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rpineo 08-06-2010 07:48 AM

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Originally Posted by Nestor_Kelebay View Post

Don't you remember doing that?
What I remember most about sizing and design calculations was that we would utilize a set of assumptions in order to reduce our "problem" to a nice, neat theoretical approximation. Then we would labor to produce pages and pages of meticulous, painstaking mathematics. We would then compare the results of these seemingly endless equations against some tables to determine the size of beam or plate or cable(s) that we would need.

And then we would multiply that requirement by a factor of 2 or 3 for "safety", because ultimately, nobody really knew if all the theory would actually work in practice!

But that aside...

If I read your post correctly, you are discussing the sizing math around the following configuration:

(1) Start with existing beam (joist). Assume a 2x10 wooden joist.
(2) Attach a second 2x? member (lets say a 2x6) along the bottom edge. This theoretically results in a 2x16 compound joist.
(3) Secure the beams together using mending plate(s) - as shown in attached sketch, where 'x' chars are mending plate(s).

My original post was meant to illustrate my uncertainty about how closely this practical application would match the theoretical effectiveness. I admit that it has been some time since I have had to do such math, so my misgivings are based mainly on gut feeling. Also, the notion of sistering joists has been around for a long, long time. So has physics. If "sistering" in this fashion was the superior approach, then one is left to wonder why nobody has been doing it this way. Is there some major practical drawback, or is Nestor really onto something here?

If the latter, you might want to consider a patent!

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