Effects of Sloshing on Foundations

[CardsFan1]

I have a flat bottom tank and I am designing the foundation.
I seem to recall in the past being told that the maximum seismic foundation load on the tank comes from the tank being full, and therefore no sloshing analysis needs to be considered.
I am searching the ASCE-7 for guidance and I don't see anything quite so explicit.
I don't believe I have enough information to determine Ti and Tc.
Im looking for the EASY OUT. Can anyone point me to a document that confirms my earlier assertion that I don't need to consider sloshing for the foundation design?

 

[ATSE]

Early assumption is incorrect. Even if you have a solid and not a fluid, the early assumption could not be correct. Replace the word "sloshing" with inertia.

 

[MIStructE_IRE]

It changes the centre of gravity and also introduces a horizontal load. Why would you not have to consider this?

 

[CardsFan1]

OK, You have convinced me I need to consider it. Where does ASCE -7 tell me how to do it?

 

[CardsFan1]

ASCE-7 15.7.6 Ground Supported Storage Tanks for Liquids
Ground supported, flat bottom tanks storing liquids shall be designed to resist the seismic forces calculated using one of the following:
a. The base shear and overturning moment are calculated as if the tank and the entire contents are a rigid mass system per section 15.4.2
b. Tanks and vessels storing liquids in Risk Category IV or with a diameter greater than 20 ft shall be designed to consider the hydrodynamic pressures of the liquid...…

This seems to say that if it is not RC IV and less than 20' dia, I don't need to consider sloshing.

I'll keep reading.

 

[JStephen]

In the API-650 and AWWA D100 codes, you calculate the moment acting on the shell due to impulsive and convective (sloshing) action, and also a separate higher moment if the variation of pressures on the bottom is considered. I would assume that the bolted and concrete tank specs have similar provisions.
The codes don't specify the distribution of those forces (should be available if you really need it via the reference documents used to generate the standards).
For ringwall foundations (and for anchor bolts and for shell compression), you just consider the shell moment, for slab-type foundations, the moment from both.
The "sloshing analysis" is just additional moment calculated due to sloshing, it's not especially complicated.
Typically, in low-seismic areas, I'll figure liquid to the top of the shell for forces, figure estimated sloshing wave height via the standards, and determine maximum operating level from that. But don't generally go back and recalculate the moments for that lower level.
For higher seismic loading, you'd want to do the checks at the maximum operating level, which may be below the overflow level.
You may not need Ti at all, and there are approximate (and quick) ways to check that- in API-650, for one.
Tc is based on tank depth and diameter only, and should be easy to calculate.

 

[ATSE]

I assume "flat bottom tank" is steel. If steel, then D100 and API 650 are your codes. ASCE 7 points you back to these codes. ASCE 7 makes it confusing, in that it also repeats a lot of the specific design checks. [aside: ASCE does this with other codes as well.]

However, if concrete, are you familiar with ACI 350-06?
What you are describing is defined using "IBP" (and not "EBP") for the moment equations (and resulting base pressures).
If Including Base Pressure is new to you, it is certainly not the EASY OUT you had hoped for.

 

[HTURKAK]

CardsFan1 (Structural)(OP);



-Apparently you design the foundation only..So , someone will design the tank and should provide you the loads necessary to the design the tank foundation..
-The foundation will experience the maximum effect with the combination of the tank is full + OT moment due to seismic+ vertical seismic loading. The sloshing analysis performed to see the required free board ht etc... Sometimes the word sloshing period is used for convective period.. If this is the case , you are expected to calculate convective and impulsive loading and combine . For small tanks, you may calculate the base shear and overturning moment are calculated if the tank and the entire contents are assumed as a rigid mass system per Section 15.4.2 that is , if the tank is small and have a fundamental period, T, less than 0.06 s.



If you have the dimensions of the tank , content properties , the calculation of Ti and Tc are pretty straightforward..

You did not define the content ..Better to look API 650 APP. E as MR .JSTEPHEN proposed also..