Lateral Earth Pressure in Ringwall foundation - Active/Passive or At-Rest
Lateral Earth Pressure in Ringwall foundation - Active/Passive or At-Rest
(OP)
I am designing the ringwall foundation for a 150,000 BBL API 650 Tank. While calculating the hoop stresses, what value of earth pressure should be used (At rest/Active/Passive)?
One view is that the ringwall will not move much and at-rest pressures should be used.
A design spec of a company (won't name them) specified to use active earth pressure.
Third theory is that the ringwall is rotating a bit, so there should be passive pressures in the top half while active earth pressures in the bottom.
If anyone has any insight or references on this, it would be really helpful.
Thanks
KapoA





RE: Lateral Earth Pressure in Ringwall foundation - Active/Passive or At-Rest
When you can't answer that clearly, you assume the worst. No outside fill, at least in some places. Why stick you neck out?.
RE: Lateral Earth Pressure in Ringwall foundation - Active/Passive or At-Rest
Outside fill is neglected.
RE: Lateral Earth Pressure in Ringwall foundation - Active/Passive or At-Rest
Before you doing anything creative, make sure the code likes the artwork you are trying to wow the world with.
RE: Lateral Earth Pressure in Ringwall foundation - Active/Passive or At-Rest
any references (API 650 section no's) to back your thought?
RE: Lateral Earth Pressure in Ringwall foundation - Active/Passive or At-Rest
Unless I am not understanding your specific loading, there are only two options. The wall isn't moving into the soil mass, right? My question is: is it worth the time to investigate whether the wall will move enough to develop active pressures? Also, if the soil being contained is very granular and self-consolidating, it will have a very hard time developing active pressures.
Maybe if there is an additional moment at the top of the wall (inducing a large and predicable movement), a soil with good arching action, and the right aspect ratio and wall thickness it will happen. Again, is it worth the research? If the research leads you to "I am not sure", was it still worth the effort?
Before you doing anything creative, make sure the code likes the artwork you are trying to wow the world with.
RE: Lateral Earth Pressure in Ringwall foundation - Active/Passive or At-Rest
neutral axis being the central axis of the cross section in the plane of the ring. ROARKS FORMULA FOR STRESS AND STRAIN SECTION 10.9
Also Refer PIP STE 03020 Page 18 section 4.6.5.6 for reference
Now the displacement for cantilevered wall you have mentioned is 0.001H. So the angle of rotation will be 0.001 rad or 0.057 degrees.
Rotation angle for a ringwall (behaving as a narrow ring ) is MR^2/EI where M is twist moment, R is tank radius.
Say my ringwall is 2 feet by 5 feet. Assume Tank radius of 70 feet. Twist moment Mt approx 700 kips. E say 29000 ksi.
Angle of rotation comes out to be 0.039 radians (2.25 deg) > than 0.001 to mobilize active and passive.
So based on this, the upper half of the ringwall is moving into the soil while the bottom half is moving out. The lateral earth pressure coefficient for passive will be much higher and will really bump up my hoop stress values. for clay Ko is about 0.7 but Kp is about 1.82. while Ka is about 0.55.
I should take an average of Ka and Kp to calculate hoop stress acroos the wall height but even that average value is much higher than Ko. Average value is 1.18 and Ko is 0.7. My area of steel calculated is about 70% more!!
RE: Lateral Earth Pressure in Ringwall foundation - Active/Passive or At-Rest
RE: Lateral Earth Pressure in Ringwall foundation - Active/Passive or At-Rest
Before you doing anything creative, make sure the code likes the artwork you are trying to wow the world with.
RE: Lateral Earth Pressure in Ringwall foundation - Active/Passive or At-Rest
Thanks.
RE: Lateral Earth Pressure in Ringwall foundation - Active/Passive or At-Rest
RE: Lateral Earth Pressure in Ringwall foundation - Active/Passive or At-Rest
Before you doing anything creative, make sure the code likes the artwork you are trying to wow the world with.
RE: Lateral Earth Pressure in Ringwall foundation - Active/Passive or At-Rest
I agree that tensile strain is most likely negligible and that should not cause mobilization of earth pressure.
@ a7x1984 - this approach is actually giving more rebar than the at-rest case; so i was concerned that the at-rest case may give less rebar than needed. Since there is a FOS of 1.6 it might absorb that difference.
All - thanks for your inputs and valueable feedback so far.
RE: Lateral Earth Pressure in Ringwall foundation - Active/Passive or At-Rest
In Russia building design you!