API 650 Appendix E

[vibrasie]

In API 650 Appendix E, what is the basis for using a factor of 1.5 for adjusting the spectral accelerations from 5% to 0.5% damping?
What other method may be used to establish the spectral acceleration at 0.5% damping given a response spectrum at 5% damping?

 

[JStephen]

Googling "Seismic damping factor" pulls up a number of technical papers on the topic, but I don't see anything specifically on the 5% to 0.5% change. (The emphasis is going the other way where intentional damping is present, it seems.) The 1.5 factor is also incorporated into AWWA D100, etc, so it's not specifically an API thing.