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RE: Thickened Edge Slab - Jointing

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I’m resending this because my font for fractions got changed in the email.  The 1/2 symbol became an = sign

 

Dave,

 

First, I don’t know anything about the environment.  If this is a building slab with normal use then it is very easy.  If it is a freezer building then it is something different.

 

I will explain what I do for a typical warehouse or retail building.

 

Joint spacing should not exceed the 3*T value.  In your case it is 18 feet.  That is where I start.  I then divide the slab dimension by 18 to come up with the number of panels.  In your case it is 2 panels by 4 panels.  Now here is where it gets confusing.  The first panel is 1/2 and the last is 1/2  in size.  The reason it is 1/2 in size is the turned down edge becomes an anchor point, the point of zero movement.  If you were to mirror a factitious slab outside the building with the center located on the turned down slab section, that is how the flat slab with no turn down edges would behave.  It is also how this slab will behave since it is anchored at the edge.  So the distance to the first joint must be 1/2 the typical spacing.

 

So here is the spacing of the joints I would use;

7.5 ft., 15.0 ft., 7.5 ft.

7.5 ft., 15.0 ft., 15.0 ft., 15.0 ft., 7.5 ft.

 

These can slide some if for some reason it is better not to use the exact numbers.

 

If you are using a pre-engineered metal building then I like to adjust my joint spacing so the joints do not fall on a column line.  For light thrust loads I use a hairpin and I like as much continuity of the slab reinforcing as possible spanning between the rigid frames.  Depending on the rigid frame spacing, I locate the joint midway between the rigid frames or at 1/4  points between frames.

 

You can only get away with no control joints if you add reinforcing to handle it, or you use shrinkage compensation.

 

HTH

 

Rich

 

 


From: David Maynard [mailto:DMaynard(--nospam--at)kfx.com]
Sent: Wednesday, September 06, 2006 4:02 PM
To: seaint(--nospam--at)seaint.org
Subject: Thickened Edge Slab - Jointing

 

Here’s what I got.

 

It’s an insulated, reinforced, thickened-edged concrete floor slab.  It’s 30 ft wide, about 60 ft long, and 6 inches thick in the middle, with the edge thickness of 24 inches.

 

Should I put in control joints???  If so, at what spacing???  Is there a way I can get away with no control joints???

 

The thing that is throwing me off is the thickened edge (I know what to do with a regular flat slab).  Any help would be greatly appreciated.

 

Dave Maynard, PE

Gillette, Wyoming