nicoga3000
Civil/Environmental
I recently came across a report that gave loadings, foundation properties, allowable bearing, and actual bearing for a large water tank. Something comes across as very odd in this design.
Loads
D = 2860 kip
F = 8360 kip
W = 7800 kip*ft
Foundation Dimensions
OR pad = 25'-10"
IR pad = 10'-1"
CL ringwall = 19.125'
A = 1777.2 ft^2
I = 341672.7 ft^4
Qa = 6000 psf (no increase for wind allowed)
The information above is given to help determine the bearing due to the wind loading case (which is called out as D + F + W in the report). Given the information I have, this is what I discovered...
D + F + W
(D + F)/A + Wy/I
(2860 + 8360)/1777.2 + 7800*25.833/341672.7
11220/1777.2 + 201497.4/341672.7
6313.3 psf + 589.7 psf
6903 psf > 6000 psf (FAIL)
They list this combination as having a resultant of 5910 psf. They also make mention of using the Meyerhof method for effective area.
OK, so my approach for their moment due to wind may be off (given that I'm using a simplified My/I approach), but their static loads give a bearing pressure higher than allowed in the geotechnical report. Odd.
Can anyone give any insight on how this is possible? Am I missing something? Is there a fundamental approach to bearing capacity that I'm missing? Your loads are what they are - I don't imagine you can just magically reduce them (and in my line of work, we definitely can't, ha). If I were to design this foundation, it would have been slightly larger given the static capacity of the soil.
Any thoughts and insight on this would be fantastic!
Loads
D = 2860 kip
F = 8360 kip
W = 7800 kip*ft
Foundation Dimensions
OR pad = 25'-10"
IR pad = 10'-1"
CL ringwall = 19.125'
A = 1777.2 ft^2
I = 341672.7 ft^4
Qa = 6000 psf (no increase for wind allowed)
The information above is given to help determine the bearing due to the wind loading case (which is called out as D + F + W in the report). Given the information I have, this is what I discovered...
D + F + W
(D + F)/A + Wy/I
(2860 + 8360)/1777.2 + 7800*25.833/341672.7
11220/1777.2 + 201497.4/341672.7
6313.3 psf + 589.7 psf
6903 psf > 6000 psf (FAIL)
They list this combination as having a resultant of 5910 psf. They also make mention of using the Meyerhof method for effective area.
OK, so my approach for their moment due to wind may be off (given that I'm using a simplified My/I approach), but their static loads give a bearing pressure higher than allowed in the geotechnical report. Odd.
Can anyone give any insight on how this is possible? Am I missing something? Is there a fundamental approach to bearing capacity that I'm missing? Your loads are what they are - I don't imagine you can just magically reduce them (and in my line of work, we definitely can't, ha). If I were to design this foundation, it would have been slightly larger given the static capacity of the soil.
Any thoughts and insight on this would be fantastic!
