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RE: Field Grading of Existing Wood Framing

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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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