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The ends are secured, so how much load can a 6' span of SPF 2x4 support when turned on 3.5"?

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Your caps lock button appears to have malfunctioned. You might want to commence reparations on that. –  ratchet freak Apr 2 '12 at 20:13
    
It depends on the loading distribution. Point loading? Evenly distributed across the span? –  Doresoom Apr 2 '12 at 21:30
    
Also, the modulus of rupture varies widely both with wood species and moisture content. –  Doresoom Apr 2 '12 at 21:41
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3 Answers 3

Check out this site : http://www.msrlumber.org or http://www.msrlumber.org/spantables.pdf it has all the answers to spans for most applications. There are several good sites that have tables, just google "lumber strengths".

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The PDF proves to be a vital source of information. Very nice –  ppumkin Apr 3 '12 at 10:49
    
Many years ago, we won't say when..... I had to study strength of materials charts in architecture class. With all the new LAMS, beams and trusses, the charts are more important than ever. –  shirlock homes Apr 3 '12 at 20:15
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The Sagulator says it will support about 375 pounds (evenly distributed) before there is noticeable deflection. I recommend you go to the site, read the notes, and play around with the numbers yourself.

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Note that while this is a good resource, it won't tell you when the beam will actually break. Try replacing 375 lbs total with 90000 lbs/ft. The calculator gives a sag of nearly 29" per foot, which is obviously impossible. –  Doresoom Apr 3 '12 at 17:16
    
Good point. The "Sagulator" is really geared more toward shelving, whereas the span tables that shirlock referenced are geared more toward structural engineering. It's not entirely clear from the question what the OP's intent is here. –  mwolfe02 Apr 3 '12 at 19:16
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The American Wood Council offers just the tool you need at http://www.awc.org/calculators/span/calc/timbercalcstyle.asp Maximum Span Calculator for Wood Joists & Rafters/ You'll want 'live load', meaning people (and/or stray deer).

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