connecting new and old foundation
connecting new and old foundation
(OP)
Hi, I hope you will help me.
Lets say we have existing foundation in the basement of the house - see attached file.
We want to add another story to building so existing foundations are not wide enough.
We add new concrete foundation and anchor it to existing foundation. How to calculate anchor bars?
Also? if foundation like this are under basement there is a problem because you can only add width to the foundation from the inner side of the basement wall (outer side is under ground). So we get eccentric loading on a foundation (new + old). is that a problem? what to do?
sorry for poor language.
tnx for answers.
Lets say we have existing foundation in the basement of the house - see attached file.
We want to add another story to building so existing foundations are not wide enough.
We add new concrete foundation and anchor it to existing foundation. How to calculate anchor bars?
Also? if foundation like this are under basement there is a problem because you can only add width to the foundation from the inner side of the basement wall (outer side is under ground). So we get eccentric loading on a foundation (new + old). is that a problem? what to do?
sorry for poor language.
tnx for answers.





RE: connecting new and old foundation
RE: connecting new and old foundation
RE: connecting new and old foundation
RE: connecting new and old foundation
is there any other solution than leave it be just as it is or to add width to the foundation from the inner side of the basement wall?
RE: connecting new and old foundation
That width good for 2500 plf at 1500 psf soil bearing. That value should be good for most retail and residential strip footings.
Also, if the maximum stress is due to a point load, remember that you can spread out the load by at least twice the height of the stem wall and strip footing.
Mike McCann, PE, SE (WA)
RE: connecting new and old foundation
RE: connecting new and old foundation
1. Calculate typical load on strip footing in existing condition. Compare against 75 kPa
2. Calculate typical load on strip footing after 2nd storey is added. Compare against 75 kPa
3. If the new load exceeds 75 kPa significantly then I have the client engage a geotechnical engineer to evaluate the soil bearing capacity at three test pit locations adjacent to the foundation walls (normally on the exterior side). Usually not a significant expense.
4. More times than not, in my geographical area, the geotech will come back with 100 or 150 kPa which then justifies the existing footings have sufficient capacity, without any modifications to the footings. It is a bit of a risk, but potential financial rewards are large.
If the footings really did need to be widened, I would underpin the entire footing ... lots of work and expense. I would not accept widening the footing as you have detailed.
RE: connecting new and old foundation
Mike McCann, PE, SE (WA)
RE: connecting new and old foundation
But I cant imagine such a small load on the wall from 2 storey house with wooden roof, brick walls and concrete slabs. Force is more likely between 70 - 120 kN/m which means you need soil of 120 kN/m /0,5 m = 240 kN/m2 = 240 kPa!?
RE: connecting new and old foundation
RE: connecting new and old foundation
I think its mandatory to suggest that to a client... what else can I do.