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RE: Historic Wood Structure; How to Dete

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Let me just say to all who contributed...thanks a great deal......

Sound engineering judgement is always improved when you hear what some
colleagues have to say on the topic....

If any of you are interested, I do have an article from Bob Falk, Forest
Product Labs on the reclamation / reuse of old timber and the strength
degradation.....

I have decided to have a definitive double check on the species
type......have a "grader" from NELMA look at the insitu lumber, then
make a decision on what allowable I will use........I have been told by
the grading agency that he should be able to definitely tell me what it
is "not"....and since I only have three grades available in oak...that
will help immensely.....then I'll choose and go from there.....

Again, thanks to all for the input.....

Robert

-----Original Message-----
From: Roger Turk [mailto:73527.1356(--nospam--at)compuserve.com] 
Sent: Friday, April 25, 2003 2:58 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: Historic Wood Structure; How to Dete


Robert Rogers wrote:

. > I always thought grade & species were equally important with regard
to . > member strength....just the allowable bending stress on a Mixed
Oak can . > range from 725 psi (for a No. 2) to 1350 psi (Select
Structural) per the . > 1997 NDS supplement.....and I'm still a little
confuse.......if I just . > assume this value, what is my engineering
basis for this assumption ?

. > I do like the idea regarding the increment borer.....and no, they
did . > not use one.....they mainly "looked" and "tapped" and did some
drilling . > with 1/8" bit & a portable drill....

First, let me say that a trip to the University library is in store for
me 
this weekend to research ASTM standards on the full-size, in-grade
testing of 
structural lumber.  Hence, what I say here is based on the previous
testing 
program of small, clear wood specimens.

Testing of species was performed on small, 2" X 2" clear wood specimens.

Grades were determined based on their "bending strength ratio," thus,
for 
structural joists and planks (WWPA Grading Rules, 1981):

   Bending strength ratio     Grade
      65%                     Select Structural
      55%                     No. 1
      45%                     No. 2
      26%                     No. 3

Strength reducing characteristics for members were limited to those that

supposedly would not affect the bending strength ratio below these 
percentages.  (Examples of calculating these effects are included in
ASTM 
D245.)  Therefore, it is/was the basic strength of the species which 
determined the allowable stress in the various grades that caused me to
say 
that species is more important than grade.

The UCBC is an ICBO (west coast) document that says DF No. 1 stresses
can be 
used to evaluate existing wood structures.  It does not really address
east 
coast hardwood construction.  Since the species is identified, I would 
use the allowable stresses for the species, not DF.  Since "mixed oak"
is 
graded under the grading rules of NELMA, I would get a copy of their
grading 
rule book, first, to see if there are members which would be below No. 1

grade, and, second, to see if in-place grading would be necessary.
NELMA 
should also be able to provide a list of qualified visual graders.

Barry Welliver wrote:

. > The recommendation is to use the original allowable design values
under 
. > the code in effect at the time of construction.

Yes, the UCBC does state that you can use the original allowable design 
values, but, *only if:*

   The load has not increased, *or,*
   The occupancy has not changed, *or,*
   Failure of a member has not occurred.

Otherwise, you have to use the current allowable design values.  In
Robert 
Rogers' project, failure has occurred, e.g., shoring has been installed.

Structural failure:  When a structural member cannot support the loads
or 
function as originally intended.

Roger Turk

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