Happens all the time, depending on how good the witchcraft is of your geotechnical consultant.

I suggest you post your query in the "Structural Engineering" area for a higher possibility of generating additional comments.

I have designed many corrugated steel silos' foundations and haven't had any problems, probably because I take appropriate values on allowable bearing stress to limit settlement, the secret is there.

Settlement is OK.  Differential settlement is NOT.

   Going the Big Inch!
http://virtualpipeline.spaces.msn.com

Hi,, thank you for the comments back on bins.

In the past 25 years, we have designed foundations for perhaps 2000 bins and tanks.  It's a big part of our business.  With the ever taller and larger bins and tanks being sold in the industry, some of the sites are not on very good natural soils.  We find that soil test company recommendations and predictions are sometimes really not very accurate when it comes to total settlement and differential settlement.  We do great designs for downward settlement, with slipjoints, etc. on catwalks, spouting, etc..... We work with the soils test companies to let them know what we think is acceptable total and differential settlement for specific bin sizes, heights, etc.    Boy have they missed on their "guesses" a few times lately.. We, for sometime, have been putting it writing to all contractors, owners, test companies, etc. involved in a specific bin job that the soil test information will be used in the bin foundation designs but if settlement and differential settlement in excess of predicted occur, we all will be talking to the soil test company as it is not the contractor or engineer's problem!!! By the way, we have walked away from more than a few jobs over bin bearing and what we considered bad soils and bogus soil test recommendations..

r

r

What I used to do with large process vessel foundations and pellet silos and still do today with large pumps, compressor foundations and tanks is to get copies of the boring logs, from all four corners and one in the middle, if its a large area that will be loaded.  If there is any difference between soil layers or lenses, watch out.  As I say, you can design for settlement, as you have well learned, its the diff settlement that's very problematic.  In some extreme cases, I've had to excavate poor material to 40 ft. depth and backfill with compact sand-cement mixes and even used stone columns to 60 feet depth in one case.  Then there's piles...

   Going the Big Inch!
http://virtualpipeline.spaces.msn.com

... and pumping in lime slurries.... and other witchcrafts.
       

   Going the Big Inch!
http://virtualpipeline.spaces.msn.com

Part of the problem seems to be that many grain bin/tank owners, contractors and  jobs can tend to be pretty farmie and everything has to be cheap.... piling, helicals, large over excavations and backfilling makes the clients and contractors really "pucker"...  cheap, has to be cheap... but when something goes wrong!!! it gets interesting..

With grain bin/tanks,, we recommend not using wall side discharge systems because of eccentric loading on the tank walls and soils beneath....    The bin manufacturers all have me/to and follow the crowd and provide wall side discharge hoods and flume systems....  Using such systems will place eccentric loads on the soils and can cause/aggravate differential settlement and tipping problems.

Once a bin has been completely center drawn down... other floor gates can be opened in turn and completely emptied working from the center out...   after any gate other than the center of floor gate has been opened, the bin should be completely emptied before being refilled,,  We show all gates other than the center of floor gate padlocked tightly shut.. with the instructions and keys given to the Owner...

r

Wow.  I don't know if I'd trust them to do all that.  I have troubles just getting the generator tanks filled every day at 16:00 hrs.  They're always running round in the dark at 21:15 trying to fill them.

Sounds like side wall load is pretty severe in that it acts like an eccentric dead load and that makes it hard to use an increased soil live load bearing capacity to keep fdtn size down, but if you only use dead load capacity, the fdtns get ugly pretty quick.

I think I'd be thinking of programing some PLC to monitor the loads and auto lock the gates.  Maybe some controls engineer wants to invent one for you.  Heck, maybe I do.

   Going the Big Inch!
http://virtualpipeline.spaces.msn.com

Have others been noticing an increasing number of corrugated steel bin failures due to long term corrosion?

Does anyone have suggestions for references and standards regarding temporary bracing of corrugated steel grain bins during assembly, jacking and erection work.

r