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RE: Old Seismic Values

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I've basically decided that the "maximum effective peak acceleration of 5%
of gravity" is the local "exact" value for the UBC Z variable, which is peak
ground acceleration on moderate rock.

Actually, I have 5 values for "Peak Ground Acceleration" for this site:
1997 UBC:   7.5%, 10% exceed in 50 years (475 yr. return)
Old Report: 5.0%, 10% exceed in 50 years
2002 USGS:  2.13%, 10% exceed in 50 years
2002 USGS:  6.25%, 2% exceed in 50 years (2475 yr. return)

I also have "Spectral Acceleration" values from 2002 USGS.

But I'm still stuck on the "peak velocities of 1.5 inches per second" part.
Where does this come in?

I realize that you high-seismic folks are picking yourselves off of the
floor from laughing so hard at such low values.  The only reason I'm even
remotely concerned about this is that it's a federal MILCON, and the fed
people in charge have SPECIFICALLY stated that seismic upgrades are a high
priority.

What I need to do is summarize the different force levels and have the Owner
pick the preferred level of upgrade required, or realize that no upgrades
are necessary.  To do this, I need an "apples to apples" comparison,
preferably independent of soil and "R" values.  To do that, I need to
convert the "peak ground acceleration" values to numbers I can put a single
equation such as:

Acceleration * Soil Factor * Weight / "R" value

The soil, weight, and "R" should all be the same, which means I can't use
the 1997 UBC for two values and TI-809-05 for the other 2.

Any ideas?

---
Jason Kilgore
Leigh & O'Kane, LLC
Kansas City, Missouri

> -----Original Message-----
> From: Dmitri Wright [mailto:dmitri(--nospam--at)pciengineers.com]
> Sent: Wednesday, August 11, 2004 11:09 AM
> To: Seaint
> Subject: Re: Old Seismic Values
> 
> Jason,
> 
> I think the key word that is missing from your description is "spectral".
> Peak GROUND acceleration or velocity is different than the peak SPECTRAL
> acceleration or velocity.  It sounds like the information in the report
> you
> were given was for peak ground values.  Aa, Av, Ss, & S1 are spectral
> values.  The theory is that an ideal oscillator (think of a bowling ball
> on
> a thin steel rod stuck in the ground) with a particular fundamental
> frequency will experience a certain peak acceleration and velocity in a
> given seismic event.  These accelerations and velocities, which are the
> spectral values,  will be different for oscillators of different
> frequencies, and will be different from the values at the ground surface.
> Aa & Ss are the values for an oscillator with a 0.2 sec. period (period =
> 1/frequency).  Av & S1 are for an oscillator with a 1 sec. period.
> 
> In the older UBC, Z is the approximate peak ground acceleration.  0.2
> spectral acceleration is approximately Z*C with C=2.75.  The 1.0 spectral
> acceleration is approximately Z*C with C calculated for T=1.0 => C=1.25.
> 
> Of course, all these values vary depending on the confidence level.  The
> current codes use a 2% probability of exceedence (98% confidence) in 50
> yrs.
> I'm not sure what the older UBC values were based on.  Up to date values
> for
> any location in the US are available free at http://eqhazmaps.usgs.gov/.
> 
> The FEMA 273 or 368 commentaries, or the ASCE7 98 or 02 commentaries have
> very good information on this subject.
> 
> I hope you send a summary of your (general) findings to the list, once you
> have finished your investigation.  This is a very relevant topic that most
> structurals, at least in the west, will be dealing with for years to come.
> 
> Dmitri Wright, PE
> Progressive Consultants Inc.
> Portland, OR
> 
> 
> --------------------------------------------------------------------------
> From: "Jason W. Kilgore" <jkilgore(--nospam--at)leok.com>
> To: <seaint(--nospam--at)seaint.org>
> Subject: Old Seismic Values
> 
> I have a project in a low/moderate seismic zone (moderate to high wind), =
> and
> the client specifically wants seismic calculations and details.  I was =
> then
> given this information as part of a larger report:
> 
> 
> "The site is in seismic zone one (1).  However, the area is free of =
> major
> active fault structures and the region is relatively free of seismic
> activity.  According to recent investigations, the area will experience
> seismic forces with a maximum effective peak acceleration of 5% of =
> gravity
> and effective peak velocities of 1=BD inches per second during any =
> 50-year
> period, at the 90% confidence level."
> 
> 
> The 50-year/90% confidence is the design level in the UBC codes and the =
> 1991
> NEHRP / ASCE 7-95.  I'm pretty sure I know what "maximum effective peak
> acceleration of 5% of gravity" and "effective peak velocities of 1.5 =
> inches
> per second" mean.  However, is there a relationship between these =
> numbers
> and UBC design values?  What about Aa and Av (older NEHRP)?  Ss and S1
> (current NEHRP)? =20
> 
> Any guidance as to where to look?
> 
> Specifically, I would like to give the client a comparison between the
> values they gave me and values from FEMA 450/2003 NEHRP (Ss =3D 14%, =
> S1=3D6%).
> 
> Thanks in advance.
> 
> ---
> Jason Kilgore
> Leigh & O'Kane, LLC
> Kansas City, Missouri
> 
> 
> 
> 
> 
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