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Re: site specific spectrum vs. published curves

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It would be helpful to have more information, regarding: (a) what is the location, and on which FEMA map are you on?; (b) are you in a high seismic area?; (c) are you in California?; (d) are you near "active" faults or potentially active faults?; (e) what is the purpose of the structure? and the Seismic Design Category? (f) could it experience a M 7 or greater earthquake?; (g) what kind of seismic-force-resisting- system will you be using?; (h) who has specified that FEMA 302 / 303 be utilized?; (i) what is the penalty for OOOPS! - failure?

If the structure could experience a M 7 earthquake, there will be more long period energy thrown at your structure; than if a much smaller earthquake was assumed in generating the response spectrum.  So it's important to consider this if you are building a structure with a longer period response.  In high seismic areas, it's never been quite clear to me what the economy would be in shaving the design parameters to the minimum, based on a site-specific response spectrum; given that the structural system is generally only 10 - 20% of the total cost of the building.  Does the client want the "cheapest the code allows?"
 

James Bela

Oregon Earthquake AwarenessTM        /        The Quake NorthwestTM
"We Have Nothing To Fear But Shear Itself"        /        "We're All Subducting In This Together"
 
 

"Khosrownia, Ghassem SPK" wrote:

Situation:
Site specific response spectrum is available for a site where an existing
irregular structure requiring dynamic analysis had to be evaluated a few
years ago. A new building is to be built in the same vicinity now. Seismic
criteria is in accordance to FEMA 302 / 303.

Question:
If the site specific response spectrum indicate ground accelerations less
than the map values published by FEMA would you think the available site
specific response spectrum (assuming it is reliable) would be a good source
to do seismic design? I think FEMA's acceptability criteria is no less than
70% of the published map values regardless of the site specific response
spectrum.

Thanks for your thoughts.

Ghassem Khosrownia
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