Please ¿Are you know design of roofs with girders rings, rafters, columns for atmosferic storage tanks API-650? ¿Which is the procedure for calculations and designs of structural roofs?
My friend, you are in for a long calculation. The requirements relating to the supported tank roof is discussed in detail in AP!-650. If the job is an expensive one, and you can bear the cost, you could invest in a neat piece of software called TANK by COADE (Phone 281-890-4566). This programme will design the major components of the roof, including the ring girders, rafters and purlins. I have used this programme, and it works. You can also get details on their web site at
If you have (or can steal, borrow, or view) a copy of the book 'Process Equipment Design' by Brownell & Yound, there is a ton of stuff in there that will help you. The book is available at Brown Bookshop in Houston Texas for about $250, but well worth the cost.