Stresses in wood

[murungu]

I am having to check the strength of a mezzanine floor built of 2x8 beams, 3/4 ply and 2x4 posts.

Does anyone have tensile stress etc info for spruce and pine?
Is there a standard floor load or Safety factor I should aim at?

Makes a change from the usual financial engineering I am cursed to.

Cheers

 

[jheidt2543]

A few thoughts:

1. You should check the members for grading stamps, that would confirm what stresses you can use.

2. You can call your local lumber yard and ask them what the "normal" lumber grade and species that is sold for general construction. However, this is subject to change quite often depending on the lumber market. But, it is a place to start.

3. If you don't see any grading stamps, then you don't know for sure what the wood grade of the framing is. I would consider the wood as Standard Construction Grade.

4. From the AITC Timber Construction Manual, 2nd Edition Southern Pine, 2" to 4" thick, 6" and wider, Grade No. 3 Fb = 825 psi, Fv = 75 psi, Fc = 345 psi and E = 1,400,000 psi.

5. The stress ratings of lumber have changed some, so for more accurate numbers you could check the website for the Southern Pine Council.

Hope this helps!

 

[ERV]

In addition to jheidt2543 post,

Mezzanine floors for commercial should be engineered to 100 psf live load (in addition to 15 psf dead load). For residential it is 40 psf live load except balconies(balconies in residential is 60 psf).

 

[JAE]

ERV - please clarify the 100 psf live load - in the U.S. the live load is based on occupancy so a mezzanine used for office space would have a live load of 50 psf (with 20 psf more for partitions) and a mezzanine used for light storage would be 125 psf.

100 psf is for public assembly, exits, etc.

 

[ERV]

I assumed it was a mezzanine for public assembly, sorry, but none specified. Office space may also have 100 psf for file cabinet area (I have run into this recently).