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RE: ACI 318 11.4.2.2 - Defintion of Vp in Eq. 11-12 (Prestressed Concrete Des...

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The problem here is that we are investigating a BEAM section where the tendon profile is seriously screwed up.
 
I actually call it "the wave".
 
The layout folks screwed up, and instead of a small reverse parabola at one end of the beam, they put in a "double reverse" in the last eight feet of a 63 foot beam. Since this is an indeterminate moment frame, moreover, the prestressing (post-tensioned) effects are not trivial in assessing the structure.
 
In this case, we need as much shear capacity from the existing concrete as we can possibly get. Conversely I want to make sure that we don't assume more capacity than actually exists.
 
I am curious about the sign of Vp. It seems to me that, if you have a "screwed up" tendon profile, as we do, that Vp could actually REDUCE the total capacity due to Vcw.
-----Original Message-----
From: GSKWY(--nospam--at)aol.com [mailto:GSKWY(--nospam--at)aol.com]
Sent: Friday, November 08, 2002 7:37 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: ACI 318 11.4.2.2 - Defintion of Vp in Eq. 11-12 (Prestressed Concrete Des...

Note that although the recommendation to ignore Vp is in the section for slabs, it also applies to post-tensioned (i.e. cast-in-place) beams.

For post-tensioned beams,  Vc is always calculated by Eq. 11-9.

Gail S. Kelley