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RE: Control Joints in a Mat Foundation

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According to Bill’s criteria the joints would appear to be at 48’ oc, that is, 3x16 in feet.

 


From: Daryl Richardson [mailto:h.d.richardson(--nospam--at)shaw.ca]
Sent: Thursday, October 27, 2005 3:29 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: Control Joints in a Mat Foundation

 

Ralph,

 

        If you're confused so am I.  I understand the question to suggest that the specified joints are spaced a 3T centers or 3*16 = 48" or 4'- 0" o/c.  This close spacing seems quite unrealistic to me.  In the past I've used foundations like this for manufactured buildings 30' by 50' with no joints at all; no problems were ever reported to me for these buildings.  I don't believe these joints are required at all unless the building is much larger than I am envisioning.

 

Regards,

 

H. Daryl Richardson

----- Original Message -----

Sent: Thursday, October 27, 2005 2:21 PM

Subject: Re: Control Joints in a Mat Foundation

 

I'm a little confused.  Presumably you're using a mat fdn. because you need the *whole* foundation to act together and distribute loads throughout the building footprint.  (I'm assuming a "normal" size building, not a Wal-Mart-size building.) 

I also assume you have "decent" rebar in 2 mats, top and bottom, maybe #5 @ 12" oc EW or so.  I don't know why you would want to have any sort of weakened joints in such a foundation.  It seems to me that that would be like putting shrinkage joints at midspan of a beam.   Don't you need the full strength of the mat at all locations? 

Or maybe I misunderstand the situation.

Ralph Hueston Kratz, S.E
Richmond CA USA

In a message dated 10/27/05 12:29:41 PM, T.W.Allen(--nospam--at)cox.net writes:


I am working on a project which consists of a single story wood framed building sitting on a mat foundation. The mat is 16” thick.
 
A field question has come up regarding control joints. In a typical slab-on-grade, I specify cuts one third the slab thickness spaced no more that 3T feet where “T” is the slab thickness in inches. These recommendations don’t make a lot of sense for a 16” “slab”.
 
What would be a more appropriate guideline for this situation?
 
TIA,
 
T. William (Bill) Allen, S.E.
ALLEN DESIGNS
Consulting Structural Engineers