Hi fmdiazlopez,

A silo is like a paper bag, or a sack full of sugar. As long as it it full you are OK. It is only when you start to empty it that you might get into trouble with the bag collapsing.

If you ask the question - how thick should I make it? - the answer is easy - just use your hoop stress formula. Assume the contents is a liquid of equal density and you will be OK. In steel we don't go less than 6 mm, with say 8 mm for the bottom strakes. But that approach won't give you the cheapest solution.

If you ask - how thin? - then you leave the land of water and petrol tanks, and venture into the new world of bulk solids handling. The atmosphere here is completely different. We look at membrane forces, shell buckling, smile buckles, mass flow, rat-holes, eccentric discharge, and other magic stuff.

The Australian Standard is a good place to start. So is the British Iron & Steel Institute. The Canadian Codes are great, particularly in post-tensioned concrete.

Its a whole new world out there mate.

Regards - Sgt John.Rz

www.latviantourists.com.au / Open Book Club / Files / Bionic Research Institute ■

Hi shipmates,

Sound advice there - but don't try to apply it to the grain industry. They use corrugated sheet metal 1.5 mm thick or so.

The problem with local Codes is - there ain't none. I was working on design for construction in the Congo. Design to FIFO standards they said. Use South African Codes they said. But base everthing on Australian standards they said.

And the site supervisor speaks French, and the foreman communicates in Swahili.

So I Googled. I found out that FIFO isn't a set of standards - its an association of International Consulting Engineers - so anything goes.

South African Standards are top class. But in the Copper Belt most everything is done to Anglo American standards. And how well do the Swahili-speaking Congolese know Australian Rules and Regulations? They don't even know that we now mix concrete using a set of scales - not so many wheelbarrow loads [no wonder they can't produce better than 20 MPa concrete].

I was told that it don't much matter what you specify, the site crew will build it by the seat of their pants anyway. So I decided that, as much as practical, everything needed to construct the job must be stated on the working drawing.

Regards - John.Rz ■

Hi fmdiaz,

I've just had a look at your calculations.

Pay some pesos to an experienced Senior Engineer. Then you will be able to sleep at night. Your company can afford it anyway - and it's a lot safer than allowing you to take professional liability for something you don't really understand yet.

Learn by watching what Senior Engineer does, and google the information Lyle Brown has shared with us.

If the truth be known, the "Powder/Bulk Portal" is the wrong forum for your question. Try the US version on www.eng-tips.com . Then you can talk to structural engineers who design tanks and silos for a living.

Regards - John.Rz ■