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RE: Site Accelerations

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You REALLY want to put me on the spot.

This was a point of major consernation, debate, cussing and discussing in 
the ASCE 7 process.  This is one of those connection issues.  The various 
sections of the IBC invoke various sections and issues of the ASCE 7.  The 
ASCE 7 draws from the NEHRP various documents.  There was a huge change 
that came into the ASCE 7-10.  (Preview: There will be more subtile changes 
 in teh ASCE 7-10 Suppliment)

The ASCE 7-10 changed from the Maximum Considered Earthquake (MCE) to the 
Maxium Considered Earthquake Risk Targeted (MCER).  The probability went 
from a 2% chance of exceedance in 50 years for the MCE in the ASCE 7-05 to 
a 1% chance of exceedance in 50 years for the MCER in the ASCE 7-10.

It all boils down to the risk of collapse for a given seismic event.

RE: The ASCE 7-10, Section C 11.4 presents this in general terms.

This is one of the papers that generated all of the excitement. 
<>  The 
paper was written for the 2007 SEAOC convention, but I am sure that most 
engineers did not realize the implications.  Once it became the building 
code, engineers were hit with the reality of ground motions going up.  In 
some places the ground motions went down due to refinements in the mapping, 
 source characterization, and attenuation.  But in general, the ground 
accelerations went up.  Nico Luco was the primary author and one of the 
smartest guys I have had the priviledge to know.  The other authors are 
brilliant guys that most everyone will recognize.

Regards, Harold Sprague

> Date: Wed, 28 Nov 2012 11:01:12 -0800
> From: Tarekmokhtar(--nospam--at)
> Subject: RE: [SEAINT-SEAOSC] Site Accelerations
> To: seaint-seaosc(--nospam--at)
> O.K Harold, inquiring minds want to know :)
> Tarek
>> I get the similar response when I checked my last year's project done
>> with IBC 2009. Same project with IBC 2012/ASCE 7-10 yielded 30% lesser
>> Sds ground motion. Harold, is there an explanation for lower values?
>> Mansoor Khan
>> -----Original Message-----
>> From: seaint-seaosc(--nospam--at) [mailto:seaint-seaosc(--nospam--at)] 
>> On Behalf Of Tarek Mokhtar Sent: Tuesday, November 27, 2012 3:15 PM
>> To: seaint-seaosc(--nospam--at)
>> Subject: RE: [SEAINT-SEAOSC] Site Accelerations

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