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RE: FW: 2- way post tension slab

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please look at my blue response texts.
 
 
 
-----Original Message-----
From: Gil Brock [mailto:gil(--nospam--at)raptsoftware.com]
Sent: Sunday, May 16, 2004 3:24 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: FW: 2- way post tension slab
Importance: High

Amir

At 09:07 AM 17/05/2004, you wrote:
Thanks Gail,
 
my fax number is (858-566-0627 ATT:Amir)
 
I am doing strip design in uniformley spaced direction. width of my strip is 28' and my slab thickness is 13.5".
I calculate tendon hight to be 12.5" from bot of slab at point of support.

Are you sure you have sufficient cover to the tendon at this height?  I think for non exposed concrete 3/4" cover should be enough. (UBC 1907.7.3) (please correct me if I am wrong) 

since in my model my support is assumed to be a line and actualy i don't have beam btwn my cols I think my tendon hights should be different in the line of support.
 
what i like to do is to layout my tendon hights like this.
 
12.5" at top of col
10" (or something less than 12.5") at left and right side of my col.

I assume you are saying that the tendons immediately over the column will be at 12.5" and the tendons between the columns will be at a lower level! (yes-between cols in other direction (direction of banded tendons))  And the un-tensioned reinforcement also!  (additional negative reinforcements)(we should have more neg reinf at top of col in column strip than middle strip)
(what i use for design is "Adapt" software which does not assume any middle strip so my strip width is half of my col spacing at each side) 

Why for both?  because if we do a finite element analysis of slab sitting on col. and look at moment diagram we will see max neg moment is immediately at top of cols. so I think I have to reinforce my concrete in proportion to the loads they have to carry. 
 by the way do you agree with the idea of having different tendon heights in line of support?  


Does it make any sence to you?
 
and also I like to do simillar think to my additional req'd reinforcements at top and bot of slab.
 
 
Amir Miraftab
Structural Project Engineer
 
 
-----Original Message-----
From: GSKWY(--nospam--at)aol.com [mailto:GSKWY(--nospam--at)aol.com]
Sent: Sunday, May 16, 2004 12:40 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: FW: 2- way post tension slab

Find someone with a copy of the PTI Design Manual (5th Edition) or go to a university library,  they should have a copy.  Somewhere towards the back of the book, there is a sample layout. Although it is nothing very complicated - there are tendons bands along the column lines in one direction and uniformly spaced tendons in the other direction.  The page in the PTI manual is just a layout - it does not show support heights.

 
If you can't find someone,  give me your fax number and I can fax you that page (although it may not come out that well.)

 
I can't say I would recommend buying the book,  it has a little bit of good information,  but it is way out of date.

 
Gail Kelley

Regards  Gil Brock
Prestressed Concrete Design Consultants Pty. Ltd. (ABN 84 003 163 586)
5 Cameron Street Beenleigh Qld 4207 Australia
Ph +61 7 3807 8022              Fax +61 7 3807 8422
email:          gil(--nospam--at)raptsoftware.com
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