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Re: Wood structure with wood diaprhagm - question on disconntinuity

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In a message dated 9/30/1999 5:19:16 PM Pacific Daylight Time, Seaintonln 

<< One questions, what would be the difference in the chord design if the 
roof had been simply flat. Isn't it the same as the maximum moment divided by 
the depth of the diaphragm (net) - or is there additional deflection expected 
due to a discontinuity that might exist at the junction of the two roofs? >>


In practical terms, there wouldn't be a difference. you would calculate the 
chord forces the usual way. However, you need to have a continuous chord 
(blocking & strap or a continuous member at the top plate line of the flat 
roof within the wall of the sloped roof, all the way to the end. Just don't 
let the shape of the roof scare you as long as you follow your "principal of 
mechanics" instinct.

You can also experiment with the model I described in my earlier post by 
adding chord members and see the stiffness the provide. The trick is that the 
stepped roof will try to balance itself under the lateral load into a flat 
shape. To prevent this you need to provide an alternate path (i.e., a chord 
at the flat roof level) all the way to the end of the sloping roof.


Oshin Tosounian, S.E.