Adding pad footing to existing strip footing

[mcbooya]

Hello,

I am looking for advice on adding a footing for a post load that is being added to an existing interior basement strip footing. The point load of 7kips would require a 12" width strip footing length of 7' on its own since it is unreinforced. If I pour a footing extension on both sides of the strip footing and dowel it in can I treat the combined strip+extension as a combined area for the new loading condition? Any other concerns to think about?

 

[KootK]

The point load of 7kips would require a 12" width strip footing length of 7' on its own since it is unreinforced.

That doesn't sound so bad given the likely load spread down through a normal height concrete or masonry bearing wall.

f I pour a footing extension on both sides of the strip footing and dowel it in can I treat the combined strip+extension as a combined area for the new loading condition?

That's almost impossible to do when you look at the anchorage / bar lap requirement properly.

If you really need localized bearing capacity beyond what the strip footing can do with load spread, some form of underpinning might be a good option.

 

[SE2607]

That doesn't sound so bad given the likely load spread down through a normal height concrete or masonry bearing wall.



That's almost impossible to do when you look at the anchorage / bar lap requirement properly.

If you really need localized bearing capacity beyond what the strip footing can do with load spread, some form of underpinning might be a good option.

I like an 5' sq. underpinned pad better than a 1' x 7'. Sure, underpinned pads are hard to do, but the continuity of reinforcing KootK refers to is the biggest problem to me. It's like trying to expand an overloaded pad footing by pouring around the perimeter and doweling into the existing pad footing. Enticing, yes. Good idea, no.
If you are in California, the CBC allows 1,500 PSF w/o a soils report. If you have a soils report limiting you to 1,000 PSF, I would question the geotech about that. If you could use 1,500 PSF bearing value, that underpinned pad becomes 2'-3" sq.

 

[XR250]

I usually just put the pad under the existing strip footing. The excavator can get about half of it, the laborers the rest.
Even if the numbers work out, I avoid doweling into footings as it is never done properly.