Foot bridge truss(es) from green cedar
Greetings –
I’m having a large western red cedar taken down next week. The tree service guy suggested I have them cut it into logs that will fit on my 14′ car trailer and run it up to a small custom mill nearby and have it milled into lumber. Good idea, I thought but what to do with it?!
OK, I’ve got a small stream running in a gulley in front of the house. I says to myself, “Self, here’s the lumber for your bridge”.
I don’t have any problem designing a trussed structure, the question is in regard to how well suited the cedar “off the saw” would be for the project. The rule of thumb is 1 year per inch of thickness for air drying most hardwoods, but cedar is hardly a hardwood. I plan on having the log(s) milled to 2″ x 6″ (full dimensions) lumber and building the trusses out of these. I’m hoping, also, that there will be sufficient full heartwood lumber out of the logs so I won’t be using any sapwood.
Also, I don’t have access to any design criteria for through bolted connections with cedar. I’ll be using 1/8″ gusset plates for the truss member connections which I may fabricate myself unless I can find some suitable Simpson framing hardware. Does anyone have suggestions on min. edge distances for bolted connections and/or end distances for same?
From Beautiful Skagit Co. Wa.
Dennis
Replies
Here's some strength/span data for cedar including green:
http://www.wrcla.org/cedarspecs/designershandbook/engineeringdata.asp
The awful thing is that beauty is mysterious as well as terrible. God and the devil are fighting there, and the battlefield is the heart of man.
- Fyodor Dostoyevski
Dennis,
Cedar being so soft, you ought to look into split rings to transfer the shear at your bolted connections. Check out the Forest Products Handbook, or run a Google search. You can use them with meatier timbers than the 2 x 6's you are considering. The bolt clamps the joint and the split ring transfers the shearing loads between members. A simple and elegant system, often used on old bridges made from timber.
Bill
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Edited 6/2/2005 2:19 am ET by ELoewen