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# Re: ACI 318 11.4.2.2 - Defintion of Vp in Eq. 11-12 (Prestressed Concrete Design for Shear)

• To: <seaint(--nospam--at)seaint.org>
• Subject: Re: ACI 318 11.4.2.2 - Defintion of Vp in Eq. 11-12 (Prestressed Concrete Design for Shear)
• From: Scott Maxwell <smaxwell(--nospam--at)engin.umich.edu>
• Date: Fri, 8 Nov 2002 19:18:49 -0500 (EST)

```Bill,

Yes...your interpretation is consistant with my understanding.

And my text book on prestressed concrete (by Naaman) would concur with you
that it is not a trival thing to compute.  From my text book:

"The computation of the values of vci and vcw, given by the above
expressions, is time-consuming, especially as several sections along the
span must be considered."  (Note that Eq 11-12 is what is being referred
to as vcw)

My text book then proceeds to point back to the fact that if fpe is not
less than 0.40*fpu, then you can use Eq 11-9, but I am assuming that that
is not an option for you since you are asking the question.

You also have the additional alternative that appears right after eq
11-12...some blather about principle tensile stress of 4*sqrt(f'c) at the
centroidal axis of the member when under the dead load plus live...blah,
blah...it was making my head hurt, so I was not willing to try and sit
down to figure out specifically what it meant at this point.  Hell, it is
FRIDAY night!!

HTH,

Scott
Ypsilanti, MI

On Fri, 8 Nov 2002, Bill Polhemus wrote:

> This is not clear to me at all, nor can I find any design examples that
> directly address it. It seems to require that at each section you are
> investigating, you compute the slope of the tendon, and then get the
> vertical component of the prestress force (adjusted for losses).
>
> But this is NOT a trivial thing to compute, especially when you have a
> complex tendon profile.
>
> Am I missing something here?
>
> Anyone who can comment, please feel free.
>
>
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