# RE: Question on "Seismic Zone Factor" (Z) in UBC

• To: "'seaint(--nospam--at)seaint.org'" <seaint(--nospam--at)seaint.org>
• Subject: RE: Question on "Seismic Zone Factor" (Z) in UBC
• From: "Sherman, William" <ShermanWC(--nospam--at)cdm.com>
• Date: Thu, 25 May 2000 13:30:00 -0400
```"Z" does represent an approximate "effective peak ground acceleration" such
that Zone 4 relates to 0.4g ground acceleration. However I would view Z as
being similar to a Basic Wind Speed. Design for a specific location for wind
depends on various adjustments (such as due to Exposure classifications) to
the wind stagnation pressure which is directly related to Basic Wind Speed.
Similarly, seismic design depends on modifications to the Z-factor such as
due to soil type and near-source faults. I would say that Ca and Cv obtained
from the 1997 UBC tables represent the effective design ground acceleration
for a particular site.

Thus if Ca=0.24, the effective design ground acceleration is 0.24g =
0.24x32.2 ft/s^2 = 0.24x9.81 m/s^2.

-----Original Message-----
From: seaint-return(--nospam--at)seaint.org [mailto:seaint-return(--nospam--at)seaint.org]
Sent: Wednesday, May 24, 2000 11:46 AM
To: seaint(--nospam--at)seaint.org
Subject: Question on "Seismic Zone Factor" (Z) in UBC

This is a questions regarding seismic design under the Uniform Building
Code.

It is my understanding that the magnitude of the seismic zone factor (Z) in
the UBC is equal to a fraction of the acceleration due to gravity
(9.81m/s^2).  As a practicing Canadian engineer in Edmonton, Alberta, I am
not really familiar with UBC and would appreciate feedback from someone who
is familiar with this code.

Please confirm that the relationship between design ground acceleration (in
m/s^2) and "Z" is simply the design ground acceleration divided by
9.81m/s^2.

```