Application of Seismic Load on Large Steel Framed Dome?

[Screwtape]

We are currently doing a structural analysis of the roof framing for a large dome (diameter=265'). The dome was constructed around 1965 and the roof framing consists of steel frames, rings, and secondary beams with a cementitious (Tectum) roof deck.

The primary ribs/frames are radial and occur at 10-degrees OC. There are 5 concentric rings with the centermost ring being identified as a "Compression Ring" and the outermost/perimeter ring is identified as the "Tension Ring". Secondary framing consists of small radial WF beams. See attached RISA model views for a general layout.

Up to this point, I've been unable to find any info or documentation regarding application of the seismic load on a dome structure such as this. I'm comfortable with the magnitude, but uncertain how to accurately and realistically model the seismic force.

Any ideas or thoughts? Any links or references would be great. Just point me in the direction.

 

[msquared48]

I would lump the seismic load at many nodal points rather than just a few here at the rings and apply them in one direction. Unfortunately, this will take a lot of time, but I think you will get a more realistic result.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[Screwtape]

At this point, the seismic forces have been modeled as point loads at the top of the columns only. Surprisingly, it does fairly well, although half of the columns become overstressed.

 

[JAE]

Seismic forces always come from mass. Where the mass is will be where the forces should be placed.

 

[PMR06]

I assume you have area or dist loads for gravity dead load. Could they be copied and direction changed to some kind of lateral seismic?

 

[JLNJ]

I would think getting the loads over to the top of the columns will be where the difficult analysis is.