Tank Wall Analysis

[KHoff]

I am working on analyzing the framing for the wall of a tank that holds 300 tons of roof granule. I am struggling with determining the load to apply to represent the granule when the tank is full. Does anyone have a recommendation for an equivalent fluid pressure that could be used? I have seen an EFP around 25 psf/ft used for gravel backfill, but the granule is loose and much smaller. I appreciate any suggestions.

 

[SlideRuleEra]

Equivalent Fluid Pressure of a granular substance depend on two variable; the unit weight (pcf) and the angle of repose (deg.).

Unless you have more appropriate info, I found this data: Roofing Granules Physical Properties
The "bulk density" is given as 90 to 96 pcf.

Published angle of repose for "dry gravel" is about 37^o.
For "clean, dry sand", about 34^o.

Suggest staying conservative and calculating EFP using 96 pcf and 34^o.
Note: Looking at a table of angle or repose for various granular materials, 34^o is the lowest (most conservative) value I saw.

EFP = 96 pcf x tan² (45^o - 1/2 x 34^o) = 27.1 pcf
Say, 28pcf

Not much different than the value you found, but at least 28 pcf is based (partially) on the properties for roofing granules.

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[JStephen]

A couple of years ago, I went through a short course on flow of solids in bins and hoppers. One lesson from that is that if you actually want numbers that have much meaning, you have to test your actual product being stored, as opposed to fetching up a handbook value for the properties.

If the structure is small enough, treating the product as liquid (using the actual density) for the outward pressure and treating it as plugged (product entirely supported by the shell) for vertical shear loads will simplify the design considerably.

 

[JAE]

There's a whole section on this in Gaylord & Gaylord's Book - not sure if you have access to it.

https://www.amazon.com/Structural-Engineering-Handbook-Edwin-Gaylord/dp/0070237247

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