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Re: Analyzing Existing Joists for Snow Drifts....

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> From: "Daniel Boltz" <dboltz(--nospam--at)1st.net>
> To: <seaint(--nospam--at)seaint.org>
> Subject: Analyzing Existing Joists for Snow Drifts....
> 
> An architect is adding an addition to a school that will cause snow drifts

> These are both less than the allowable loads.  My problem is that I cannot
> determine if the snow drift is causing a shear reversal due to the point

> insignificant.  My question is, how much distanc! e off of the original
> zero shear location is considered "insignificant"?

I assume that you are concerned about a force reversal to compression in
the OWSJ web member. This is not necessarily bad. Magnitude is the real
issue.

Your first ballpark estimate would be to consider how far from centre
the zero shear has moved in relative terms. That will give you a good
feel for the possiblility of detrimental web load reversal effects (e.g.
6"/(40'/2) = 0.025, 2.5%). Looks trivial to me.

Secondly, how far is that with respect to the chord panel points?
Typically, there will not be any gravity load related difference in web
load direction if the new zero shear is within the same "panel".
 
> utilized.  I'm kind of at a loss for the Metal Building as 1, they usually
> have terrible lateral drift limitations which the addition's expansion
> joint is not currently accommodating, 2, the foundation construction is
> unknown, and 3, the original manufacturer is out of business and the
> school has no existing drawings for the frame.  Short of field measuring
> the frames and purlins and reanalyzing the structure, I don't know of a
> good, safe route to reinforce the existing frames.

Without good background data on the structure and foundations, there is
little about such a renovation to which I would put my seal. You should
also consider some material tests.

-- 
R. Paul Ransom, P. Eng.
Civil/Structural/Project/International
Burlington, Ontario, Canada
<mailto:ado26(--nospam--at)hwcn.org> <http://www.hwcn.org/~ad026/civil.html>

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