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Re: Re: Timber pitched roof as a Diaphragm

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Subject: Re: Re: Timber pitched roof as a Diaphragm


>seaoc(--nospam--at)seaoc.org,Internet writes:
>>I am not aware of any software for this application.  my personal opinion
is that diapragms do not really work for pitches over 6:12 unless you prvide
a line of bracing close to the ridge line.  my 2 cents worth.
>>
>>Tarek Mokhtar
>>consulting engineer
>
> >Thanks for the response Tarek.  I am of similar opinion and I normally
specify a diaphragm or braced connection at or near the ridge line.  The
problem becomes difficult where the ceiling is to be vaulted.  As a further
analytical tool for large roofs what do you think of using analyses like
that used for steel deck design?  Or using thin shell analyses?
>
>
>I can't quite picture what you are discussing here.  Are you stating that a
roof with a pitch over 6:12 will not behave as a diaphragm unless there is a
special connection at the ridge?  What is a braced connection at the ridge?
How does a vaulted ceiling come into play?  Without seeing sketches I find
it hard to follow what is being discussed.
>
>Thanks for taking the time to explain this further.
>Richard Lewis, P.E.
>Missionary TECH Team
>rlewis(--nospam--at)techteam.org

I have posed the problem of rationalizing the use of a pitched roof for
diaphragm action (lateral loading aligned and in plane with the roof
surface) when there is no diaphragm, or bracing, action at ceiling level
between associated shear walls.  This occurs when the ceiling is vaulted.
>From the analogy of a piece of folded paper or card you can see that
diaphragm action is possible, however, I suggest that the steeper the roof
pitch the more critical becomes the ridge connection rigidity.  Similarly
the greater the pitch and the larger the roof the more it acts like a thin
shell (?).  I also suggest that for pitched roofs the gable ends can also
act as vertical stiffeners or diaphragms.


I had, furthermore, queried if anyone has addressed this problem and/or if
there was software available that did so.

Thor Tandy P.Eng
Victoria  BC
vicpeng(--nospam--at)vtcg.com