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

• To: <seaint(--nospam--at)seaint.org>
• Subject: RE: Question on "Seismic Zone Factor" (Z) in UBC
• From: seaint-return(--nospam--at)seaint.org
• Date: Thu, 25 May 2000 09:29:40 -0600
```Bill, Todd, and Jake:

Thanks for responding to my cry for help.  I too think that Z (seismic zone
factor) itself may not exactly be the ground acceleration divided by g
(9.81m/s^2).  Although the code seems to read this way, it does not
explicitly say this.

Regardless of the true definition or meaning of Z, my real problem is how to
properly do a seismic design when all the information I have about the site
is a design ground acceleration.  The UBC uses "zones" which must have
definable ground acceration limits.  What I really want to find out is what
these accel limits are for the various zones (1, 2A, 2B, 3, and 4).  Once I
can place the design ground accel into a zone then the rest falls into
place.  It's this first step that I have no knowledge of.

-----Original Message-----
From: Bill Allen [mailto:Bill(--nospam--at)AllenDesigns.com]
Sent: Thursday, May 25, 2000 8:02 AM
To: seaint(--nospam--at)seaint.org
Subject: RE: Question on "Seismic Zone Factor" (Z) in UBC

Z is still used in the 1997 UBC. See table 16-I and Equation 30-7.

But I believe it is too elementary to consider Z as merely the ground
acceleration although it appears that way. Possibly a closer evaluation
would be Z modified by near source factors.

Regards,

Bill Allen, S.E. (CA #2607)
ALLEN DESIGNS
Laguna Niguel, CA
http://www.AllenDesigns.com

||-----Original Message-----
||From: Jake Watson [mailto:jwatson(--nospam--at)inconnect.com]
||Sent: Thursday, May 25, 2000 6:36 AM
||To: seaint(--nospam--at)seaint.org
||Subject: Re: Question on "Seismic Zone Factor" (Z) in UBC
||
||
||	What version of the UBC are you using?  The "Z" is
||antiquated and
||merely in the new codes for reference.  Correct me if I am wrong (I am
||way out on a limb in my knowledge) but in the 94 UBC things
||changed and
||"Z" was no longer used in the base shear calc.  The current ('97) base
||shear calc is V=(Cv*I)/(R*T).  If you divide V by "g" then
||you will have
||the design acceleration.
||
||Hope this helps
||Jake Watson, E.I.T.
||Salt Lake City, UT
||
||> Wayne Stewart wrote:
||>
||> 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.
||>
||> Thank-you.
||>
||> Wayne Stewart, E.I.T.
||> Walters Chambers and Associates Ltd.
||> Structural Engineering Consultants
||> Suite 1330, 10130 - 103 Street
||> Edmonton, AB  T5J 3N9
||> phone:  (780) 428 - 1740 Ext. 5111
||> direct:   (780) 917 - 5111
||> fax:       (780) 423 - 3735
||> email:    wayne.stewart(--nospam--at)walterschambers.com
||>
||
||

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