Hopper tank support plaftorm 2

[Buleeek]

Hello everyone,

I am currently designing a platform to support a hopper tank (tank design by others). It will be a steel frame platform with 2+3 legs (see attached). Of course a truck needs to drive through so I am having an issue with bracing in one direction.

1. What loads would you consider to get the reactions from each tank leg?
2. Where do you think applying a moment connection would be beneficial for lateral stability?
3. Should I design post base/foundation connection as fixed?
4. Do you have any books/articles or advise for a project like this?

Thank you,

 

[ALK2415]

In my opinion,
you should model the whole structure to got the full reactions and forces for each single member
will search for your to give you the steel Silo calculations code
this reference might be helpful "Design of Reinforced Concrete Silo Groups(2019)"
Link
Silos_ Fundamentals of theory, behaviour and design-Spon Press (1998)
Link
Circular storage tanks and silos-CRC Press (2014)
Link
STAAD.Pro software analysis case study [the one you should look into]
Link

 

[human909]

I've designed many of these structures. There are no special tricks here. Just use your normal engineering tools. Pay attention to load paths, vertical and lateral. You current sketch does not seem to have considered basic load path design.

1. All relevant loads, eg dead load, product load, wind load, seismic etc.. This is basic structural engineering.
2. This is really something you need to investigate yourself if you cannot answer this. Choose a suitable lateral load path.
3. Fixed or pinned can both work with suitable designs.


If you ha specific questions related to silo out loading structure design I'd happily help. But these are general questions either from a student or a very inexperienced engineer.

 

[JLNJ]

Looks like you need to hire a structural engineer.

 

[JStephen]

Usually, that whole assembly shown would be designed by one party, not by separate parties.
Sometimes that is the silo designer, sometimes that is a consulting engineer.
Usually, there would be legs supporting the silo in whatever configuration was needed, and that lower platform would then also be supported off those legs.
Not one set of legs up to the platform, then another set of legs, etc.
In designing the silo with the legs attached to it approaches can vary as to whether legs are treated as pinned at the base or fixed at the base or partially fixed, etc., and so the loads applied to the lower structure may vary accordingly.
If there are significant thermal differences involved, it all gets more complicated.

 

[human909]

Usually, that whole assembly shown would be designed by one party, not by separate parties.
Sometimes that is the silo designer, sometimes that is a consulting engineer.

Usually, there would be legs supporting the silo in whatever configuration was needed, and that lower platform would then also be supported off those legs.
Not one set of legs up to the platform, then another set of legs, etc.

Neither of those statements are accurate in my jurisdiction and certainly others I have observed this is often not the case. Of course what is common in one jurisdiction may be completely different in others.

A transfer based design is the most common design in my country. Round silos are a generally commodity item and mass produced. The are cheap items that a uniformly round with uniformly distributed axial loads and require numerous columns and legs to support the UDL at the ring of the silo. If an off the shelf silo is being used on an elevated platform transfer beams are certainly common. If the elevated platform has drive through requirements then that requires significant gap in the otherwise closely spaced silo legs.

(I've designed many of these structures often with 10-20 silos in total.)

 

[Buleeek]

If you ha specific questions related to silo out loading structure design I'd happily help. But these are general questions either from a student or a very inexperienced engineer.

human909, I have done many steel structures, this one is my first steel platform for a storage tank, hence my questions. I just finished creating a model and performed an analysis, but still have some questions. You clearly have a lot of experience in this subject and I was wondering if there is a way to discuss this particular project with you privately (no need to clutter the forum)? I created an email for this purpose: storagetankplatform(AT)GMAIL.COM

Thanks,

 

[human909]

Hi Buleek. If you want to discuss then this is the appropriate place, sorry I won't discuss directly on email.

Judging by your comments you seem to be adept at modelling steel structures presumably in a structural analysis software package. However if you are unsure about how or where to use moment connections it would seem that you need to better understand load paths and moment frames.

There are numerous example of such structures here. LINK (Note there likely is more than one example there that would not be structurally adequate at ultimate loads. Agricultural equipment is sometimes built without proper analysis, I've seen some bad examples in my locality too.)

If you have specific questions then please ask. In my experience wind and seismic forces can be quite significant so don't underestimate the lateral stability requirements. Though I suspect you have already discovered such challenges through your modelling analysis.

 

[EireChch]

Buleek - the idea of these forums is for open discussion. Ask the questions here so others can learn. I follow structural forums too and still need the very basic stuff explained to me. I am sure others are the same.

 

[dhengr]

Buleeek:
If the sketch you provided is fairly accurate, you might try a 16 sided ring beam sitting on top of your support structure horiz. beams. This ring beam incorporates the 16 legs, which come with the tank, as vert. members btwn. inner and outer light stl. web pls. This makes up a box beam with width determined by the tank legs, and a height to be determined. It has a fairly husky continuous bot. flg. pl., a top flg. pl. btwn. adjacent legs, and can have diag. web members similar in size (box beam width) to the tank legs. The diag. web members potentially can transfer load away from some tank legs (every other tank leg?) which are difficult to provide a support beam for in the top of your support structure. This box beam potentially has significant bending (spanning) and torsional strength, and provides good lateral continuity at the top of your structure. This approach probably requires some cooperation from the tank supplier and some considerable attention to good clean engineering design and detailing, but has the potential of cleaning up the structuring and detailing of your support structure.

 

[Buleeek]

dhengr,

Sounds interesting, but I am afraid there is no cooperation with the manufacturer.

human909,

Can you help me understand seismic analysis on the tank? With wind loads, I accumulated the pressure in COG of the tank and applied to the structure in 3 different directions (0, 45, 90 deg). Can I go in similar fashion with seismic ? Any info/articles/books about the seismic analysis for this particular structure would be helpful.

Thank you,

 

[human909]

Hi Buleek.

The general approach that I've done and that I've seen done is to have a two moment frames in the direction perpendicular to the truck path and a braced frame in the direction plane that is parallel to the truck path. Sometimes this is done with moment connections to columns other times it is done with a truss. Normally 4 columns per silo is enough. Though expect large columns and large beams.

Your current design has a beam running right underneath the silo outlet which doesn't seem functional. Unless it results in excessive deep beams I'd try to stick to a 4 column approach. Rotate the silo by 11.25 degrees and you will get much better alignment of the silo legs with the beams. You should be able to support the silo with 8 beams (2 silo legs per beam).

Seismic design will obviously depend on your local code. There isn't anything too difficult about it except I would advise to use the full product load as the seismic weight. I am not aware of any articles or books on this subject.

 

[JLNJ]

You write that you have designed “many structures”, yet your questions reveal you know little about structural engineering principles. You are not qualified to perform this design.

Why not leave the structural work to real structural engineers so that the Owner has a proper, safe installation?

 

[Buleeek]

human909, thank you, I agree with you on the beam in the middle, but this is what I was told to do and have to stick to it.

Could you show a sample of wind and seismic load calcs on the hopper tank?

Thanks again for your input I really appreciate it.

 

[Buleeek]

human909,

I was wondering if you (and other forum members) could take a look at the attached pdf with seismic analysis and maybe give your opinion if the obtained values are in range what you normally get on your structures.

Basic information:

24' dia tank on a steel platform.
Platform elevation: +- 16'
Tank height 72'
Assumed building height = 88'

Effective mass weight includes:
a. dead weight of tank (33 kip)
b. self weight of platform
c. soybean load (live) = 1410 kip


Any input would be appreciated.
Thank you