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# RE: Rigid frame deflections (again)

• To: seaoc(--nospam--at)seaoc.org
• Subject: RE: Rigid frame deflections (again)
• From: "Powers, Tony" <tpowers(--nospam--at)hdrinc.com>
• Date: Thu, 22 Jan 1998 16:37:03 -0600

```It's not clear to me if you are still looking for further clarification,
but just in case, I'll address this post:

As you mentioned in your previos post, for shear walls the one with the
lower height to length (H/L) ratio will be stiffer.  However, for the
rigid frame, the overall stiffness is proportional to the stiffnesses of
the  individual members, not the overall length to height ratio.  So if
the column properties are all identical , as in your example, then the
overall frame stiffness would be dependant only on the stiffness of the
beam, and the shorter beam would be stiffer.  Therefore, the frame with
the greater H/L ratio would be stiffer.

If in your example, you kept the beam properties constant and varied the
height of the columns (all other properties being constant) then the one
with the shortest columns (hence, the stiffest columns) and thus the
lowest H/L would be the stiffest.  The conclusion, therefore, is that
there is no simple relationship between H/L and lateral stiffness for
rigid frames, unlike the case for shear walls.

Hope this helps,

Tony Powers

P.S. Since I started this response, I've received your latest post which
indicates you've figred it out and another from (I can't remember who?)
so this may be a bit redundant.  If so, hey, delete it.

> The column heights and cross sections are all the same. It was the
> beam
> that was longer. It seems to me that a lateral force-resisting element
> that
> has a longer span in relation to its height should be stiffer that one
> which has a shorter span to height ratio. That was where I was coming
> from
>
> Kate O'Brien
>
>

```