Laminated Timber Beams

[Everynameistaken]

Hi All,

I have a question regarding building a built-up timber beam out of 2x12

We have spec'd solid sam members and they cannot get them in time.

The code has tables for 5-ply built-up sections but does anyone see any reason why a 6-ply would be a problem? Need it for capacity.

As an alternate I could try 2 4-ply built-up beams. Make the 4-ply beams with nails per the code, them thru bolt the two built-up beams together to get a new huge beam??

Thoughts?

 

[Shotzie]

Could you not go with a structural composite lumber beam instead? I don't know if you'd get the composite action you're after if you use a 4 ply nailed beam with 2 plies bolted on.

 

[jayrod12]

You'd need to look at how the beam was loaded and what the fasteners would need to do to accommodate the load transfer between plies.

6 plys is not out of the question. But it does beg the question, why not engineered lumber like LSL or LVL. It would likely be much easier in the end.

 

[Everynameistaken]

Good questions!

The application is an exterior rehabilitation of an existing facility and not for a residential building. The existing structure is all old creosote treated large timber products. Not too sure I should be using LVL outside in the elements, but pressure treated DFL should be fine.

The member would be loaded onto by a nail laminated deck which would extend fully over the built-up beams so not asking the nails in the built-up to pull to all the ply's from a face mounted hanger.

 

[jayrod12]

Then I don't see a 6 ply being an issue, I'd just be overly conservative with the bolting specification.

Stainless steel or hot-dipped galvanized bolts (not sure if HDG bolts even exist).

LVL and LSL do not have approved exterior grades, but there is a Parallam Plus product that is approved for outdoor use.

 

[KootK]

Sounds workable with the top loading. I would also be worried about LVL outdoors. If needed, I believe that parallam can be made outdoor appropriate.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[dhengr]

Everynameistaken:
I should think that what you want to do with the 6-ply treated DFL would be o.k., since it is uniformly top loaded. But, a couple things you might consider: 1.) cover the top with a piece of rubberized peal-n-stick flashing material to keep any water out from btwn. the plys; 2.) maybe consider using some of the newer structural screws from both sides, of the proper length 8" +, otherwise you are going to have a pin cushion of a beam. The screws will likely pull the whole beam together better after some initial build-up nailing. Apply a few more screws out at each bearing end just to help tie thing together.; 3.) have someone clean up the bearing ends so you actually have more than 2-2x’s bearing.

 

[Everynameistaken]

Thanks guys,

All in line with what I was thinking. A few great ideas like the peel and stick!

Thanks

 

[mike20793]

For this application, I would try to use the Simpson engineered wood ply screws. They have handy load tables that makes it easy to select a pattern based on your loading. The PSL Plus are only readily available in the northwest US and in Canada, or so I've been told. When I need engineered lumber for an exterior application, I've been using Power Preserved Glulams. They work great and are actually pretty readily available and relatively inexpensive.