Grain Bin Settlement

[caddyr2]

Here's my question: I am working on the settlement of a proposed grain bin which has appx 6' stemwalls, 4' wide footing at base of stemwalls whereas the footing is exposed on the outside of the stemwalls but the inside of the stemwalls is backfilled with granular material to 6" below the top of stemwall to facilitate the 6" bin floor slab and includes a tunnel system below the grain bin floor slab. Based on Janssen's formula it appears that the walls will receive appx 20% of the loading. Where I am stuck at is how does someone easily determine the loading on the 4' wide stemwall footing where it has a lb/ft loading from the friction on the walls as well as some loading due to the granular infill and a portion of the weight of the corn acting on that footing "ledge" as I will call it. Does this make sense to anyone else because the longer I look at it the more it becomes twisted in my mind.

 

[BigH]

Why not sketch it up and post it . . . with details - might help us (and you) visualize it more precisely.

 

[oldestguy]

Your explanation is clear. It is the typical grain bin situation.

You will have a "silo effect" vertical wall load where the grain hangs up on the sides as it is removed. There I have no answer as to the friction value of corn, but you can do some simple direct shear tests of compacted corn to get a feel for this.

The extreme would also be what does it take to crumple those side wall sheets in the form of vertical loading of them.

I'd use plenty of "longitudinal beam reinforcing" in that ring wall, since popping a seam at the bottom will raise hell with what's in the neighborhood.

 

[BigH]

http://www.omafra.gov.on.ca/english/livestock/dairy/facts/88-033.htm

http://www.civil.columbia.edu/em2002/proceedings/papers/271.pdf

- this actually has tests on corn and other mat'ls

http://www.jenike.com/TechPapers/silo-failures.pdf

http://www.international-agrophysics.org/artykuly/international_agrophysics/IntAgr_2002_16_1_23.pdf

 

[aeoliantexan]

I would include the weight of the sand fill and the grain directly above the inside leg of the footing, the wall load you described, and the weight of the footing and stem wall. I suspect that the distribution of grain loads will vary with respect to the tunnel location, but the above is a fair guess for design purposes.

I agree that the ring wall should be well reinforced for beam action. The tunnel penetration is a potential weak point. The 6-foot-deep beam can be very stiff and strong to accommodate tendencies for differential settlement. I once saw such a tank than settled over one foot differentially due to an unknown pit full of trash under one side. The foundation and bin simply tilted with no distress to either. For repair, the bin was jacked up; a wedge-shaped levelling slab was poured on top of the existing floor slab; and the bin was set back into position.

 

[caddyr2]

Thanks BigH. Those articles were very useful. I was just concerned that there are other forces rather than what is described in Janssen's and a couple of the papers looked deeper into the forces.

aeolian: Those are the weights I am looking at, however, the grain weight directly above the inside leg of the footing is a little more difficult to calculate because I have the vertical loading on the bin walls due to the friction of the corn and corrugated steel and so part of the corn above the footing is already calculated into that footing load and if I were to add the appx 60 ft tall column of corn above that footing would be using that weight twice since it is already being supported by the walls. Do you see what I'm trying to get at?

Also I agree about the reinforcement of the ring wall, however, that will be the structural engineers design based on the settlement estimates that I supply to him.
I'll try to attach a rough design of what im talking about to see if it makes more sense like BigH suggested.

 

[oldestguy]

On the wall reinforcing, I think you should advise some guide, such as consider that a 10 foot length of the wall has nothing under it and the wall has to span that as a continuous beam. Otherwise you do not tell him much that he can design for. To be conservative make it 15 feet.

I hope no one forgot about the snow load on the roof.

On the popping of bolts on that bottom series of plates, when the side then opens up like a zipper it sure has a pretty good force against neighboring structures. In the case I once saw, this was due to sitting on compacted fill that replaced a soft layer of cinders. However, the diggers only went to the edge of the wall footing for the undercut edge. Lateral support for the compacted fill gave way and "all hell broke loose" due to major differential settlement.

 

[slipstick50]

Take a look at ASABE publications for information regarding grain properties, bulk densities.

Be careful with Janssen's formula as it is for estimating "deep" storage bin loading vs "shallow" bin loading.... Often when bins are bin diameter with relation to height, the governing soil loading is at the bin center..... hence compacted bulk density x peak height is the floor level loading... say 100' grain peak height in a 105' bin, probably have 52 PCF grain density sx 1000 = 5000 PSF center of floor load.

friction loads on shallow bin walls,, use high coef. of friction, and treat the grain as a semi fluid material.. with l/v of about 0.5 estimate for design lateral pressure/vertical pressure = l/v

in ASABE publications very basic friction design is 0.37 and design bulk density is 52 pcf

could write books on this stuff... lots of variables and judgement calls..

r