in
the 1999 ACI 318 (and the 1995 ACI 318 as well), but are just contained in
Appendix B and C.  Thus, unless the model building code that references
ACI 318 strictly states an exception for the use of the Appendicies, then
you are certainly permitted to use those provisions.  I had mentioned them
mainly because they are now in the main body of the code in the 2002
edition and as a result will become used on a more main stream basis.  Of
course, if you like things the "old" way (i.e. 1.4 for DL, 1.7 for LL, 0.9
for flexural phi, etc), then you can still design that way with ACI 318-02
since they are still in the 2002 ACI 318...just they are now in Appendix B
and C.

The only thing that you cannot do in 2002 ACI 318 that you could do before
is use the alternate design procedure (working stress).  It is no longer
present in the code.  The committee did bow to some pressure and put in a
statement in the commentary for section 1.1 that says taht you can still
use the working stress design method of the 1999 ACI 318.  Technically,
however, this is worthless since it appears in the commentary, which has
as much legal authority as you or me wirting it on some toilet paper and
saying it is part of the code.  Now before anyone gets there panties in a
bunch, working stress design _IS_ still included and permitted in the ACI
350 code.  Thus, in the future if you are designing water retention
structures where a work stress design is more traditional and desirable,
you should likely be using the ACI 350 code and will be able to still use
the WSD.

HTH,

Scott
Ypsilanti, MI


On Tue, 29 Oct 2002, Jake Watson wrote:

> Just to play devils advocate, you must also consider that the IBC did not
> have an opportunity to change the 318-02 provisions.  The IBC does make
> changes to 318-99 and there is no guarantee that IBC '03 will accept the
> changes made in 318-02.
>
> That said, I have personally used the precast wall panel provisions in
> 318-02 because they make a lot more sense than the ones in the 2000 IBC.
I
> have also adopted the new phi factors and load combinations.
>
> On another note, I have to agree with the other statements about cracking
in
> PT slabs.  I have only worked on two of them, but I would be very careful
> before using the higher values.  Cracking over / around columns is very
hard
> to predict with all the steel and tendons being placed there.
>
> Jake Watson, P.E.
> Salt Lake City, UT
>
> -----Original Message-----
> From: Cliff Schwinger [mailto:clifford234(--nospam--at)comcast.net]
> Sent: Monday, October 28, 2002 9:23 PM
> To: seaint(--nospam--at)seaint.org
> Subject: General Building Code Question
>
>
>
> This is a general question but I will ask it by giving a specific
> example.
>
> IBC 2000 references ACI 318-99 for concrete design.  Does the reference
> to ACI 318-99 mean that engineers are bound to using this specific
> edition of ACI 318?  For most aspects of concrete design it does not
> make much of a difference as to which edition of ACI 318 is used;
> however sometimes there some significant differences between the new and
> old editions that can have an impact on member design.
>
> Here is why I am asking:
>
> ACI 318-02 allows flexural tension stresses in post-tensioned flat
> plates to be as high as 7.5 x (f'c)**0.5.  Prior to ACI 318-02 the upper
> limit on this value was 6 x (f'c)**0.5. Since IBC 2000 specifically
> references ACI 318-99, I am assuming that engineers are not permitted to
> take advantage of the higher service level tension stress.
>
> Am I correct with this assumption?
>
> Thanks.
>
> Clifford Schwinger P.E.
>
>
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