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RE: Old Seismic Values

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I tend to agree with Harold, "I don't know why you are even trying to use
the old data.  The old site
specific reports that were used to develop the seismicity at a specific site
are as wrong as the UBC zones were."  But I do understand your dilemma with
the client.  It's like trying to explain to a client why we are designing to
a 110 mph wind when we used to design for 90 mph, and the highest speed they
have ever seen reported on the news is 70 mph.  The method of measure and
the reliability of the numbers makes good sense from a scientific point of
view, but it is a little hard to sell to the layman.
It sounds like the work you are doing for this client fits exactly with a
FEMA 310 Seismic Evaluation of an existing building.  I think ASCE has
adopted this document as ASCE31, and charges for it.  This document gives a
very straight forward method for determining the seismic risk at your site.
Then it gives a performance based approach for evaluating the hazards to
your structure.  This is a rational approach, based on the best science
available today, rather than an arbitrary choice between different
historical values determined by different methods.  Because the FEMA values
are less conservative than the values from the "golden" old report, it
should be fairly easy to sell to the client.
I can e-mail you a copy of the (FEMA310) document and an example report if
you contact me directly.

Dmitri Wright, PE
Progressive Consultants Inc.

From: "Jason W. Kilgore" <jkilgore(--nospam--at)>
To: <seaint(--nospam--at)>
Subject: RE: Old Seismic Values

> I don't know why you are even trying to use the old data.

Because the client said, in effect, "Thou shalt use this document in your
design".  The document specifically states the acceleration and velocity
values I gave earlier.  I *know* that the values are wrong; my problem is
that I have to explain to the client why they're wrong, how much they're
wrong, what are the right values, and why they are the right values.

In order to do this efficiently, I need to completely understand exactly
what the old values are, and how they relate to the new values.

Again, I realize that these are very low numbers, but the difference in the
report value (5%, 475 yr. return) and new values (2.1%, 475 yr. return)
could mean the difference between adding bracing to all mechanical units or
strengthening existing 20' tall URM shear walls (in plane and out-of-plane).

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

Subject: RE: Old Seismic Values

I don't know why you are even trying to use the old data.  The old site
specific reports that were used to develop the seismicity at a specific site
are as wrong as the UBC zones were.  There are no good analogies from UBC
Zones to seismic spectral ordinates.  The old seismic zones vs. the new
spectral ordinates can be off as much as a factor of 12.  I think that you
might have an old DOE Facilities Natural Hazards Assessment seismicity
study.  The methodologies that were used to develop that document and other
1990's seismicity are long since out of favor by the seismology community.

Read the commentary in the NEHRP to help get a better understanding of what
was done, and what is the current practice.  The 2003 NEHRP is the best that
there is.

The old codes were more swayed by political concerns than science.  The
Nemaha Anticline at first had no effect on Kansas City (1982 UBC).  Then it
did effect Kansas City (1985 UBC).  Now it does not effect Kansas City (2000
IBC).  What really happened was an effort by seismologists and engineers to
develop standard methods (logic tree, probabilistics, deterministics, etc.)
to characterize and quantify ground motion more accurately.

Harold Sprague

>From: "Jason W. Kilgore" <jkilgore(--nospam--at)>
>Reply-To: <seaint(--nospam--at)>
>To: <seaint(--nospam--at)>
>Subject: RE: Old Seismic Values
>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
>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
>What I need to do is summarize the different force levels and have the
>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

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