Basement Footings

by Robert Mills
(Indianapolis, Indiana)

Question:

I am remodeling a basement and have to support two columns which are schedule 40 rated for about 20,000 Pounds Each.

I am installing a light steel beam that is 17 feet long with a free span of 16 Feet.

The Beam and Column Companies are telling me I am going to have approximately 13,000 pounds point loaded on each column at the ends.

What is the appropriate method for cutting the concrete slab back and installing support for the columns?

Answer:
Hi Robert,
The best way to demo your floor is to saw cut slab to the dimension of the footing needed for the column. To determine the size of the footing that you need take the 13,000 pounds and divide by 1500 psf(assumed allowable soil bearing pressure). The answer is 8.7 square feet, a 3ft x 3ft footing will provide 9 sq feet footing.

Saw cutting will not only provide even edges at the perimeter of the new footing, it will prevent damaging slab beyond where you intend to work. The disadvantage of saw cutting it cost money to hire a company to do the saw cutting. If the floor slab is going to be exposed, saw cutting is a must.



Since a sledge hammer or jack hammer will be needed for this demo, why not just use that and don't bother with saw cutting. If the floor finish is going to be something else other than exposed slab, the final outcome of the slab joints do not matter. I would prefer this route because of the saving in saw cutting.

Detail 28 above shows how the fix should look. As shown the footing needs to be much deeper than the existing slab. Make sure the column is long enough to accommodate the footing to steel column connection. The top of the anchor bolts must be below the new slab pour back by about 2 inches.

Good luck