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Re: General Building Code Question

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Mike,

As I mentioned to Jake in my more recent post, the committee did have a
reliability (i.e. probability/statistical study to determine appropriate
phi/load factors) study done.  This study was the basis for them feeling
more comfortable with the apparently less conservative design in the
318-02.  Considering the guy who wrote the text book that I used in school
(MacGregor) and the guy I learned concrete from in school, who is now the
318 chair (Wight), and many others of similar concrete knowledge seem to
feel comfortable with the change and the new data that backs up the
change, I am not in too much of a hurry to second guess them.  Add to
that, the person incharge of doing the new reliability study was the guy
who taught my relibility course in school (Nowak...see reference 9.9 in
ACI 318-02 for the study).

HTH,

Scott
Ypsilanti, MI


On Wed, 30 Oct 2002, Michael L. Hemstad wrote:

> Scott Maxwell wrote:
> >>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.
>
>
> They aren't the same.  318-99 Appendix C had considerably lower phi
> (strength reduction) factors to go with the lower load factors.  318-02,
> in mainstreaming the lower load factors of ASCE-7, jacked the phi
> factors back up to previous levels, resulting in considerably less
> conservative designs.
>
> Considering the rather pompous argument made in the last paragraph of
> the 318-99 Appendix C Commentary, I was very surprised to see the abrupt
> about-face 318-02 made in raising the phi factors back up to previous
> values.
>
> Mike Hemstad
> TKDA
> Saint Paul, Minnesota
>


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