Re: pipe trusses

Posted by RodInNS on December 30, 2005 at 10:06:02 from (142.177.72.6):

In Reply to: pipe trusses posted by Comfortking on December 29, 2005 at 19:42:07:

Hmmmm. I'm sure there's probably a point at which you could install enough pipe to make this safe, but I'd be uncomfortable with what you're describing. That seems like a lot of unsupported span for a rafter. If you were talking about a structural webbed truss, that would be one thing. Why not trade some pipe for .... 10" "I" beam, and then use the pipe for posts. Pipe works well where the member is in linear compression. It will bear a tremendous amount of weight standing on end. I would also put a row of posts along the other wall to carry the shed roof rather than attach to the existing building. You're dealing with a massive amount of weight there to support entirely off another wall.
You need to remember that pipe is simply not a structure that is made to carry weight horizontally. An I beam will allow far more load carrying capacity with far less weight. Just think for a minute about a length of steel flat bar.... say 1/8" thick by 4" wide. If you lay that strip on the floor, you can bend that length in a circle by hand. Now, turn that length on edge, and then try to bend it like that. There, you have the benifit of 4" thick steel in load bearing ability. Steel buildings rely a lot more on "engineering" to gain strength than simply a brute amount of material.
The other consideration I would have in using that pipe for a rafter would be the strength of the joint on the post.... I think it would be difficult to make a joint strong enough to carry the weight. All in all, I'm sure you could make this work...... but the point of the first reply was that the strength to weight ratio for pipe in this application is poor...... although there is probably a point where it would be safe. I just wouldn't want to guestimate where that point is at. FWIW,

Rod

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