Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

Re: Site Specific Analysis Sds and Sd1 values

[Subject Prev][Subject Next][Thread Prev][Thread Next]

Anantha,

The USGS maps should be pretty representative and should only deviate from a site specific study by a small amount unless you have a unique local soil condition (i.e. small local area of peat or liquefiable soil).  That said,  my experience is that very few geotechnical engineers know how to do a site specific seismic analysis correctly and in coastal California I have not yet seen one correct.

What I typically see is the geotech fills out a one sheet form of soil conditions, sends it to Berkeley where an unpaid grad student run their FRISK program, the geotech pay the University $1500 then sends it to the Architect with a bill for $3000, then the Architect sends it to the structural engineer and bills the client $5000.

Thomas Hunt, S.E.
Fluor



"Anantha Narayan C.K." <anant_27(--nospam--at)yahoo.com>
04/12/2007 04:17 PM
Please respond to seaint
To
seaint(--nospam--at)seaint.org
cc
Subject
Re: Site Specific Analysis Sds and Sd1 values





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

VTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVTVT
 
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 you’re 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 don’t just substitute Ss with Sds. The only thing I can think of is that whoever prepared the structural notes didn’t 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

 



Yahoo! Mail is the world's favourite email. Don't settle for less, sign up for your free account today.




Yahoo! Answers - Got a question? Someone out there knows the answer. Try it now.


-----------------------------------------------------------------------------------------------------
The information transmitted is intended only for the person
or entity to which it is addressed and may contain proprietary,
business-confidential and/or privileged material.
If you are not the intended recipient of this message you
are hereby notified that any use, review, retransmission,
dissemination, distribution, reproduction or any action taken
in reliance upon this message is prohibited. If you received
this in error, please contact the sender and delete the
material from any computer. Any views expressed in this message
are those of the individual sender and may not necessarily reflect
the views of the company.
-------------------------------------------------------------------------------------------------------