tank anchor with shear blocks

[Eman1]

Hello,

I am looking for standard design info for open top storage tanks secured with shear blocks to resist spinning due to internal agitator baffle loading.

Any general information regarding the design, restriction or design parameters would be very helpful.


The reference thread thread809-161418 mentions that dig1's has done this before, maybe he could share some insight.

Best regards,

Elmar

 

[Duwe6]

I've never seen or heard of anchoring a tank for the torque of a mixer. If you are positive that your walls are insufficient to withstand the starting torque of a mixer, specify that the mixer is to be put on a Variable Speed/Frequency Drive -- VFD -- and 'soft' started.

The static friction of the tank bottom is not going allow the tank to rotate due to a 'hard' start of a mixer.

 

[saplanti]

I guess the shear key solution is adequate for the torsion, however you stlll need to proove that the wal natural frequency is not matching the forcing natural frequency.

To make the roof wall stiffer you may use stiffeners, but to make the shell stiffer you may be forced to use anchors for the boundary conditions.

 

[Eman1]

Hello,

Assume the following scenario. You have a open top tank with a top mounted agitator. The inside of the tank has a number of baffles attached to the tank shell. Now turn the agitator on and create flow against the outside baffles. This will create pressure as the fluid flow is restricted. This pressure times the baffle plate size equate to a force. This times the number of baffles is the circumferential force acting on the tank.
Let's disregard the action - reaction theory for a moment. Now turn of the agitator motor. At this moment you have a force acting on the perimeter of the tank as the liquid's mass continues to push.
That means that there is a possibility of the tank turning. If I have load sensitive nozzles & piping, I need to confirm that no motion can occur.

My question is, how do you secure a open flat bottom open top tank
if you are not allowed to bolt the tank down due to seismic restrictions.
Has anybody done that? Please advise.

Thanks

 

[saplanti]

The concept is the same for the open tank. in case the agitator is top connected to the tank by structural members, the forcing frequency vs natural frequency concept will be the same in addition to other structural/mechanical requirements.

I do not understand why there is a restriction on the anchor bolts due to the seismic effects. This not reasonable. Let us assume you can not use anchor bolts at all for some reason, so you need to make the structure bottom mass sufficient not to go into resonance first, and move under the actions second. You may be using vertical/horizontal stiffeners to increase the natural frequency on the shell/side wall, and adding additional mass close to bottom or at the bottom for other actions to use against rotation or shear.

Or give it to the expert engineer with all available data to design for you. I started having a feeling that you are not aware of many design requirements on the issue.

Regards,

Ibrahim Demir

 

[11echo]

Look at using "anchor chairs" on the tank walls ...I've used them in high seismic zones to keep tanks from tipping over, they'd work at keeping a tank from spinning too.

 

[IFRs]

I think I'd just extend the bottom plate a bit further out on to the foundation and put anchor bolts in radially slotted holes.