Safe Shutdown Earthquake
Safe Shutdown Earthquake
(OP)
I'm working on a prefabricated room for a nuclear facility in a relatively low seismic area in the lower 48. At least per ASCE 7-05. The specs indicated using a Safe Shutdown Earthquake loads with spectral accelerations as follows:
Horizontal = 3.5154g, Vertical = 1.179g.
This is where my question comes in. Normally, seismic forces would be determined using Ss, S1, site class, etc to come up with a base shear. (V=cs * W). How do the spectral accelerations given in the spec play into deriving the seismic forces. Do I use the Horizontal spectral acceleration that was given as my Ss or S1 value?
Any thoughts are appreciated.
Horizontal = 3.5154g, Vertical = 1.179g.
This is where my question comes in. Normally, seismic forces would be determined using Ss, S1, site class, etc to come up with a base shear. (V=cs * W). How do the spectral accelerations given in the spec play into deriving the seismic forces. Do I use the Horizontal spectral acceleration that was given as my Ss or S1 value?
Any thoughts are appreciated.






RE: Safe Shutdown Earthquake
I think that they are asking you to design your structure for a 3.5 g's horizontal aceleration regardless of the structure period (and 1.2 g's vertical). The horizontal force (Fi) you should apply for each floor diaphragm is: Fi = acel x tributary weight.
In a way it's a kind of Cs factor. If I'm not wrong is like having a constant response spectrum.
Nevertheless it looks like a very conservative design, meaby this is because it's a nucler facility. Regards,
Sebastian
RE: Safe Shutdown Earthquake
However, rather than thinking of this as a constant response spectrum, think of it as the upper limit for the portion of the spectra that is for low periods or very stiff structures.
Regards,
![[pipe] pipe](https://www.tipmaster.com/images/pipe.gif)
Qshake
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RE: Safe Shutdown Earthquake
Another factor to consider is that not all SSE are even seismic events. In BWR's there were all kind of pipe break and SRV events that caused building accelerations. There's a lot of energy being tossed around in a nuclear power plant that can shake and bake the whole plant.
I'd jsut the values they give you and not try to analyze to much into it.
RE: Safe Shutdown Earthquake
I designed the pipe break anchors for a BWR and I was amazed at what it took to hold them, huge even by power plant standards.
Michael.
Timing has a lot to do with the outcome of a rain dance.
RE: Safe Shutdown Earthquake
they usually reference PGA and not Ss or S1 since Ss and S1 were developed to correspond with a 2 and 10 story structure. most nuclear structures are "short" and rigid...therefore PGA at/near zerio period is more appropriate. that statement is neither always true nor completely accurate but it is what it is for now.
see asce4 or asce 43 or some of the nuregs or nrc design manuals. maybe http://ww
RE: Safe Shutdown Earthquake
As for low seismic area. Yes, per ASCE7-05, the Ss and S1 are very low. The accelerations I was given in the spec are very big and significant. That's why I was having such a hard time justifying the use of the accelerations.
Thanks for all the responses.
Ryan
RE: Safe Shutdown Earthquake
RE: Safe Shutdown Earthquake
Jed is right. TVA requires that peak accelerations be multiplied by 1.5.
Thanks for everyone's input.
RE: Safe Shutdown Earthquake