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"Ron O. Hamburger" <ROH(--nospam--at)>
Date: Fri, 30 Jul 1999 14:45:57 -0700
Subject: Redundancy Factor

Previously had written:

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 structure 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

Please consider this matter, at your next Seismology Committee meeting.