exterior deck, beam design

[rnorth]

I am designing a beam for an elevated exterior deck, the span is kind of long - 20' post to post. loading is 265 plf. at first i had spec'd lvl but do not want use that on an exterior application exposed to rain / moist. if i spec a built up beam w/ 1/2" x 11.25" A36 plate and (2) treated 2x12 SPF #2, does anyone have suggestions or details for thru bolt size / spacing? the plate would be primed and painted. thanks.

 

[COEngineeer]

You can use LVL if its not a drip trough deck(gypcrete top). You can also use Glue Lam or dropped steel beam. I am not sure what you are trying to do with the the plate. Composite section? Or you can use 14-16" deep timber so it is dropped a little.

 

[dik]

It's taking about 6' of tributary load and you might find 2x12's a little bouncy on 20'... You might consider glulam which can be obtained for damp environments. Alternatively you might be able to get a salvaged steel beam (W10x22) or possibly a W8x18 (I haven't checked the latter and I know the first works). These are common sections and may be available as salvage.

Dik

 

[IceNine]

TrusJoist makes a treated Parallam PSL that can be used in exterior applications.

http://www.ilevel.com/exterior/e_ParallamPSL_treated.aspx

 

[rnorth]

thanks ice9, i will check my options with treated parallam

 

[ctcray]

I'd check around with building supply companies and see what they can get. Here in Maryland I can get treated Glulams (24f-1.8E) easier than treated Paralams. I'd only use steel as last resort.

 

[SteveGregory]

If you use a steel beam, you will need it galvanized for contact with pressure-treated lumber or use a barrier to prevent corrosion.

 

[HouseBoy]

As others have indicated, if you use a flitch plate beam make sure you provide hot dip galvanized and/or proper corrosion pprotection from the CCA treated lumber for your plate and bolts.
Regarding bolting details, I would check for transfer of shear from the steel to the wood (for bearing) such that you might have 1/2" diam. at 16 inch oc staggered over the length of the beam and probably 2 columns of 2 bolts (1/2", 5/8" or 3/4") near each end. (meaning a total of 4 bolts at each end in 2 columns. I've not run any numbers but that seems likely to be what you would find from analysis. (Civil Engineering mag from September 1989 had a nice artical about flitch plate beams. I'm guessing you could google and find more recent articles. Probably fine homebuilding or Journal of light Construction would have something technical too.)

On the subject of treated PSL beams, I have seen problems with availability or lead time and/or shipping cost issues. I think the product is not commonly stocked and so, one piece might be harder to get (either more time to wait or high shipping cost for one piece.

 

[FSS]

There are now treated glulams available. Check

http://www.aitc-glulam.org

I don't like the treated parallams because they are expensive, hard to get, and have reduced capcities.

 

[rjgladish]

On 9 Nov 06 12:57, dik wrote

Alternatively you might be able to get a salvaged steel beam (W10x22) or possibly a W8x18 (I haven't checked the latter and I know the first works).

Where would you recommend locating salvaged beams?

Thanks,

rjgladish

 

[dik]

Call a local contractor and ask about salvage sources; he may have a beam... you may have to call a couple of them.

Dik