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Re: Collar Ties

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Lynn, first let me thank you for faxing the analysis and sketch to me. As you had suspected, the pitch of the roof made the deflection at the walls too much. Even going to a 4x member with collar ties on both sides did not help too much.

Solution:
I contacted the company designing the roof trusses for the rest of the structure. We came up with a sissor truss design that conforms to my dimensional constraints. Since there is a bottom chord to take the tension load, the calculated deflection at bearing was only 1/2" for dead load and 1/3" for live load. Since live load will most likely never be realized here in the desert, I have discussed with the contractor to set the walls at a 1/2" deflection inward to anticipate the 1/2" loaded deflection.
This seems like the least costly solution to the problem and still allows the architect the inside vaulted depth he needs for the metal ceiling arch.
If he needs more, he is willing to raise the pitch. BTW the exterior pitch is 6:12 as I mentioned and the interior pitch is 4:12. The truss is 2x4 top and bottom chords with plated connectors and a "collar tie" with some diagonal and vertical struts.
I'm posting this letter on the net so that others can read the solution who have been following the post.
Thanks again for your help,
Dennis


Dennis S. Wish PE
wish(--nospam--at)cyberg8t.com

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on the lips of all children"
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