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Re: CBC CODE SR VALUE

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 Simon
The way I read this, you would have to use 100 percent of the V base shear
for regular structure and 125 percent for an irregular structure.  The
formula in 31a-1 assumes that you have a structure with a period exceeding
the transition period, ie you are in a velocity dependent curve.  The SR
value would have to be computed in accordance with 31A-2 provided you have
determined the number of modes required to get at least 90 percent
participation and the values for CBCm and MPEm and PMm can be determined
for the applicable  site specific soil.
This is a departure from the UBC that allows a reduction of Vb to .8Vb
provided you have a regular structure and 100 percent for irregular
structures but in no case be less than Vb/R.  You can see that the CBC
values are more conservative.
Samir Y. Ghosn, PE
Harris & Associates
At 03:57 PM 1/15/2003 -0500, you wrote:
>What I am aware of is that Vsc = V (SR)   (CBC 31A-1?)
>
>Vsc is the design base shear.  This seems different from the design base
>shear used in UBC Code.  I am asking this because I am gonna redesign a
>building which was originally designed by the CBC Code. However, I am not
>familiar with this Code and I need to figure out what's the design base
>shear used before as per CBC.
>
>
>
>Can you be a little more specific as to where in the CBC you are coming
>across this term or what you are trying to do with it?
>
>-gerard
>Santa Clara, CA
>
>-----Original Message-----
>From: Simon [mailto:shchao(--nospam--at)umich.edu]
>Sent: Wednesday, January 15, 2003 11:58 AM
>To: seaint(--nospam--at)seaint.org
>Subject: CBC CODE SR VALUE
>
>Hi,
>
>Is there anyone familiar with the CBC Code can tell me what's the
>definition
>of Spectral Ratio and how to determine it?  Thanks
>
>
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