Reinforcement for tall tanks with high roof load 1

[BigTank]

First time poster, long time lurker.

I would like to amend a closed thread that I was just reading.

thread404-8962

This thread was VERY helpful, but it leaves me with a couple of additional questions.

To recap the problem in the above mentioned thread:

-We have an approx. 12' dia. tank with a 1000# agitator drive to be mounted on top.
-The tank has a flat roof
-How do we stiffen to roof appropriately

I would like to amend this question with a couple of concerns:

-Increase the weight of the agitator to 2000#
-My tank is approx. 45' tall: does this require any concern for lateral forces such as wind, or increase any concern for vibration? Does anyone have any tools (calculations, experience) to comfort me considering the possibility of this tank 'toppleing'?

 

[JoeTank]

A 12 x 45 tank will blow over in high winds if its empty. A tall tank also raises concern with a large roof mechanical load if seismic loads are part of spec. What you are describing is normally anchored and the agitator will be supported on a grillage of 12" beams or channels. Criteria is stiffness, not stress for beam design.

Joe Tank

 

[BigTank]

Your post points me in the right direction, but I'd like to amend my situation again, and ask for more specifics.

This tank is anchored. Seismic loads have been considered, although intuition tells me this increased dead load most likely will require re-examination in this capacity.

As for the support system you describe, could you be more specific, i.e. is the grillage of 12" members mounted to the tank shell or is it supported from the ground? Why 12" beams or channel? That seems pretty heavy if welded to the shell, but possibly reasonable if anchored in earth...

 

[JoeTank]

Lets assume agitaor requires a 36"x36" mounting flange. Rough layout would be two W12 at about 42" c-c running parallel across roof. W12s would be used to form a box at center of tank. Beams would typically project beyond edge of shell and be supported on vertical stiffeners welded to the upper shell course. I'd guess they would run about 3 ft down shell. Roof beams would be above roof plate and be seal welded to lower flanges of W12. Another set of smaller beams would run at 90 degrees to main beams and would be spaced as required to support roof plate.

Joe Tank

 

[BigTank]

Thanks Joe! That's pretty close to what I was thinking. It's actually a pretty small mounting flange: 8" weld neck (read customer afterthought).

Fitter, happier, more productive

 

[plasgears]

Tanks Joe Tank. I would have done the same thing. Had a stint in process vessel design many moons ago.