Grain slab size

I have a used grain bin I'm getting ready to put up, its probably 18-20 ft tall and 6 across. I watched a video on u-tube of a guy installing one of these, he bolted it to the slab with anchors drilled into the slab.

The bin does not have any plates on the legs, my plan is to weld flat plat steel ( with holes for anchoring ) to the legs and then drill and concrete and anchor.
My question is how big should I make the slab and how thick and any thoughts on using an anchor system that you drill into slab the use bolts or lags?
Thanks

If you are pouring a new slab I would think it would be handiest to
set the anchors before the pour, but I may have misunderstood
what you were describing.
Zach

Use galvanized L brackets. Welded plates will rust and fail.

Make sure your slab is high enough so when you empty the bin the auger hopper slides under the unloading auger. Ours are a few inches to low for the auger we have so we have to dig down. Creates a wet spot.

You could see if the manufacturer has details on installation, ie; slab connection, for dimensions, size etc. steel plate, anchor size and concrete details, thickness, reinforcing etc.

If not, size the steel plate, weld, steel should be protected, meaning rust and mill scale removed, hard to field galvanize, maybe something durable like ship paint or something substantial to stop rust. It may possible you could have legs added to the steel plate, holes drilled in both the plate and legs, as well as the legs to the grain bin to match, most steel or welding shops should be able to send out those pieces for galvanizing, connect the 2 in the field already finished, place on your slab, be prepared to shim, I suppose you could use slots for adjustment, but shims would be better, like setting steel column base plate onto a column footing.

Once you place the bin on the slab, that has been poured in advance, say 28 days before, you can easily drill into the slab and use epoxy or mechanical fasteners such as Hilti sleeve anchors, expansion bolts or another manufacturer of same. I'm sure you could template the connections, and set into the concrete, but its just as easy to drill and install later. When placing reinforcing in the slab, make sure to keep it clear of where the fasteners will go, and when sizing the slab, make sure the fasteners have enough distance from the edge of slab, as well as your base plate detail maintaining enough edge distance of the fasteners to each one. You don't want mechanical fasteners to close to each other, epoxy may not matter so much, but an expansion bolt to close to another could fracture the slab when you tighten it down. Should be a relatively easy install, just some tips to help !

When that bin is full, it's going to weigh a lot with the weight resting on small areas.
make sure you make a thick reinforced slab.

i noticed you said legs on the bin. is this a hopper bottom bin or does it have an air floor?

A sonotube at each leg would make a good footing for it, if you
don't need the slab part.

You need a thick ring where the legs go to anchor once of
those, lot of weight on the leg points with the slab. And
reinforcing rod.

I'd prefer the bolted L legs too.

Paul

It sounds like what you have is actually a bulk bin since it is 6 feet across with legs?? What I have seen with the bulk bins is to pour a 6" slab of moderately strong concrete extending a foot past the diameter of the sides. When you layout the forms dig holes immediately under where the legs will sit an additional 12 inches, since the weight is going to be concentrated. The holes could be one foot in diameter. Actually you should have a rat barrier around the entire slab, so both could be accomplished by digging a one foot by one foot trench around the slab. That would support the bin and provide rat protection. I would think that would be more than plenty to support the bin. Most 18' - 7 ring grain bins are sitting on a 6" slab with a 1' by 1' trench around the outside under the 6" slab. Fastening the bin down isn't that hard. Done several of them. Set the bin on the hardened concrete to get it centered. Either weld plates to the bottom of the legs with 1/2" holes in them or use 4" wide angle irons and bolt to the leg and concrete. Drill 1/2" holes in the concrete with a concrete bit (not that hard to do - concrete drill helps - cheap at Menards.) Then use concrete anchor bolts. 1/2" reinforcing rod every foot across sideways and then every foot longways would be beneficial as well, not to prevent cracking, but to prevent the concrete from spreading when it does crack. Make sure the re-rod is midway in the slab when the concrete is poured and out of the way were the concrete anchors will be put. Make sure you are pouring on either a soild base or tamped fill. Not that hard - 1/2 a day job.

I've poured slabs for and installed these, back then they recommended the slab be 13"thick. That was before we had the tubes you could fill with cement. Do NOT weld on the legs, it will cause them to fail. Do as Ohio 88 says, drill a hole in the bottom of the legs and bolt an L shaped piece of galv steel to each leg. We used red head anchors put in the concrete after it cured to hold in in place.

For a standing bulk bin I prefer concrete pillars instead of a slab. If I am using the auger on my mixer grinder under the bulk bin I need a little more room - a slab would be harder to work with. I also wouldn't weld on those legs. I think you are asking for trouble there.

I put up a big hopper bin a few years ago and it stll stands good.

I pored a thick slab betwee 6and 7 inches deep and used concrete with fiberglass in the mix. I drilled into the concrete and put in anchors to keep the bin upright. The reason I used a thick base is to keep the bin upright in a windstorm as I have seen some with just a 4 inch concrete base that toppled in a strong wind, pulled the base over like a tree with roots.

Coming from an engineering perspective. I would pour 4 columns with footings under them (4 sonotube piers alone isn't enough without the footings). Then, if you want a slab, put expansion foam around the columns and pour an independent slab up against the piers. The expansion foam is very important to allow for expansion and contraction of the slab. Otherwise when it expands, it will crack somewhere.

In concrete slab design, if you have concentrated loads with 4 columns, a slab tends to be put in tension in the middle due to the bin weight being applied at the 4 corners. Concrete is very weak in tension, but high in compression. Supporting the load on 4 independent concrete piers releases the bin loads from the slab and the load is transferred directly to the piers and soil. We typically call the slab in this scenario a cleanup slab which can be 4" thick unless you plan to drive a truck on it.

As far as footing, pier, and slab sizing I couldn't make a recommendation due to several factors....Wind loads, seismic loads, loads to be put on slab, and most important soil conditions make each job site requirements different.

That"s about the size wet corn holding bin I put up 25 years ago. I poured an 8 inch thick slab. The bin held 800 bushels, had 4 legs. In the 90s I replaced that with a 1600 bu bin. That"s 100,000 lbs of corn, on 5 legs. Legs slowly settled thru the slab.

Replaced it last month with 16 inch deep, 3 foot wide outer ring, 5 inch across the center, per factory specs. I pre-made the anchor rings with bolts, rebar at each leg, and set it in the hole before pouring. It does need 28 days to get full strength.

Thanks for all the suggestions!! I will defiantly will not be welding on the legs! Lot of good Ideas and and a lot of food for thought!!
Thanks again!!

Hopper bottom