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RE: Chairs for Placement of Post-Tension Cables in Slab

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No, it’s very common. In fact, Ringo & Anderson’s book “Designing Floor Slabs on Grade” (see discusses post-tensioned residential slabs, in chapter 8, and their example uses a 4” slab.


The slab is a sort of “waffle” slab with stiffening beams at regular intervals in both directions. In addition to the slab tendons, each beam has a tendon near the bottom of the stem.


Keep in mind that the effective stress in such a slab is rather low—the old PTI manual recommends 50 psi, many engineers insist on 100 psi, I split the difference and use 75 psi). The idea is a “stiff slab,” wherein stresses induced by ground movement are only one consideration.


From: Stanley E Scholl [mailto:sscholl2(--nospam--at)]
Sent: Monday, August 30, 2004 10:47 AM
To: seaint(--nospam--at)
Cc: seaint(--nospam--at)
Subject: Re: Chairs for Placement of Post-Tension Cables in Slab


I have never heard of post tensioning a 4" slab on grade. The people who do this for a living in our area use 8" slabs.