ground supported storage tanks for liquids

[braves25]

Hello all....I have a water storage tank that I am only providing the foundation design for. 32' tall x 10.5' dia. Looking at 15.7.6.1 of the ASCE 05, I can calculate the base shear V by using method (a), 15.4.2, where V = 0.3SdsWI. If I use this equation to calculate my shear, do I need to add the Vi and Vc for impulsive and convective (sloshing) components? If so, do I all this to my V from 15.4.2? And, how to calculate Wi and Wc?

Once I get my base shear, would I apply this at the center of mass to calculate my overturning moment?

Thanks!

 

[JedClampett]

This is an extremely complex analysis with all kind of hyperbolic functions and stuff like that. You need to get a copy of ACI 350.3-06 and follow it. It has a lot of formulae, but a lot of them don't apply to round tanks (but a lot of them do). It's based on some work from the 60's from Housner and other references from Haroun.
Don't be surprised if your base shear changes from the ASCE method.

 

[theonlynamenottaken]

Who is designing the tank itself? They would typically be responsible for running those analyses and providing the calculated reactions. Don't reinvent the wheel. At that height/diameter ratio the tank almost certainly needs to be anchored... has the tank designer provided the anchor bolt diameter, tensions, and spacing?

AWWA is the typical go-to standard for steel tanks for water storage. They give very specific guidance on calculating lateral atmospheric loads and anchoring. However, if you aren't the tank designer you'll probably end up guessing on some of the variables you'll need to calculate all of that.

 

[braves25]

The tank and anchorage (if applicable) is designed by others. We have only been hired to provide the foundation design.

 

[structSU10]

In the tanks like that I have done in the past we received reactions from the tank guy for the foundation. Usually they can provide a preliminary tank pretty easily to get started with.

 

[fegenbush]

theonlynamenottaken is correct. Your tank will require anchorage. The foundation loads should be provided by the tank designer. The references common to this application are AWWA D100 or API 650. Both standards calculate the wind and seismic effects similarly.

 

[theonlynamenottaken]

So are you checking their provided reactions? Or have you not been provided the reactions by others? If you haven't been provided the reactions and you are trying to design a foundation for an "unknown" tank, was this portion of the engineering covered in your contract scope? If not then I would typically send a change/add'l service request to the owner stating that you need to perform calculations to determine approximate tank reactions with an associated fee. Historically I've then found that tank manufacturer provided reactions will magically appear.

If not and the owner approves the change then using AWWA D100 calculate reactions keeping track of your assumptions (such as TCL = top capacity level, MOL = max operating level, shell thickness, roof weight, floor thickness) and add ~15% to account for inaccuracies in your assumptions. Then provide all of these calculated reactions and assumptions on your drawing cover page.

Technically, to calculate seismic shear and overturning moment per AWWA D100:
V = sqrt{ [Ai x (Ws + Wr + Wf + Wi)]^2 + [Ac x Wc]^2 }

where A = design accelerations, W = weights, i = impulsive, c = convective, and s,r,f = shell, roof, and floor

The moment calculation adds in Xs, Hr, Ximf, and Xcmf for the respective heights of force centroids for each of the above components, minus the floor which shouldn't add any moment (at least at the top face of your foundation). Calculating Wi, Wc, Ximf and Xcmf is a bit daunting, with hyperbolic trig functions as JedClampett described.