Existing Building Footer Capacity

[vmirat]

I have a project to build out an existing second story patio for additional office space. The as-built drawings for the building indicate that the allowable soil bearing capacity used for design was 2000 psf. The existing building is about 20 years old.

Does the bearing capacity of an existing footer increase over time?

 

[msquared48]

If settlement occurs and stabalizes, then, technically, the capacity increased during the settlement to the point of equalization of forces. However, I would not use this as it is not readily quantifiable.

When the building was designed, more likely than not, no soils report was done or available, so the 2000 psf was an allowed design value under the UBC at that time. Things have changed and that value is now more in the 1500 psf range.

If you need a higher value, your best bet is to engage a Geotech and get a soils report.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[vmirat]

The footer in question is an interior column of an office building, so checking the soil is out of the question. The building design included a geotech report, so the 2000 is what they determined.

 

[msquared48]

Then either use 2000, or get another report.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[JAE]

Or underpin the footing.

 

[MiketheEngineer]

Agree w/ M^2 - and many times the footing was poured bigger than specified.

If you can pull up or remove the floor treatment - drill thru the slab and try to get the size of the footing. You might get lucky - might not.

 

[oldestguy]

Or the 2,000 was "conservative". Guess I can use that word here, Huh?