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# Redundancy Factor

• To: seismo-all(--nospam--at)seaint.org
• Subject: Redundancy Factor
• From: "Ron O. Hamburger" <ROH(--nospam--at)eqe.com>
• Date: Fri, 30 Jul 1999 14:45:57 -0700
• Cc: seaint(--nospam--at)seaint.org

```
A recent thread of discussion on the list server has called my attention to
what I believe is an uintentional and also unfortunate problem with this
factor in the 97 UBC.

When the committee first developed this factor, the intent  was that the
rmax represent the % of the story shear carried by the most heavily loaded
element.  We then proceeded to define what an "element" is.  For example,
each brace is an element, etc.  When we got to shear wall structures, the
intent was that each individual wall pier across a horizontal plane cut
through the building would be an "element".  Then, someone on the committee
noted that if you had a 100' x 100' tltup type structure, with a number of
20' wide panels, this would be considered to have high redudance (because
each 20' panel would be an element) however, if you had the same structure
with cast-in-place walls, then it would be non-redundant, as the whole side
of the strucure would be only one element.  In order to solve this problem,
for shear walls, we introduced the rule that when a shear wall exceeded 10'
in length, each 10; segement (or part thereof) could be considered an
element.  The intent was as follows  - If you have a wall line with 10 - 4'
piers between windows, each pier would be an element.  If you had a wall
line with a 40' wall, you would have 4 elements.

Somehow, in the word smithing that went into the actual code language, this
logic got badly messed up.  Now each wall segement is multiplied by 10/lw.
This has the desired effect for long walls, but has a penalty effect for
short wall segments.  This was, in my opinion, never intended.
This has some serious negative impacts on wood frame construction.