Code Based Target Spectra

03-Unexpected behaviour/errors
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Joined: 22 Jul 2011, 10:19
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Code Based Target Spectra

Post by huffte »

When I select ASCE 41-17 as the code for spectra generation, the requested input is SXS, SXL, Damping, Site Class, and transition period TL.

I believe that SXL should actually be SX1?

In ASCE 41-17, SXS and SX1 already have site effects incorporated. So, it appears that site effects are being applied twice as currently exists in the spectrum generation.

It also appears that the damping correction may have an issue, but this may fix itself when the site effect apparent issue is resolved.

Given that site factor research is heavy right now, and that site factors are changing, it seems best to me to leave the site factors up to the user and have them input SXS and SX1, as currently specified. This would allow you to eliminate the need for the user to specify a site class and would eliminate the need to keep the software updated to match current site factors.

I believe this would be the preferred method. That is, let the user worry about the site factors and have them input SXS and SX1. Then make sure that the damping adjustment is correct, according to ASCE 41-17 equation 2-3 (it should be 1 when damping is 5%, and I am not sure that is currently the case).

These comments apply to SeismoMatch as well. Both are sooooo useful!!! Thanks very much.
Tim Huff
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Joined: 06 Jul 2007, 04:55

Re: Code Based Target Spectra

Post by seismosoft »

Indeed, SXL is meant to be SX1. We misread SX1 (i.e. the spectral acceleration response at 1-sec) to SXL (that is the spectral acceleration response at large periods - as opposed to SXS which is the spectral acceleration response at short periods). We will fix this in the next release of the programs.
Many thanks for noticing this, Tim.
Seismosoft Support
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