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PTI Design Method, was RE: Have you heard of watering your foundation?

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I would really, really like additional comment on the PTI design method vis-à-vis its scientific underpinnings. This is a subject I have always been deeply interested in and I have always wondered what others think of it.


I will start the discussion by offering that the two competing design methods (BRAB and WRI/Snowden) are empirically based.


Eric Green


-----Original Message-----
From: GSKWY(--nospam--at) [mailto:GSKWY(--nospam--at)]
Sent: Monday, November 18, 2002 11:00 AM
To: seaint(--nospam--at)
Subject: Re: Have you heard of watering your foundation?


In a message dated 11/18/2002 11:48:58 AM Eastern Standard Time, Bruce.Trobridge(--nospam--at) writes:

I was asked this question by my brother who is building a house in the Dallas area

I am guessing that it is a post-tensioned slab on grade, built on expansive soil, and that he is referring to the PTI emphasis on "foundation maintenance"  which involves keeping the moisture content around the foundation constant to avoid cracking the slab.  

Although this may be a good recommendation, it is probably not the reason there is so much cracking in post-tensioned slabs on expansive soils, and even if your brother diligently waters his rose-bushes, he is likely to get some cracking.

The PTI design method is wildly unscientific,  the slab will almost certainly crack less if it is post-tensioned but it is still very likely to crack, based on past performance of these slabs.

Gail S. Kelley, P.E.