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# RE: Old Seismic Values

• To: <seaint(--nospam--at)seaint.org>
• Subject: RE: Old Seismic Values
• From: "Jason W. Kilgore" <jkilgore(--nospam--at)leok.com>
• Date: Wed, 11 Aug 2004 15:52:29 -0500

```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
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%).
>
>
> ---
> Jason Kilgore
> Leigh & O'Kane, LLC
> Kansas City, Missouri
>
>
>
>
>
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