# 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: "Sprague, Harold O." <SpragueHO(--nospam--at)bv.com>
• Date: Thu, 25 May 2000 10:47:36 -0500
```Wayne,

The Z factor as used in the UBC is the seismic zone factor.  It is used as a
means to determine the "Seismic Coefficients" Ca and Cv (Re: 1997 UBC, Table
16Q and 16-R).  It is expressed as a fraction of gravity.  If you would like
a more in depth discussion of Z, reference Recommended Lateral Force
Requirements and Commentary, (AKA the Blue Book) by SEAOC.

Be careful not to use the Z factor as an indication of predicted earthquake
ground accelerations.

Regards,
Harold Sprague

> -----Original Message-----
> From:	seaint-return(--nospam--at)seaint.org [SMTP:seaint-return(--nospam--at)seaint.org]
> Sent:	Wednesday, May 24, 2000 12:46 PM
> 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.
>
> 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
> <mailto:wayne.stewart(--nospam--at)walterschambers.com>
>

```