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Re: Site Specific Analysis Sds and Sd1 values

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Ben,
Thank you for your response.

I wanted to add that the confusion might have stemmed from a misleading heading in the geotech report, which had a "smooth design response spectrum" which I believe was the MCE Ss vs T plot, which was not adjusted for site class D nor was lowered down to a DBE (2/3 factor).

To add to the problem, the SER has used a Seismic Design Category "C" based on the Sd1 of 0.18 and not 0.2544. Using Sd1 of 0.2544 would put them in SDC D, meaning they can't use R=3 nor design the structure "as not detailed for seismic requirement".

However, using the USGS Hazard map, the Ss = 0.42 and S1=0.09. I am not very familiar with site specific studies, but do the site specific value yield results that are more stringent than USGS maps?

Thanks
Anantha
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ANANTHA NARAYAN, E.I.
Structural Engineer
Bliss and Nyitray Inc.
Miami, FL - 33134


----- Original Message ----
From: Ben Yousefi <Ben.Yousefi(--nospam--at)SMGOV.NET>
To: seaint(--nospam--at)seaint.org
Sent: Thursday, 12 April, 2007 6:55:08 PM
Subject: RE: Site Specific Analysis Sds and Sd1 values

I am assuming youʼre referring to 2003 IBC (based on ASCE 7-02), which does not have any exceptions to calculating Sds and Sd1 per 1615.1.3. If you use 2006 IBC, which is based on ASCE 7-05 the only exception from calculating Sds and Sd1 is for simplified analysis, which is covered in section 12.14.8.1. But even with that method, you donʼt just substitute Ss with Sds. The only thing I can think of is that whoever prepared the structural notes didnʼt have much familiarity with ASCE 7 seismic provisions.

 

Ben Yousefi, SE

Santa Monica, CA

 


From: Anantha Narayan C.K. [mailto:anant_27(--nospam--at)yahoo.com]
Sent: Thursday, April 12, 2007 11:05 AM
To: seaint(--nospam--at)seaint.org
Subject: Site Specific Analysis Sds and Sd1 values

 

Greetings,

 

I have a question pertaining to computing Sds and Sd1 values from the values of a site specific analysis.

 

Here is the information.

Site Class = D

Ss = 0.48 g

S1 = 0.177 g

 

Fa = 1.42 and Fv=2.09

 

I used the procedures from IBC Section 1615.1.3 and used Sds = 2/3 Ss Fa and Sd1 = 2/3 S1 Fv to arrive at Sds = 0.4544 g and Sd1 = 0.2466 g.

 

However, in the structural notes of the job I am peer reviewing , the Ss and S1 values are reported as Sds and Sd1. Is there any place in the code that allows the use of Ss as Sds and S1 and Sd1. 

 

Any input on use of site specific geotech information to interpret design level seismic forces is appreciated.

 

Thanks

Anantha
 

VTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVT

 

ANANTHA NARAYAN, E.I.

Structural Engineer

Bliss and Nyitray Inc.

Miami, FL - 33134

 


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