Evaluating Existing Spread Footings
Evaluating Existing Spread Footings
(OP)
I am evaluating some existing spread footings for possible increased capacity.
The original drawings show a few locations where the bearing pressure is 9000 psf.
This seems extremely high.
When I check the existing footings for increased loads I am getting numbers in the 10,000 psf area. The footings would have to be on bedrock to satisfy these conditions and I am quite certain the building is not on bedrock which makes the original value of 9000 psf on the drawings seem absurd as well.
What were engineers using for allowable bearing values in the 1940's?
Is there any chance a soils test was done as this time?
Without a soils test now, am I ok to use the presumptive values of IBC Table 1806.2?
Does a soils test even help in evaluation of existing footings?
The original drawings show a few locations where the bearing pressure is 9000 psf.
This seems extremely high.
When I check the existing footings for increased loads I am getting numbers in the 10,000 psf area. The footings would have to be on bedrock to satisfy these conditions and I am quite certain the building is not on bedrock which makes the original value of 9000 psf on the drawings seem absurd as well.
What were engineers using for allowable bearing values in the 1940's?
Is there any chance a soils test was done as this time?
Without a soils test now, am I ok to use the presumptive values of IBC Table 1806.2?
Does a soils test even help in evaluation of existing footings?






RE: Evaluating Existing Spread Footings
If not, then, assuming these footings were loaded as designed, perhaps the original data is good.
If there is damage, then the deduction is obvious.
I assume that the footings are in a confined location?
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: Evaluating Existing Spread Footings
RE: Evaluating Existing Spread Footings
The short answer is, yes, the building shows signs of distress that I am assuming are the result of differential settlements.
This leads to another question I guess...
A considerable amount of the loading on the columns is from overhead cranes. In some cases, the crane loading can double the foundation load. Should I be considering this crane loading as transient when combined with D & L loading?
RE: Evaluating Existing Spread Footings
I also agree with JAE, but I am also concerned about the distress, not necessarily caused from overloading, but perhaps from vibration.
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: Evaluating Existing Spread Footings
I get very reasonable bearing pressures without the crane loading.
Following the combinations I typically check with cranes now, they arent even close.
One combiantion in particular is simply DL + LL + Live Roof + MULTIPLE CRANES.
This combination is a killer, but is also not very likely to occur very often.
RE: Evaluating Existing Spread Footings
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: Evaluating Existing Spread Footings
Are these the original cranes placed in the building. Maybe someone upgraded the cranes and never bothered to check the footings?
RE: Evaluating Existing Spread Footings
I am 100% certain that the foundations were never upgraded.
SteelPE-
Thank you for the note.
I thought I had seen this before, but I am often forced to use load combinations by AIST also.
RE: Evaluating Existing Spread Footings
RE: Evaluating Existing Spread Footings
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: Evaluating Existing Spread Footings
Owners of these buildings more often than not just proceed to beat the hell out of the building as long as product is going out the door.
They also love to call when something is just about to collapse and ask "how could this happen!?".
To which I usually reply "Well, when an inspection or analysis shows items that are grossly deficient and there was a recommendation to fix or replace the item.....
RE: Evaluating Existing Spread Footings
If you are running into differential settlement on the crane lines I imagine the would be putting unnecessary wear on their cranes..... which I imagine are not easy or cheap to fix.
If they are having problems with premature wear..... maybe you could approach the client and say that this will help them "get more product out the door" because they should not have to fix their cranes as much. Down time now means less down time in the future.
Also, how would adding more columns help with the footing problem? Unless the spans are large adding more columns might not have the desired effect.
RE: Evaluating Existing Spread Footings
Its just like many old early 1900's industrial buildings. They are beat up. They seen their useful life IMO. There is many more problems than the settlements which themselves are rather apparent by simply looking down the runway girders and seeing the up and down.
The cranes do see unnecessary wear from the structure being out-of-tolerance, if you will. Fixing these structures is not cheap or easy. There is often machines, foundations, piping and utilities all over the place, etc. Even simple structural steel reinforcement can be a real challenge at times.
The line about new columns and footings was more or less a joke as it is simply not feasible.
RE: Evaluating Existing Spread Footings
RE: Evaluating Existing Spread Footings
RE: Evaluating Existing Spread Footings
RE: Evaluating Existing Spread Footings
RE: Evaluating Existing Spread Footings
RE: Evaluating Existing Spread Footings
RE: Evaluating Existing Spread Footings
The footings were fairly thin concrete just below the slab. The soil was really bad - in fact in some areas it was less dense than water. When shooting some elevations down the length, a truck would drive by outside on the street and the level would shake like crazy from the vibrations.
We ended up drilling through the footings and installing (4) auger cast piling with mushroomed heads just below the footing to engage and support the existing.
The craneways were way out of alignment - roller coaster to the extreme. We had to shim and reset a lot of the rails as well as replace a lot of the crane beams as well since we were going from a 10 ton capacity to a 20 ton capacity.
RE: Evaluating Existing Spread Footings
http://www.ce-ref.com/terzaghi.htm
RE: Evaluating Existing Spread Footings