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RE: Point Loads on Strip Footings

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A couple of thoughts: 

1) Distribution over a width of footing equal to 1/2 the wall height seems
very conservative, although you may certainly want to be careful if your
wall is not very competant.  Can you reasonably take more than that?  Is the
point load really a "point" load, or does it have several feet of width that
you can take advantage of?  

2) Not knowing where you are located, it is impossible to guess, but 3.5 ksf
is not unreasonable for a good soil.  Unless you know you are on bad soil or
fill, and thus probably a lost cause, you may want to talk to a local
geotech and see if you can get a better idea of the capacity.  A brief soils
report might be cheaper than doing a retrofit.  

Paul Crocker, PE, SE

-----Original Message-----
From: npitera(--nospam--at)mmm.com [mailto:npitera(--nospam--at)mmm.com]
Sent: Wednesday, August 21, 2002 1:08 PM
To: seaint(--nospam--at)seaint.org
Subject: Point Loads on Strip Footings





A strip footing that supports a masonry block wall there is the potential
for
adding about 11 kips of point load at the top of the masonry wall. For load
distribution, I think I can take up to 1/2 the wall height which would be
4'-6".
With the 11kip load spread over 4'-6" feet, the  future bearing pressure be
3.5
ksf from about 1.0 ksf. The  allowable soil bearing capacity is unknown, the
building is about 50 years old and shows no signs of settlement.

Typically, when the allowable bearing pressure is unknown, I try to keep the
bearing pressure below 2.5 ksf. I would hate to underpin the strip footing
and
place a spread footing for fear of the a sudden settlement, or screw up by
the
contractor. I think that underpinning a standard strip footing may be a cure
that is as risky as the disease.
Doweling into the side of 12" thick strip footing to enlarge the footing I
think
is just as risky.

Are there any other options?

I would appreciate any comments on this issue.
 I thank you in advance.

Regards,

Nick.




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