Making my own rear strut brace

[lolsteve]

Most applications for I-beams see very little torsional stress, so the stiffness isn't an issue, for a strut brace connecting to one side of a tower, it very much is.

Just use some tube.
And don't do the normal trick (and the same as the first link), and make the transistion from your stiff beam to a weak, floppy plate happen in 1mm, all that does is concentrate the stress there and make it flex on the joint.
That why my braces run tube all the way to the bolts.

So make sure the tube overlaps the plate somewhat? and up to the top bit as much as I can like this? It's crude but the idea is there . What thickness plate as a minimum would you recommend if it was just a cheap steel grade?