Kentucky S1 and Ss values all reduced in new code KBC 12

[ohioEIT]

I do a lot of work in Kentucky and the new KBC '12 is taking effect soon. Kentucky models their code after the IBC and provides a tabulation of their own S1 and Ss values categorized by county. The new version of the KBC is modeled after the new IBC and therefore ASCE 7-10.

The tabulation of spectral response numbers in the Kentucky code are reduced drastically in the new version. How is this possible? I know that the wind calculation got "re-arranged" in the new ASCE 7-10. Is it possible that the seismic provisions did as well, and this is an attempt to react to that?

I'm really just very curious at how a physical property of the geology can just all of the sudden change.

 

[UcfSE]

The physical property doesn't change. The data set and analysis we use to estimate that physical property can change, or be enhanced, or grow, and so on.

 

[ohioEIT]

I guess I was being obtuse when I suggested the physical property had changed. It makes sense to me that the estimation of those properties can change as you described.

Do you have an opinion on why that may have happened? It's not often a design resource/guideline/code/method gets less conservative over time.

 

[wannabeSE]

ASCE 7-10 uses new seismic maps. Have you compared Kentucky's tabulated values with the maps in ASCE 7-10 or the USGS utility at

http://earthquake.usgs.gov/hazards/designmaps/usdesign.php

. I know some areas in California will have higher S1 and Ss with the maps referenced in ASCE 7-10

 

[ohioEIT]

Thank you, I didn't notice that the maps had changed in IBC 12 and ASCE 7-10. The utility you provided a link to includes the new maps and returns numbers in line with what the KBC 13 has tabulated. I use the USGS java application, but according to their website, it has not been updated for the new maps. Another thread I found around here said that a lot of the contours were reduced by about 10% while select high-risk areas increased.