Redwood beam bending stress

[m1208]

I have an exterior second story wood deck and need to replace the existing 6x12 (22' long) wood beam. I like to use redwood beam to prevent dry rot issues. The only available beam type in our area is 6x12 redwood, con-heart grade. For design, I need the allowable bending stress for the 6x12 redwood beam. The Codes (i.e. NDS and UBC) do not have the bending stress listed for members thicker than 4" (see attachment). Any idea where I can get allowable bending stress for 6x12 redwood beam. If nothing is listed then I have to use glued-laminated beam, and in that case, how do I make sure that the beam is rated for weather exposed area?
Thanks

 

[jdgengineer]

Why not use a pressure treated beam? Or if that doesn't calc you would likely want an Alaskan cedar glulam for exterior rating or you could use a wolmanized PSL (Weyerhauser) or treated LVL (Pacific Woodtech)

 

[m1208]

I could not find 6x12 pressure treated in our area. Are there any listed bending stress values for pressure treated beam of 6x12? If we use glulam, how do we make sure that is for exterior use, subject to rain, when they deliver it to the job site?

 

[jhnblgr]

I don’t think you’re going to get a 6x12 wood beam to pass at that span. https://www.fpl.fs.usda.gov/documnts/fplgtr/fpl_gtr190.pdf

 

[XR250]

I don’t think you’re going to get a 6x12 wood beam to pass at that span. https://www.fpl.fs.usda.gov/documnts/fplgtr/fpl_gtr190.pdf

yup, I imagine it will have significant deflection issues.

 

[phamENG]

NDS Supplement lists Redwood in Table 4D, Reference Design Values for Visually Graded Timbers (5"x5" and larger). There's a section in the table for "Beams and Stringers." But you can also check with the supplier to see under what rules the timber was graded and go to them for design values. It will also let you verify that it has actually been graded, which is important.

But yeah...don't just check stresses. Do a complete design. Deflection is going to be a serious issue with this. Unless the deck's only 4' deep. If it's carrying 2' of trib it might pass...maybe...