External rafters fixing

[Mindaugas_Kukis]

Hello, Experts,


I have question regarding external rafters for rafter supported cone roof. Had a project where stainless steel tank was designed but they wanted, for price cause - to do external rafters from carbon steel. When the rafters are inside, the end in shell side I make UPN beam inside with plates around the shell to fix rafter ends and in the middle of the cone - construction from plates and profiles similar as shell side with plates.

Searched the internet about solutions for rafters fixing from the outside in ends (shell side, cone center)- can't find any examples. Could you share some? As I've seen it's good as well for tank roofs with internal coating to have rafters from outside. In these cases tanks are insulated, the ones I investigate, so no problems with water accumulation on roof.

 

[JStephen]

Typically, just bring the rafter ends very near the outside edge of the roof plate, and both are set on top of the top angle.
With carbon steel/ stainless steel composite, you may get some effects from differential thermal expansion, as well as some corrosion considerations.
Normally, the design assumption made is that the compression flanges of rafters are laterally supported by the roof plate. If the rafters are on the top side, that is no longer the case, so you do have some design considerations there as well.