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RE: A question about evaluating an existing wood structure

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2x8, 16" oc.  You have a lot of horsepower for a 13'-6" max span.  What is your
roof slope?  The cheap seats might consider all present loads applicable to your
design and back calculate the required fb and E to meet demands.  Perhaps you
will have the luxury of recognizing that the worst lumber available would
service demand forces.





William Keil <WJK(--nospam--at)brph.com> on 10/18/99 12:52:09 PM

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 Subject: RE: A question about evaluating an existing wood    
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Scott,
By taking a core sample and submitting it to a lab, they can determine the
species and other things to help zero in on an allowable stress.  I cannot
remember the name of the lab we submitted the sample to ... too long ago.  I
would suggest contacting NFPA in Washington, DC, for lab information.
Performing the test will be beneficial because odds are the roof will not be
able to take any more load if you make conservative assumptions - been
there, done that.

William J. Keil, P.E.


-----Original Message-----
From: Scott Maxwell [mailto:smaxwell(--nospam--at)engin.umich.edu]
Sent: Monday, October 18, 1999 3:41 PM
To: seaint(--nospam--at)seaint.org
Subject: A question about evaluating an existing wood structure


I am going to show my ignorance in wood construction, but...

We have an existing wood structure that the architect wants to change the
roofing on.  We need to evaluate the existing wood members for the new
loading.  The roof framing is 2x8 @ 16 oc with the longest span of about
13'-6".  The existing drawings don't specify the wood grade or species.  So
the questions is how would go about "selecting" an allowable stress?  Would
you try to "back calculate" what the wood species and grade should be based
upon "existing" loads?  Do material testing to try and determine wood
species and grade...and if yes, what testing would that be?  I am guessing
that this framing was not orginially "engineered".  Any suggestions or
input would be greatly appreciated.

Thanks much,

Scott