Seismic design for Dome roof rafters

[thiru777]

Hello all,

Is seismic design required for individual members (rafters) of a dome roof supports in API 650-tank? The rafters are now designed for live load, dead load and wind loading. If seismic is mandatory for roof support design kindly provide any reference for the same.

 

[msquared48]

I do not know of a specific reference in API-650, but since the dome roof is a structural diaphragm, it transmits any lateral force to the side walls, including seismic. So, yes, if seismic controls over wind, it would be required to be designed for.

Mike McCann, PE, SE (WA)

 

[JStephen]

If the rafters are attached to the roof plate, then lateral forces can be resisted largely by the roof plate itself. I would assume that seismic design was required unless exempted somewhere, rather than asking for a reference to require it, but in many cases, that analysis would be fairly simple, given the support by the roof plate.