elevated swimming pool design considerations 2

[MMOT]

Hope someone can send me in the right direction..
I am working on a hotel design which incorporates and swimming pool on/in the second story, above occupied space. Seems like there should be some code guidance on this for seismic loading and other considerations but I havn't found any yet.

Does any one know of a code or standard directly relating to this situation or any other resources which may provide some guidance?

Thanks,

 

[SlideRuleEra]

My recollection is that the American Petroleum Institute has seismic standards that consider a liquid "sloshing" around in a container (a tank) during and earthquake. I believe the forces can be considerable. Try

http://api-ec.org

 

[thaidavid]

MMOT,

This would essentially be the same as a tuned mass damper (sloshing type), which would actually be a positive factor in resisting seismic shears. You might want to search on this subject to get further input.

David

 

[Lutfi]

I can recall this subject being covered in one of the MIL design handbooks. I am not sure if it is still available on the internet. I think it was chapter 13. I would definitely consider the sloshing effect plus gravity loads which I think is pretty severe considering water weighs 62.4 pounds per cubic foot.

Good luck

 

[LPPE]

I agree with thaidavid about the mass damping effect.

I'm not sure of the lateral design forces, but I have recently inspected framing around an elevated pool in a 10yr old hotel. All i can say is PAY CLOSE ATTENTION TO WATERPROOFING! The chlorinated pool water seems to eat steel for breakfast. Make sure all bolts, connectors, members, etc. are suited for the environment! Or you'll be calling an engineer in 10 years to come figure out whats gonig on.

 

[pcronin]

MMOT:

I am facing a similar condition with a hotel and a pool on the third floor. Have you found any design guides for siesmic loading of an elevated pool?

If not, I will look into the sloshing effects found in the tank design manuals. I do feel that the pool should act somewhat as mass damper, but I don't know how you would quantify it's contribution. Seems like you either go with sloshing and amplify the lateral forces, or go with damping and decrease the forces. I just don't want to be overly conservative.

 

[JStephen]

The tank information tends to be for round tanks. So if your pool isn't round, you'll be hard put to come up with "exact" numbers for it. Locate a current copy of AWWA D100-96 for starters. A lot of the seismic design is based on a TID-7024 document issued long ago, and I believe it does address square tanks (or derives equations for square, then applies them to round). You might try the Steel Plate Fabricators Association for copies of it- look for a "corrected" version.

For "standard" tank design, with a ground-supported tank, the design assumes a certain part of the water volume acts as a rigid body with the tank shell, while a certain portion of the water acts in sloshing. The net effect of considering the sloshing is a reduction in seismic loading for larger tanks (with slow sloshing period).

For elevated tanks (IE, municipal water towers), the sloshing is ignored, and the tank/ tower is treated as a cantilever with lumped mass at the end to find deflection, period, and then seismic force. This is probably partly due to the difficulty of calculating sloshing effects in the different odd-shaped containers in use. This approach might work best with a typical odd-shaped pool as well.

 

[MotorCity]

All,

I disagree with the comparison of a mass damper to that of the sloshing of the pool water during a seismic event. First, mass dampers are solid (usually steel slabs), not liquid. The dynamic effect of solids and liquids is not comparable. Second, most mass dampers are electronically controlled based on the intensity of the movement, they are not free to swing like a pendulum. Just my two cents

 

[miecz]

ACI publishes ACI 350.3-01 "Seismic Design of Liquid-Containing Concrete Structures". We use it for Wastewater Treatment Facilities.

 

[pcronin]

MotorCity

I agree with you that the damping forces can't be used. It would mean that the water would have to slosh at the same frequency as the structure AND in the opposite direction. There is no true way to determine that movement so it can't be assumed to help. Furthermore, if the water sloshes at the same frequency and same direction, you will have resonance and the forces will be amplified.

So now I have ruled out the probability of the pool "helping" in a seismice event. Now I am working on quantifying the magnitude of the force due to sloshing in addition to the weight of the water. I am familiar with the AWWA and I anticipate using it's criteria for my design. We will see how it goes.

 

[mrMikee]

The old UBC codes used to have something about elevated water tanks. One of the factors was 2.5 and included sloshing. At the time I designed bins and got guidance from ICBO to use 2.0 (instead of the 2.5) specifically because the bulk solids in bins wouldn't have the sloshing effect. In my opinion this suggests that the seismic forces are amplified in water tanks rather than having a damping effect.

Sorry that this is so vague but I don't have those codes anymore and don't remeber exactly what the equation was. Just wanted to throw in my 2 cents.

-Mike

 

[MMOT]

What a "blast from the past"
Unfortunately my experience can be of little help. I agree the pool should not be considered a benefit, and I made my initial design along the lines of mrMikee's response with a "dynamic factor" of 2.5. Since mine was only 1 floor above grade, I was able to convince the architects to allow concrete shearwalls to support all 4 sides of the pool deck resulting in a plethora of strength and stiffness concentrated near it (as well as providing something to frame the deep concrete beams that formed the edges of the pool into and solving some other diaphragm issues). The client then had a change of heart and dropped the entire project due to political issues, so we never finished the final design. Good Luck!

 

[mrMikee]

The 2.5 factor accounts for both the water contents and an elevated braced frame, I think. The effect of sloshing therefore would be 1.25 (2.5/2). But this is from an old code and from what I remeber. I would hope that there is some better technical info these days.

-Mike