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RE: Wood shrinkage

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We have done a lot of four story wood framed buildings, and never had a
call back for a shrinkage related problem.  The top and bottom plates
are where all of the shrinkage will occur.  I would not recommend using
2x floor framing, as this will add considerably to the shrinkage.
I-joists, LSL rim boards, and pre-engineered floor trusses have
significantly less shrinkage than say a 2x10.  When you calculate the
actual shrinkage of the plates, you should find that it is an
insignificant amount of shrinkage (on the order of maybe a 1/4" to
3/8").  Of course you have to use KD-19 or KD-15 wood, not green lumber.


Charles F. Espenlaub, III, P.E.
Martin-Espenlaub Engineering



-----Original Message-----
From: JPRiley485(--nospam--at)aol.com [mailto:JPRiley485(--nospam--at)aol.com]
Sent: Friday, February 25, 2000 4:39 PM
To: seaint(--nospam--at)seaint.org
Subject: Wood shrinkage


Architect wants to build residential structure in Iowa.

     4 stories (1 at grade, 3 supported)
     Wood stud bearing walls
     Approx. 15,000 sf per floor

Fire safety issues have been hashed out between the architect and the 
building official.  The building official required the architect to hire
a 
structural engineer on this project "because it is 4 stories."  For an 
essentially identical 3-story building, he was allowed to do the
engineering 
himself.

My concern is with the following UBC section:

SECTION 2308  -  WALL FRAMING
Wood stud walls and bearing partitions shall not support more than two
floors 
and a roof unless an analysis satisfactory to the building official
shows 
that shrinkage of the wood framing will not have adverse effects on the 
structure or any plumbing, electrical or mechanical systems, or other 
equipment installed therein due to excessive shrinkage or differential 
movements caused by shrinkage.  The analysis shall also show that the
roof 
drainage system and the foregoing systems or equipment will not be
adversely 
affected or, as an alternate, such systems shall be designed to
accommodate 
the differential shrinkage or movements.

It's probably within the architect's overall responsibility to
coordinate the 
building materials so that we don't buckle a plumbing pipe, or something
like 
that.  And hopefully, the "analysis" of the effects of shrinkage will
not 
entail much more than a shrinkage estimate (by me) and an evaluation of
its 
effects on the various systems (by someone other than me).  Seem
reasonable?

Estimating shrinkage:  I believe longitudinal shrinkage in
Doug-Fir/Larch(N) 
is negligible, possibly 0.1%.  The significant shrinkage occurs in the
stud 
wall plates and rim board.  In the Timber Construction Manual there is a

formula for estimating shrinkage based on initial and final moisture
content. 
 And I found this shrinkage calculator on the Internet:  
http://www.woodbin.com/calcs/shrinkulator.htm    It boils down to 
establishing initial and final moisture content . . . help.

John P. Riley
Riley Engineering
Blue Grass, Iowa