Isolated footings in non-seismic areas?

[AaronMcD]

Just wondering if this is done and advisable in non-seismic areas. I've done continuous footings, mat slabs, and spread footings integrated with continuous foundations. Working on a project in a non-seismic area and the contractor is thinking continuous frost wall around the perimeter, and isolated footings for interior gravity columns.

 

[JAE]

Done all the time in the midwest USA

 

[phamENG]

Common in the east coast as well. Just be mindful of potential differential settlement.

 

[DaveAtkins]

Depending on the type of building, sometimes wind uplift controls the size of isolated interior footings.

DaveAtkins

 

[milkshakelake]

If the isolated footings are concentric, I don't particularly see why this would be an issue, seismic or not. If the bearing stress under the frost wall and the isolated footings are roughly equal, it should be fine.

I'm not sure what you mean by continuous foundations, though. Like putting two columns on one footing? That's almost the same thing. I guess I don't understand the concern or the question.

 

[BAretired]

Very common detail, usually a square footing under each column.

 

[phamENG]

MSL - in high seismic areas, isolated footings aren't allowed. You have to strap them together to prevent differential lateral movement. (Think of a giant spider on a frozen lake.)

 

[Deker]

Isolated foundations are permitted in high seismic areas as well provided you are Site Class A-D. See ASCE 7-16 12.13.8.2. Even if not required by code, many engineers will dowel the footings to the slab on grade and design the slab on grade as a diaphragm to engage additional sliding resistance.