Braces buried in bulk storage bins
Braces buried in bulk storage bins
(OP)
On a bulk storage fertilizer containment building with 16' tall concrete walls I'd like to brace the tops of the concrete walls to not have to design pure cantilevered walls. The material will actually be stored HIGHER than the walls so a brace at 16' would be embedded in the stored material. My concern is not the corrosion aspects of what fertilizer against this brace would be (though that's an issue) but rather the "fluid" pressures that would act on this brace as it is an obstruction to free-flowing material as the piles are created and/or removed from the bin. Anybody have experience with this? Round tubes better than square shapes? Can I look at the forces on these braces as a uniform load equal to the height and density of material above it? Any other suggestions or concerns?
Thanks.
Thanks.






RE: Braces buried in bulk storage bins
RE: Braces buried in bulk storage bins
RE: Braces buried in bulk storage bins
RE: Braces buried in bulk storage bins
RE: Braces buried in bulk storage bins
I could see an argument for designing the brace for almost no out-of-plane loading as well. So this likely would be a judgement call.
RE: Braces buried in bulk storage bins
Angle of repose is around 30 degrees for the material I'm using so I can figure that active pressure Ka.
The reason I'm concerned is that the owner of the firm I worked for years ago had used cables on a really large grain storage facility thinking that the grain would just "flow" around the cables as the "bin" was filled up and he found out that it didn't. Tore that building apart............and I'd like to not repeat the same mistakes that he did. Owner has been out of the engineering world for a long time now and I'm not sure he can answer this sort of question.
In the forum's professional opinion, does a smaller diameter rod that will not have any strength to resist lateral load (but allow for better flowage) be better or worse than a tube perhaps that could be designed to handle the lateral loads (but has a larger tributary area?)
RE: Braces buried in bulk storage bins
Only thing about that scenario that worries me is the P-Delta effect. If it's flexible enough to be easily bent....and it still has to handle axial load.....that could become an issue.
To me, a decent sized HSS is probably the answer.
RE: Braces buried in bulk storage bins
RE: Braces buried in bulk storage bins
I don't know that I'd count on that scenario. I've done storage bins (adjacent to each other) and when you look at them in practice.....you see all sorts of scenarios that could hit you here. I could see the brace being loaded vertically/laterally in spots....yet not putting much pressure on the adjacent wall. (I.e. a pile/pyramid shape on top of the brace (or part of it).) And then (maybe) on the other side of that wall....it gets full active pressure.
Ergo you wind up with your brace being vertically/laterally loaded and getting compression. I'd just design for the worst possible case.
RE: Braces buried in bulk storage bins
at rest...vert and lateral load on brace combined with axial load in brace...
dynamic....dynamic impact load during flow...any chance of vibration?...fatigue issues?..
erosion of brace wall...depending on the type of fertilizer material...
corrosion as mentioned...
round pipe should offer less obstruction than square....
a sketch would help...
RE: Braces buried in bulk storage bins
In such cases, you will wind up with the brace in the left bay going into compression whether you want it to or not. And then with that pile on it.....you've got some moment to consider as well.
Probably the best way is to do it like "Scenario 2". And note no material under that brace in "Scenario 2". (Which is how I should have drawn it in "Scenario 1".)
Not sure how you were envisioning doing the braces.....but this is the first thing that came to mind.
RE: Braces buried in bulk storage bins
RE: Braces buried in bulk storage bins
Thanks.
RE: Braces buried in bulk storage bins
Outside of some thermal contraction or lateral event....I see what you are saying about it (i.e. the brace on the left hand side) never being in compression and having lateral load on it simultaneously. But I wouldn't do it that way .
RE: Braces buried in bulk storage bins
I believe, and I stand to be corrected, that regardless of the multiple combinations of filled bins that are possible on this 5-bin project, it doesn't matter which is filled or empty. If they're filled, the forces are equal and opposite and will counteract each other. In other words, regardless of how the bins are filled, the net lateral forces on the entire structure are zero from a bulk fertilizer standpoint. If every other bin was filled, the two intermediate ones could experience some compression in their braces equivalent to the amount of strain in the tensioned braces. But at that point, there is no fertilizer to load that brace out of plane.
Am I making sense WARose? I appreciate your dialogue.
RE: Braces buried in bulk storage bins
Furthermore, what would you really be getting by doing this (even if it did work)? You'd cut down on some of the reinforcing steel at the bottom of the wall.....but the shears would still put you into having just about the same wall thickness.....and you are likely driving up the necessary horizontal steel.
Me personally, I'd just do it without the braces.
RE: Braces buried in bulk storage bins
One thing I tried was to load 3 of the interior walls on one side and in only one direction (with the other walls unloaded). And what happened was the braces in several bays went into compression as the wall shared the load based on flexural stiffness. I didn't bother modeling the side walls because the results will probably be the same. (Especially for the middle brace.)
So in conclusion: I'd just forget about a tension only brace.
RE: Braces buried in bulk storage bins
Thanks for challenging my assumptions. With an angle of repose 28-33 degrees, it IS possible to fill an 18' wide bin with some one-sided loading. The bins are loaded out from the ends so a really lop-sided pile configuration could only occur during the loading of the bin. I'll have to check on how that is done.
Worst case you could have about 10' higher on one wall than the other given an 18' bin width. That amounts to around a 3,200plf load differential in one direction..............so..........if even one bin was loaded as such, the adjacent brace would go into compression.
I'm thankful you've taken this thread in a different direction as you're exposing to me a load case that I hadn't considered.
I appreciate your help.
RE: Braces buried in bulk storage bins
Anytime.
RE: Braces buried in bulk storage bins
You don't want the braces to be eroded away any time within the next 100 years.
RE: Braces buried in bulk storage bins
With the possibility of unbalanced lateral pressure on the walls, you will need some kind of structure to resist the axial brace forces. The high walls cannot reasonably be expected to do the job by themselves. The attached sketch illustrates a plan view of the building with a suggestion for truss members in the end bins.
BA
RE: Braces buried in bulk storage bins