I hope I did not mentioned anywhere
that the building is, or was supposed to, "come tumbling down." I do not
believe in that happening. The building survived at least two
good-size earthquakes (1971 and 1994), and is not going anywhere any time
soon. After all, the safety factors in wood design are in the
order of 4-to-6, which, obvioulsy, quite safely covers the noted overstress.
My problem is - can we allow the
building to stand without strengthening, even in the "repaired to preexisting"
condition, while knowing that it is not code-compliant?
Example: based upon my observation, I
would assume that the building had not been re-roofed. What
will happen when the reroofing start? Probably, nothing. But at a
12' height, something may happen. Then what?
I do not really care what my client
would THINK about my degree. I do care about what he will be willing to DO
about my license in case of any problem - no matter how much he wants to
save money now.
Along with my professional and
personal ethical considerations, this is my main concern.
V. Steve Gordin, PhD
----- Original Message -----
Sent: Monday, November 22, 2004 10:58
Subject: Re: structures &
Since the building has been standing up for the
last thirty years in
spite of the 70-100% overstress for DL +LL and
15% for DL, I would
guess it will stand another 30 years
without any problem (you did not
say that the members were sagging &
assumming no major earthquak hits
it). Either the loading is
being overestimated or the strength
Even though the
code requires a Live Load on the roof members, the
seldom see that load - that could explain the high
overstress for DL+LL
combinations without any detrimental effects to the
(Some time ago, there was a discussion in this forum
about metal connectors
in modern day pre-manufactured wood trusses that
failed when subjected to
full design dead + live load.)
The factor of safety probably explains
the 15% overstress for DL
without any detrimental effect.
tell your client that he has to replace the undamaged roof
your calc shows that they are highly overstressed and
should have come
tumbling down 30 years long ago, he will wonder if you
did earn your PhD
the old fashioned way. I think you should tell your
client what you
found based on your calc and let him make the decision.
clarlify the scope of work in your contract and limited to
work with the assumption that the existing framing is adequate
based on the
fact that it is still standing. After all, gravity is
11/22/2004 9:40:06 AM >>>
I was asked to
provide repair plans and specifications for an existing
roof damaged by a
vehicle (sic). The problem now became not only
The building is apparently a former
post office (1970s?), with 5 1/8"x
24-3/8"glulam beams @26' o.c.
cantilevering 16' off brick wall along one
side. Further into
the building, the glulams also bear on wood
columns, and then cantilever
and support other glulams spanning toward
the opposite brick
Sawn purlins span about 26' between the glulams at 8-to-9
on-center, supporting 2x4 @24", some insulation, lots of
conduits and ducts, plywood diaphragm, and the composition
The "fascia" (still 6x12, nominal/typical) purlin of the
apparently hit and broken by the u-turning big rig, with
damage (delamination with lateral offset) to one of the
I ran the analysis
based upon the current codes as well as upon the
1960s and 1970s codes
(UBC). The analysis shows that the undamaged
glulams, and columns are inadequate against DL+LL
overstressed), and even against DL only (with 0.9 factor,
For the sawn lumber, I tried even select structural (dense
structural) - did not help...
Some of the purlins are visibly
sagging. The glulams look OK.
I can just replace the damaged
purlin (these are the only ones that are
due to 50% tributary
area) and to repair only the damaged glulam to the
(I can do it with lag screws etc.). After all,
the building may be OK
solely by the fact of it existing like that for
about 30 years, right?
If I am right in my assumptions - how that could
happen (don't answer
If I am wrong in my assumptions - what
am I missing?
What should I do within the limitations of common sense,
analysis, and professional ethics?
V. Steve Gordin, PhD
Registered Structural Engineer
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