Residential spread footings rebar

[RustyTools]

I have to add 2 spread footings to the center of my house, one to hold 9,000 lbs and the other 23,000 lbs. I have a spread footings design using a rebar size I can't get, so I am looking for advice on how to do the footings using 1/2" diameter rebar.

The soil capacity is 3000 psf. The footing for 9000 lbs will be 2'x 2' and the footing for 23,000 lbs will be 3' x 3'. Both would be 1' thick. What would you recommend for spacing for 1/2" rebar?

Thanks

 

[RockEngineer]

Most interior footings like that end up with 1/2" rebar on a 12" grid. This is usually very conservative.

 

[GeoPaveTraffic]

RustyTools,

What was the rebar size and spacing in the design that you have? With that information, it would be relatively easy to come up with an equivilant design.

 

[DaveAtkins]

The 2' X 2' footing works unreinforced. The 3' X 3' footing works with (4) #4 bars each way.

DaveAtkins

 

[RustyTools]

The original design was #5 rebar 12"O.C. That was done by rule of thumb, not by calculation. The 3000 psf is based on coarse, granular sand and that the builder built the rest of the neighborhood based on that

 

[GeoPaveTraffic]

To get the same area per unit width of footing the 0.5 inch (#4) bars need to be installed every ~7.5 inches. Since the original design was based on "rule of thumb" this is probably more than you need, however, in this case more is better.

 

[SperlingPE]

Any soil problems with using a 2'x2' square footing?

 

[GeoPaveTraffic]

That depends on the type of soil, magnitude of the load, and the tolorance of the structure for settlement.