SOLIDWORKS Design & Help

16mm will do fine

3/4" thickness minimum, and make sure that the person who assembles the structure has experience in structural welding, that is very important, even if you use plates of greater thickness, the quality of the welding is very important, I can suggest the use of laboratory and x-rays to ensure quality and integrity of your structure.

i think Angel Ramirez is right about the welding quality, but i still thinking 16mm thickness is enough if you do good work on design.

Thanks

I have designed H type and C type both (Structure)

make c type and give rib 14-16mm is enough

Add corners plate if you are not sure