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RE: In-Slab Ducts in P/T Slabs

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Title: RE: In-Slab Ducts in P/T Slabs


We have designed a number of projects with duct systems embedded in the floor slabs.  In fact, if my memory is correct, we possibly designed the first such project in the U.S. many years ago.  It involved Walker duct embedded in the slabs of a P/T concrete joist (wide pan) floor system.  Our experience with this over the years has been both good and bad.  I offer two cautions:

*  Pay attention to fire code considerations.  For example, if the ducts do not have sufficient concrete cover (top and bottom), the fire resistance rating of the floor assembly can go way down.

*  Make sure that the owner has a good concrete contractor if he wants flat floors.  The ducts, especially the headers or trunks, can make high F numbers very hard to achieve.


Stan R. Caldwell, P.E., F.ASCE
8616 Northwest Plaza Drive
Dallas, Texas  75225
Phone:    (214)346-6280
Mobile:   (214)236-9696
Fax:      (214)739-0095
Email:    scaldwell(--nospam--at)   

-----Original Message-----
From: Jeff Creagan [mailto:jeffc(--nospam--at)]
Sent: Friday, July 30, 1999 11:28 AM
To: SEAOC Listserver
Subject: In-Slab Ducts in P/T Slabs

We have been asked on several recent projects about the feasibility of introducing in-slab mechanical ducts (i.e. 2" x 12") into our flat plate post-tensioned concrete slab design.  Apparently, this is a system that is very common in Canada, where they are utilized in conventional mildly reinforced slabs.  Any opinions?