I find the subject of your analysis program interesting, and would like to hear more when you have done . . .
Here in South Africa the 'scaffold tube' that is used is made from so-called 'high-yield steel', and the yield strength is 340 MPa (similar to BS Grade 50) from most manufacturers. However, you should remember that the couplers used will often cause a buckling of the tube at the load points long before this yield point is reached in simple bending.
Your BS5975 'Falsework' code of practice (esp Appendix B) may also be of help.

I had not thought about South Africa but all info is useful. I am entering the scaffold tube into a fixed database using the max bending moment In the uk we do not generally use high yield tube for tube and fitting scaffolds so I have no data. If you could give me a working stress, and a code for reference, I could add it to the database.
As for more details on the beam analysis program. I gather I am not allowed to advertise and I don't think that I can contact you direct so I can only suggest that you do a search to find my site.
Briefly the program will have lift off supports, an editable database for soldiers, ladder beams etc and the facility to use or check the moment provided by a double coupler.
Are you using BS5973 and 5975 in SA ?

Sorry that I have not responded sooner.
I do not think that it would be correct to use only one value for the bending moment limit in your program. Try a simple test : Clamp a horizontal tube between two uprights using your standard fittings and load it with planks carrying bricks etc. On a short span the tube will probably fail by crumpling at the fittings. On longer spans the deflection limits what can practically be used.
However, as a general guide, you can probably assume a yield stress of 200 to 270 MPa in the mild steel cold-formed tube before buckling occurs at the support points. For allowable-stress design methods, you would factor this by say 1.6 (non-critical apps) or 2.5 (life-critical apps) for temporary works design.
Here in SA we have a very simple and somewhat old-fashoined scaffold code of practice, so I prefer to use the BS codes for serious temporary works structures.

That's OK but I am trying to use recognised norms not define then.