Grain Pressure Equivalent Fluid Density

[EngSD]

I am looking for some other opinions/information on how grain pressure along a perimeter wall, such as a flat storage building, should be calculated. In the past I have used Rankine's equation for active earth pressure with a backslope in determining the equivalent fluid density. If I were to assume angle of repose of 25 degrees, angle of internal friction of 25 degrees, and a unit weight of 52 pcf the equivalent fluid density calculates out at 42.4 pcf. However I have come across an article that states that the equivalent fluid density for peaked corn is 23 pcf (see pg 2 of link below for article).

Does anyone know how the author came up with this value? Any help would be greatly appreciated.

P.S. The author doesn't reference where his values were obtained and I emailed him asking and did not receive a response.

http://www.ag.ndsu.edu/graindrying/publications/ae-84-temporary-grain-storage

Thank you.

 

[CELinOttawa]

You're looking for bulk storage. This is a pretty specialised area of practice, and honestly requires a great deal of time and effort... There is a text by

 

[paddingtongreen]

I used to use Janssen's formula. I don't knowm if you can adapt it for your problem.

Start research with this PDF.

Michael.
"Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved." ~ Tim Minchin

 

[JedClampett]

We have a book by Gaylord and Gaylord that's titled, "Design of Steel Bins for Storage of Bulk Solids"
Luckily, I've never had to use it.

 

[JStephen]

"Although the formulas in Table 1 can be used for shallow bins, Rankine's active pressure...is sometimes used for bunkers. In this case, q=gamma*Y and p =kq." This is a line from Gaylord & Gaylord's Structural Engineering handbook. In a table in that section, they show for corn gamma-min = 46 lb/cuft and kf = 0.53, which would put you pretty close to your 23 pcf value.

I'm not saying this is right and the way to do it, just pointing out a possible source.

One issue with Gaylord & Gaylord's bin book is they'll give you three different ways to figure the pressure and you get three completely different answers when you do, which tends to turn it from science to voodoo.

 

[EngSD]

I'm going to check the office library to see if we have that Gaylord & Gaylord Structural Engineering Handbook. I know we have the "Design of steel bins for storage of bulk solids" by the same authors.

JStephen in case I can't find the book does it mention whether the values they are providing take into account backslope?

Thanks.

 

[JStephen]

It doesn't specifically say. In their general definition of Y (for all methods, not just this one), they show that if the fill is sloped, Y is to the centroid of the sloped part.
This is on the bottom of Page 22-4 in the Second Edition, if that helps.

 

[CELinOttawa]

Darn it, I don't know what happened but I was trying to point you towards the Gaylord & Gaylord text...

My old office had two versions. The older edition had much simpler methods, but something tells me you might be found to be practising behind the state of the profession if you don't use the new methods.

 

[paddingtongreen]

This is an old book, out of copyright, but it was the Bible for a long time, The Design of Walls, Bins and Grain Elevators

Michael.
"Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved." ~ Tim Minchin

 

[Splitrings]

ASABE EP545, Loads Exerted by Free Flowing Grain on Shallow Storage Structures

 

[EngSD]

For those interested the I bought the ASABE EP 545 document and it covered exactly what I was looking for. Calculates the pressures using a modified Coulomb's equation and a equivalent grain height.

It provides a values that are slightly less than the Rankine equation I was previously using.

Might be in line with the Gaylord and Gaylord book which used the centroid of the sloped height for the equivalent grain height but I didn't have that resource.