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Re: Question for East Coast Engineers

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Richard_Ranous/OES(--nospam--at)oes.ca.gov wrote:

>  Maybe Kelly Cobeen or Bob Bossi can provide us an
> update?

  The conventional construction provisions of the 1994 and 1997 UBC are
substantially different than the 1991 edition.  Until 1994 the only
limitation was "unusual size and shape",  terms that were undefined.  Kelly
Cobeen, Ed Zacher and I were members of the Conventional Construction Task
Force that developed the current provisions.  That task force included
designers, contractors, the wood industry and building officials.  The
purpose of this effort was two fold:
1.    to provide uniformity in the application of the conventional
construction provisions; and
2.    to address the changes in architecture that occurred since  the post
W.W.II FHA "tract box" style of house had given way to more complex "modern"
architecture.

The code change did several things.  It limited the use of conventional
construction to only certain occupancies and certain maximum load limits.
Prior to 1994 there were no such limits.  It also defined what "unusual
shape" meant using code defined irregularities.  Unusual shape became moot
once maximum braced wall line spacing was developed.  Very little changed in
the actual provisions except for a few connection nailing improvements.  For
further detail see the September-October 1996 Edition of Building Standards
Magazine.

The issue of no requirement of connecting interior braced wall lines to the
roof diaphragm was an initial oversight that was to be corrected by a
further code change but ICBO suspended code development for the UBC before
the change could be processed .

Overall I believe that the current UBC (and future NEHRP and IBC)
conventional construction provisions are a significant improvement over
those before 1994.  Regardless of what calculations might show, well built
and maintained conventionally constructed buildings even from the early
1900's, before codes, performed well as long as cripple walls were braced
and the building was anchored to the foundation.  Remember also that prior
to the 1970's few, if any, wood frame buildings were "engineered".  My
experience in evaluating "failures" is that  they can much more
appropriately be attributed to poor construction practices and deterioration
than the design methodology used.  In fact, I found after the Loma Prieta
earthquake that newer engineered structures often performed worse than older
undersigned structures of the same type.  I believe that this was primarily
because the engineered structures used fewer, stronger (but not necessarily
stiffer) and more highly loaded lateral force resisting elements.  Many of
these elements were plywood behind stucco and were found to be totally
deteriorated due to moisture infiltration and decay.

The question of the need to "engineer" all buildings cannot be addressed by
the code.  In California it is the Engineer's (and Architect's) Act that
governs (Cal B&P Code 6737.1).  Any residential wood frame building of four
or less units that conforms to the conventional construction provisions is
exempt from professional design and, even then, only those elements that
deviate from the conventional construction provisions need be "engineered".
It would take an act of the state legislature to change that and I think we
can all predict the outcome of such a bill.

If any one feels that the IBC conventional construction provisions need
further change, there is still time to submit challenges to the next
(final?) draft of the 2000 IBC.