What is the outside #4 hoop dimension for 42 inch square column?

[califdirtguy]

To all - I am managing the installation of 42-inch square footing pedestals for a small substation. A very large and reputable reinforcing steel company detailed the outside dimension of the hoops as 38-inches square. All the site steel has been detailed assuming the outside clearances are at minimums. While the hoops hold the 38-inch dimension well, we are fighting a lack of 2-inch clearance to the face of the steel forms on just about every footing. Some footings, we are lucky if we get 1-1/2 inches clear.

Was this a mistake? Should the hoops been detailed for 37 or 36 inch square?

 

[Ron]

If the inside of your form dimension is 42 inches and your cage outside dimension is 38 inches, you should have 2" clear on each side. Check your measurements. If the cage is holding at 38", then the inside of the form dimension must be incorrect or the cage is not centered in the form or the form is not centered on cage!

 

[FlashSet]

Sounds like the 38" is measured to the centerline of the #4 hoops.

 

[msquared48]

Ron:

I thought it was 1.5" clear to the ties. That would give 39".

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[BAretired]

In Canada, the minimum cover for ties is 50 mm (2") when concrete is cast against a form and the surface is exposed to earth or weather. If it is not exposed to earth or weather, the required cover is 40 mm (1.58").

A 38" outside dimension for stirrups provides 2" clear cover and would be standard steel detailing practice. But even if the cover in some locations is as low as 1-1/2", there is nothing much to worry about.

BA

 

[msquared48]

BA is right. I was thinking inside. Exterior exposure is 2". So 38".

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[wannabeSE]

ACI 318 requires 1.5" cover for #5 and smaller bars exposed to weather. The 2" cover is for #6 and larger. It sounds like califdirtguy may be having problems with the ties being centered in the form.

 

[califdirtguy]

Thanks for the replies so far - The contractor is using one of the square ties as a bottom template to hold the vertical dowels and to help place the remainder of the ties. (His crew also lifts the template up after the ties are finished.) But once the base concrete is placed and he is ready to place the pedestal forms, his clearances are comprised. We checked one reinforcement cage he is fabricating on the ground and it suffers the same problem without the concrete - the out to out dimensions of the finished ties are greater than 38 inches.

Again the question remains whether using 38 inches as the out-to-out tie dimension requires near perfection to maintain even a minimum 1.5 inch clearance (2 inches minus a 1/2 inch placement tolerance.

 

[Ron]

Mike...agree....his question had nothing to do with code, just geometry.

 

[BAretired]

In a 42" x 42" pedestal, there are bound to be more than four vertical bars, so the idea of using one square tie 38" x 38" outside dimension is not sufficient to properly tie the bars. Each bar in the face requires a right angle bend which means you should be using rectangular ties 38" in length but less in width. This would tend to maintain the 38" maximum out to out dimension.

But it does require very accurate placement to maintain a 2" cover on each of the four sides.

BA