Silo hydrostatic pressure

[Tihomir.Karaba]

Hello,

I'm currently analysing silo for storing corn. The silo is made of S235 steel plates 3mm thick with reinforcing ribs 6mm thick, overall dimensions are 2300x2300x8700. On the attached picture you can find more model information. As you can see side plates are deformed about 200mm, that is quite a lot but having in mind that silo volume is big and steel plates are relatively thin, maybe that's ok . Just for check, we have made the identical model in Ansys and get the identical load distribution but deformation was about 57mm. Could you please clarify following:

1. Is hydrostatic load applied correctly?

2. What 7.85 in the load label [p hyd = (0.0, 7.85)] stands for?

3. Is it possible to display hydrostatic pressure values on the bottom of the silo or some specific elevation?

Thank you very much in advance.

Best regards
Tihomir

[dimogrec · Accepted solution]

2. Kg to KN, 1kg=0.00981KN => 800kg=7.848KN

3. (if I understood what you mean) In the bottom you should have a surface (uniform planar) load. In your case h x Weight= 8.7m x 7.85KN/m3 =68.3KN/m2. You should apply (manualy) this load on the bottom plate.

[Tihomir.Karaba]

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@dimogrec wrote:

2. Kg to KN, 1kg=0.00981KN => 800kg=7.848KN

I understand, thanks

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@dimogrec wrote:

3. (if I understood what you mean) In the bottom you should have a surface (uniform planar) load. In your case h x Weight= 8.7m x 7.85KN/m3 =68.3KN/m2. You should apply (manualy) this load on the bottom plate.

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The silo have hopper at the bottom, and there is hydrostatic load applied also.

I meant, is there any way to display value of the hydrostatic pressure, let say on the elevation of 5000 mm from the top end of the silo,... please see attached picture.

Thanks

Tihomir

[dimogrec]

No, as far as I know there is no way to displaye hydrostatic pressure in a specific level-point.

[Rafacascudo]

You can always divide the load in 2 or more parts , top to EL. 5000mm and another loading from EL. 5000mm to botton. Maybe using load 3p will be easier.

[Tihomir.Karaba]

OK, that's clear also, thanks both very much.

Still, I will attach my model, so if anyone can take a look on it regarding that big deformation, I would appreciate that. Maybe I'm making a mistake somewhere.

Thanks

Tihomir

[dimogrec · Accepted solution]

After a quick look at your model I did not see something wrong except

- warning message "Incoherent mesh on edges". In this case it is suggested (see message 2 from tony and message 3 from Rafal ->  http://forums.autodesk.com/t5/Robot-Structural-Analysis/Structure-verification/m-p/3334637 ) to change setting in job preference (uncklick "Kinematic constrains" and click "Iterative adjustment", also set "meshing options" as displayed in the picutre of the link (keeping or changing element size of FEM is your decision)

[Anonymous]

Dear Tihomir Karaba,

Could you pls explain to me step by step how you assigned the hydrostatic loads to the silo and the hopper at the bottom? After defining the loads, do you have to select the entire structure and apply the loads to it? Just explain to me step by step what you did in creating your model loads. I am investigating a suspended cylindrical silo failure which I have already modeled in Robot, but I am now stuck in the sequence of steps to follow to add loads to the structure.

Other folks are also kindly asked to address my question. It appears straight forward, but I have not handled this type of structure before in Robot.

Regards

[Tihomir.Karaba]

Hello,

I assume that you have already calculated loads to be applied to silo walls, so I would not get into that here.

In my case silo was designed from segments, so I calculated loads accordingly.
In other words, every segment has its own hydrostatic pressure.
Loads are applied using planar load 3p. In the attached picture, you can see sequence to do that.
I have used local system, so you can see that only Z pressure fields are filled in because local coordinate Z of the plates is perpendicular to plate and
directed outside, so the values are positive.

When you fill in values for pressure than you need to designate where each of those pressures is located. I have done it in a way presented on the picture, but you can do it differently. For example, fill P1  & P2 with a same pressure value and P3 with other pressure value that you had calculated for those elevations and accordingly select the points A, B & C. It is up to you.

The same process was applied for hopper loads too.

I hope that this was helpful.

Kind regards,

Tihomir

[Anonymous]

Dear Tihomir,

Thanks very much for the quick response. I thought the application of loads to silos was straight forward! Now I know better! Now please be patient with me, because I am new to designing silos in Robot.

1. Did you model your silo in segments from the cylindrical part to the hopper part? If so, what was the height of these segments (Is it the vertical distance between the joints of the units that form the silo?).

2. Why did you use 3-point planar loading instead of the direct hydrostatic pressure loading? Kindly advise me why? I know there is literature on 3-point planar loading, but kindly explain the concept to me since you have applied it.

3. In applying the loads on the segments of the silo structure, did you consider a unit width of the segments when calculating the loads? What formula did you use to calculate these loads?

4. Did you generate your computational mesh manually or automatically?

5. Now this is the part I am struggling with. After you have generated your segments, are you going to select them one by one and apply the loads accordingly?

6. Is it possible to send me a screencast or screen capture on how you generated your model. I know I am asking a lot, but if you are not able to send me this video of how you modelled your silo, would you please send me a link or forward my request to other members.

Thanks a lot Tihomir. I was always thinking that you can design the cylindrical part of the silo as a continuum and the hopper part as a continuum also.

Hoping to hear from you soon 

Ishmael