Pressure for silo with flat bottom and transitional outlet 6

[mte12]

Hi, I've looked at design codes and literature for a while, to quantify pressures at the outlet (see below, green part).
To describe, it's a cylindrical silo with a flat bottom, and rectangular outlet which is as tall as it is long.

Please help as to how to treat this.

 

[HTURKAK]

I will suggest two tier calculation;

- First calculate the base pressure at the bottom of the 10 m circular silo using Janssen or Reimbert method , ( you can find the formulas and some design data at silo design books or moreover soil mech.handbooks e.g. Bowles J.E.-Foundation Analysis and Design)

- Then model the rectangular portion using equivalent diameter having hydraulic radius R= area/perimeter . ( In your case R=8/12 and imaginary diameter
D/4 = 8/12 > D= 2.67 m R= D/4 for circular walls )
- The total ht of the equivalent silo for rectangular portion would be = X+ 4 m and calculate the X value with inverse calculation using the base pressure at the 10 m circular tank .
- Then calculate the outlet pressures using total imaginary ht.

 

[JStephen]

First question is, "Will it flow?" That can get rather involved, and may better be left to specialists. I took a 2-day short course (ASME) on the topic several years ago. One thing I recall is that it's hard to get good answers on that question without actually testing the product (as opposed to using typical values from handbooks, etc.)

Second question: Structural design. One approximation that comes in very useful for "small" silos is to assume entire weight of contents is supported on shell to check compression in the shell, then treat contents as a liquid to check lateral loads and loads on the bottom. For larger silos, this can be overly conservative. I would say from your dimensions above, that your silo is either borderline or above the point where this approach is useful.

In the past, I've used the Gaylord and Gaylord silo book. It refers to Janssen's equation as mentioned above. But on one page, it says "So-and-so recommends these factors" and gives recommended factors. Then a couple of pages over, "But other so-and-so recommends THESE factors" and gives a completely different set. And if you run the loads up both ways, they are considerably different. The moral being, there is a considerable amount of uncertainty as to the actual pressures/forces generated, regardless of the basis used.

Note that where you have a square or rectangular opening like that, the pressures in the shell will not be exactly symmetrical around the shell, so you may require stiffeners on the shell to hold it round.

 

[human909]

Two good responses there. So there isn't much more too add. MTE I'd definitely approach all of this with caution if you are not used to silo design. If you take a leaf out HTURKAK's book and remember the broader approaches of splitting problems up.

First question is, "Will it flow?" That can get rather involved, and may better be left to specialists. I took a 2-day short course (ASME) on the topic several years ago. One thing I recall is that it's hard to get good answers on that question without actually testing the product (as opposed to using typical values from handbooks, etc.)

Well it will definitely be funnel flow if it does flow!

Regarding product testing I tried to go down that path with a company I work for. I spoke with the firm Jenike & Johanson. The costs of testing and analysis were very high which basically rules it out for so many applications. Where it is easier and cheaper to be conservative and rely on "experience". But in the big world of material handle eg mining, they manage to be worth the fees they charge.

 

[mte12]

Thanks HTURKAK, JStephen, human909, comments were all very helpful