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RE: Field Grading of Existing Wood Framing

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David,

Your reply is consistant with some other sources I have reviewed. I have
heard of engineers using the allowables from the code they were approverd
under if the lumber was stamped, but that was a while ago. Old lumber is not
necessarily stronger than new lumber of the same grade. As I understand it,
the old grading procedures did not take into account the degree of
imperfections in lumber used in real conditions, they tested smaller less
representative sticks. It makes me wonder how many buildings there are out
there that may be subjected to failed members. I have been looking for a
code section or document that states that current NDS values need to be used
for old lumber, do you know where this is?

Thanks for your reply,

Jeff


-----Original Message-----
From: Gaines, David [mailto:David.Gaines(--nospam--at)hdrinc.com] 
Sent: Thursday, April 17, 2008 3:53 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: Field Grading of Existing Wood Framing

Jeff,

If the joists have split at the knots, repair them by sistering on new LVL
or PSL beams on both sides. Shore up the damaged purlin before you attach
the new wood. If there are other purlins with  weak points that are
susceptible to cracking or failure, recommend that they be repaired by the
same means as well. It's a lot cheaper to repair them before they crack. The
new lumber can be bolted on to the 4x112 purlins below the
2x4 or 2x6 subpurlins.

Recommend to inspect as much of the roof as you can get to and itemize the
areas you can not inspect. You only need to upgrade the purlins and beams
you are adding loads to or remodeling in. Write a careful Scope of work
outlining what you're offering to do and what you're not covering.

By re-grading the existing lumber you are not likely to improve on a Select
Structural grade (nothing better than SS) and the allowable lumber stress
values for any grade will be lower today than what they were in 1977.

If they're adding TI loads to the original, 1977 beams you need to evaluate
them by the current code, not the 1977 code. Current lumber grading values
have been revised to lower values and so most of the purlins you check will
not work with the original loads, much less additional loading. You'll need
to reinforce the structure anywhere they modify, remodel or add loads. Check
your beams and girders in areas that may be affected by added loads too.


Dave Gaines, P.E.

Structural Project Engineer
HDR ONE COMPANY | Many Solutions
251 S. Lake Ave, Suite 1000
Pasadena, CA 91101
T: 626.584.4960
F: 626.584.1750
email: david.gaines(--nospam--at)hdrinc.com 


-----Original Message-----
From: Jeff Smith [mailto:jeffsmith7(--nospam--at)comcast.net]
Sent: Thursday, April 17, 2008 3:10 PM
To: seaint(--nospam--at)seaint.org
Subject: Field Grading of Existing Wood Framing

I am looking at a 70's office building that has 2 cracked 4x roof purlins
out of maybe 300. There is a knot in the tension zone and looking around the
building there are several other beams that also have knots in the tension
zone. It is stamped Sel Str. The tenant improvements will add some
additional load to the beams. Based on an analysis using allowables from the
1977 UBC these beams are adequate. Do you think hiring a grader would be a
good idea and once graded would it be appropriate to use the design values
from the 1977 UBC, can a grader make that decision?

Thanks,

Jeff

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