What are the standards for control joints in concrete??? 2

[innovativeconcrete]

I was wondering what the industry standards are for vertical and horizontal concrete? We believe we may be way overdoing our control joints at 8' for 4" flat concrete and every 12' for 6" concrete. Also, we have lost a job because of our reccommended thickness for a basement foundation wall. We recommended a 12" thick 9' tall wall for a 66' span. Did we overcompensate with concrete thickness? What would you have reccomended?

Sincerely,

Brad Kriegel
General Partner

 

[JAE]

Usually a rule of thumb for joints in slabs-on-grade is 3 to 4 times the thickness. There are good books out there on the design of slabs-on-grade. Specifically I think there is a book by Ringo & Anderson on this. Here's a link to it:

Designing Floor Slabs on Grade

 

[Ron]

Another rule of thumb is 24 to 36 times the thickness (gives the spacing in inches). Your values are not off...in fact they are at the 24x value. If you are going to increase the spacing, be sure that you are tight on thickness control. Keep the thickness variation to -1/4" / +3/8", and the subgrade as flat as possible with no abrupt change greater than 1/2" in about 4 feet. This keeps the "sudden" restraint potential down.

Also, make your joint pattern as nearly square as practicable and with no more than a 1.2 to 1 ratio of length to width.

 

[SlideRuleEra]

Here is "grab-bag" of free resources:

Publications from the "Foundation Performance Association"

http://www.foundationperformance.org/publications.html

US Army Corps of Engineers, "Concrete Floor Slabs Subjected to Heavy Loads"

http://www.wbdg.org/ccb/ARMYCOE/COETM/tm_5_809_12.pdf

National Research Council, "Criteria for Selection and Design of Residential Slabs-on-Ground"

http://newton.nap.edu/catalog/9804.html#toc

The way it is presented, this one takes a lot of patience (download one page at a time)

http://www.SlideRuleEra.net

 

[dik]

I've used JAE's 3 to 4 times the thickness 'in feet' (sorta understood) with 4 times kind of pushing it... The kicker is the timing of the sawcutting and the slump... many contractors don't want to go the extra yard to cut it at the right time... they'd sooner do it the next day... which is likely too late. A real stiff mix is also hard to work with...

Dik

 

[dik]

WRT the wall. It seems a little heavy. Assuming it's reinforced and you're not dealing with expansive soils, you might consider looking at the reinforcing for an 8" wall thickness. You might be able to provide suitable backfill to reduce lateral pressures.

Dik

 

[archeng59]

PCA has a handbook, "building movements and joints", that has some good information.