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RE: structures & ethics

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Bill,
You reminded me of one other point. There is a Live load reduction based on
tributary area exceeding 200 square feet on any roof member. Don't forget to
look at this in your analysis.
Dennis

-----Original Message-----
From: BCainse(--nospam--at)aol.com [mailto:BCainse(--nospam--at)aol.com] 
Sent: Monday, November 22, 2004 1:33 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: structures & ethics 

Steve-
I would recommend:

1. Check with the building department and/or building owner to see if
original plans are available.  Sometimes, substantial changes have been made
over time which could effect the loadings.  

2. Get a quick peer review from the list on your purlin calculations by
posting a more complete description of the materials supported and your
estimated loads and the sizes of purlins and the material properties you
assumed(the information you posted is pretty sketchy for the purlins). The
calculation is very straightforward and takes only minutes.  From the glulam
size, cantilever and common bending strengths available in the 1970's, it
appears you may have a dead load of about 19 psf if they were designed to
the limit. If so, that would require some rather hefty purlins.  Also, have
you attempted to visually determine the approximate grade of the purlins?

2. If the condition is as bad as you indicate, sit down with the client and
explain what you found and the potential consequences (wood can let go over
time either in a brittle manner or by cracking and sagging [that is why the
NDS specifies a Cd factor for loading duration}). The former is definitely a
life safety issue.

3. If you judge that, in your professional opinion, the structure is a life
safety problem, you need to consult with the local building official.
Somehow I can just hear the opposing attorney asking, "You knew it was going
to fall down and you didn't do anything?"

HTH,
Bill Cain, SE
Berkeley CA



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