Try SMACNA (sheet metal manufacturers?) of USA.
They have complete designs & details of ducting. There is one publication for circular ducts & another one for rectangular ducts.
I have designed some 2 m dia SS ducting using their recommendations. The saddle support design does not include saddle tip stresses (as detailed in Rouke & Young, formulas for stress & strain, AWWA M11 for steel pipelines, etc) but this is compensated for by the use of lower stresses. I don't think that this degree of detail (saddle tip stresses) for duct supported on saddles is warranted.
The SMACNA publication has been around for a long time (before 1975 I think) so obviously there is a continued use & successful experience behind it.
BarryEng