Adjusting spectral acceleration to a different damping ratio

[vibrasie]

In API 650 Appendix E, a factor of 1.5 is used to adjust the spectral accelerations from 5% to 0.5% damping. No explanation is given why this is valid. What method may be used to establish the spectral acceleration at 0.5% damping given a response spectrum at 5% damping?

 

[structSU10]

The best method is to recalculate the response spectrum for the actual damping present. In general, damping just leads to faster attenuation of dynamic response, and reduces the resonance effect on a structure.

here is a paper that evaluates the factors however, and it explains how it is appropriate:

http://peer2.berkeley.edu/ngawest2_wg/wp-content/uploads/2010/09/Naeim-Kircher-2001.pdf