"Rules of thumb" for column roof layouts 1

[Motorspirit]

Hi All

I am designing a 36m tank where the client requires a column supported roof. I am doing the preliminary layout for the roof members and wondered whether there were any industry rules of thumb for layouts that lead to efficient designs, ie:

Max spacing between circumferential collector beams to keep radial rafter sizes practical. It seems to me this number should be kept to around 4-5m. Ie for 36m tank if I use 3 x equi-spaced circ collectors can limit span of radial rafters to 4.5m.

Max spacing of column centres to keep collector beam sizes practical. Seems 6-8m would be practical here?

Layout of columns; Obviously the max span of collector beams will set this distance in the outer most "ring" Are there any rules of thumb for how to lay out the inner ring columns in relation to this ??

Also: Is it typical to keep the roof angles low and allow the radial rafters to be welded directly to the circ collector beams or are cleats normally used for this attachment??

Appreciate any feedback from those who have done a few of these.

Cheers

 

[JStephen]

It varies somewhat by fabricator, based on materials available, erection equipment used, etc. Typical rafter lengths are 25'-30', based on available lengths stocked by service centers (they actually stock 40', 50', 60', which are cut in half). Typical circumferential beam lengths are 25' or so, and once again are adjusted to minimize waste based on available sizes. Even for companies that have done this for years, they may come up with different arrangements as conditions change.

On the welding rafters to beams- it is done both ways. Probably some form of chair is more common.