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Re: Flexural reinforcement "Ad Libitum"

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The "exception" that referred back to 10.5.3 was introduced in the 1995
ACI 318.  There is no indication in the commentary as to why it was added.
My guess is that they realized that there was an oversight and that there
is no reason that the 1/3 more than required by analysis provision should
not also apply in seismic situations.  But, in truth that is just a guess
on my part.  Since I know someone on the committee, I will ask and see if
there is a more "detailed" answer (i.e. see if he can tell me the
reason/history).

Regards,

Scott
Adrian, MI


On Sat, 20 May 2006, Syed A Masroor wrote:

> The older versions of the code did not have this exemption. I was trained in
> school on ACI-318-77 when the seismic provisions were in Appendix A. I was
> taught that this omission is intentional, as ductile frames cannot be made
> from plain concrete, even if the member is 1/3 stronger.
>
> I think the exemptional finally crept in the 95 code. I distinctly remember
> designing a building in early 90's on ACI in zone 4 (I usually design in
> zones 1 and 2) and I was made to provide 200/fy in oversized beams. Maybe
> the checker was also an old guy.
>
> Any ACI guru on the list?
>
> Masroor
>
>
>
> ----- Original Message -----
> From: "Scott Maxwell" <smaxwell(--nospam--at)engin.umich.edu>
> To: <seaint(--nospam--at)seaint.org>
> Sent: Friday, May 19, 2006 10:20 PM
> Subject: Re: Flexural reinforcement "Ad Libitum"
>
>
> > Likely because of the maximum reinforcement ratio (the 0.025 value) plus
> > the requirement of at least two continuity bars top and bottom.  Both at
> > "additions" to the requirements of 10.5.3 that are there cause of the
> > seismic "situation".
> >
> > Regards,
> >
> > Scott
> > Adrian, MI
> >
> >
> > On Fri, 19 May 2006, Syed A Masroor wrote:
> >
> > > This is what I had in mind when I wrote this. Somehow, I had always
> thought
> > > it to be this way but when I looked up 21.3.2.1, the 10.5.3 exception
> was
> > > there. So apologies.
> > >
> > >
> > > Any idea why was this limit put in this section again?
> > >
> > > Masroor
> > >
> > > ----- Original Message -----
> > > From: "Scott Maxwell" <smaxwell(--nospam--at)engin.umich.edu>
> > > To: <seaint(--nospam--at)seaint.org>
> > > Sent: Friday, May 19, 2006 2:01 PM
> > > Subject: Re: Flexural reinforcement "Ad Libitum"
> > >
> > >
> > > If it is the section that I think he is thinking about then it would be
> > > section 21.3.2.1 of ACI 318-05, which is basically the same as section
> > > 1921.3.2.1 of the 1997 UBC.  If that is what he is thinking about, then
> I
> > > am not sure why he thinks that the 1/3 provision does not apply to high
> > > seismic zones as that section clearly states that section 10.5.3 (or
> > > 1910.5.3 of the 1997 UBC), which is the 1/3 provision section, still
> > > applies.  Not to mention that that section is only for special concrete
> > > moment frames, which is likely NOT what Joe was dealing with (an
> > > assumption on my part).
> > >
> > > Regards,
> > >
> > > Scott
> > > Adrian, MI
> > >
> > >
> > > On Fri, 19 May 2006 Rhkratzse(--nospam--at)aol.com wrote:
> > >
> > > > Could you save me (us?) some time and give us the code reference?
> > > Thanks.
> > > > Ralph
> > > >
> > > > In a message dated 5/18/06 9:35:23 PM, masroor(--nospam--at)eaworld.com writes:
> > > > > This is not allowed if you are in seismic zones 3 or 4 as per ACI
> > > chapter
> > > > > 21. Were you? Otherwise, the code is quite clear on this issue.
> > > > >
> > > > > Masroor
> > > > >
> > > > > ----- Original Message -----
> > > > > From: "Jesus Gomez" <jgomez(--nospam--at)schnabel-eng.com>
> > > > > To: <seaint(--nospam--at)seaint.org>
> > > > > Sent: Friday, May 19, 2006 2:47 AM
> > > > > Subject: RE: Flexural reinforcement "Ad Libitum"
> > > > >
> > > > >
> > > > > Thank you Joe. That is exactly what I have always used. My submittal
> got
> > > > > rejected by a reviewer on this basis. Go figure!
> > > > >
> > > > >
> > > > > -----Original Message-----
> > > > > From: Joe Grill [mailto:jgrill(--nospam--at)swiaz.com]
> > > > > Sent: Thursday, May 18, 2006 5:41 PM
> > > > > To: seaint(--nospam--at)seaint.org
> > > > > Subject: RE: Flexural reinforcement "Ad Libitum"
> > > > >
> > > > > Doesn't the code allow a 1.33 factor over what steel is required by
> > > > > analysis in lieu of the minimum percentage steel requirements?
> > > > > Joe
> > > > >
> > > > > Joseph R. Grill, P.E. (Structural)
> > > > > Shephard - Wesnitzer, Inc.
> > > > > Civil Engineering and Surveying
> > > > > P.O. Box 3924
> > > > > Sedona, AZ 86340
> > > > > PHONE (928) 282-1061
> > > > > FAX (928) 282-2058
> > > > > jgrill(--nospam--at)swiaz.com
> > > > >
> > > > >
> > > > >
> > > > > -----Original Message-----
> > > > > From: Jesus Gomez [mailto:jgomez(--nospam--at)schnabel-eng.com]
> > > > > Sent: Thursday, May 18, 2006 2:36 PM
> > > > > To: seaint(--nospam--at)seaint.org
> > > > > Subject: Flexural reinforcement "Ad Libitum"
> > > > >
> > > > > I have a "philosophical" question of important implication in a
> current
> > > > > project.
> > > > >
> > > > > I will not use real quantities. Also, I will not describe the
> problem
> > > > > entirely and focus on a particular aspect of it. Say a beam of given
> > > > > dimensions requires minimum reinforcement to handle a given bending
> > > > > moment. Say that the beam is 100 in (d) by 10 in (b) and that the
> > > > > minimum reinforcement is thus 3.33 in2.
> > > > >
> > > > > For constructability, the contractor would need (not prefer) to make
> the
> > > > > beam with d=150 in instead of 100 in
> > > > >
> > > > > Do I need to provide now 4.95 in2 instead of 3.33 in2 ?
> > > > >
> > > > > The typical answer is "yes". However, how can the cracks become
> larger
> > > > > for the same moment, same steel, and a larger section? Also, if I
> keep
> > > > > increasing the size of the section, I would need unrealistically
> large
> > > > > amounts of reinforcement.
> > > > >
> > > > > Just for information, I am retrofitting an existing pile cap with
> > > > > additional piles (micropiles). I am providing a new "pile cap" on
> each
> > > > > side of the existing pile cap connected by dowels, which would work
> as
> > > > > flexural and shear reinforcement at the interface. The dimensions of
> the
> > > > > added pile cap are pretty much defined by external factors and I
> only
> > > > > have a limited space available for dowels.
> > > > >
> > > > > Thank you
> > > > >
> > > > >
> > > > >
> > > > >
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