Built up beam question

[JeffC]

I'm finally starting on my project (16'x22') cottage/cabin.  I will be using a post and pier foundation, and built-up beams made from three pressure treated #1yellow pine 2x12s, attached with Simpson ABU66Z brackets.  Since the brackets are 51/2" wide, one way to make up the difference is to rip 1/2" PT plywood and laminate as per John's tutorial.  Since the plywood doesn't add much strength, I have also thought about using four (4) 2x12s (which would be 6" wide) and then just using a router to mortise the inside 2x12 and allow the braket to fit.  Are there any disdavantage to going with this approach?  It seems like it would not be any more work (than ripping the plywood), add more strength (the inside 2x12 would only be mortised about 1/2"), and wouldn't cost any more (at least with my local lumber prices).  Any thoughts?

Thanks.  

[youngins]

Just as an FYI - I did a double built up beam with 2 1/4" pieces of plywood and it came out a little wider than I expected and almost did not make it into my PB44Z's. .  I believe it is because the PT 2x6's were a little wider than anticipated.  Next time I run into this, I might just use 1 1/4" spacer instead.

[John Raabe]

Using a router to cut down the beam to fit the seat is not a bad idea. The bearing area of the beam will still have plenty of square inches.  8-)

Remember to glue up the composite beam and keep the nails out of the bearing points until after you have the thing ground down to fit the supports. Nails can slow down a router quite a bit.

[Kodakjello]

I'm doing the same thing with my beams but I thought the plywood laminated in between the 2x12s would add quite a bit of strength. I have yet to test this but an article on Backwoods Home Magazine got me thinking years ago....http://www.backwoodshome.com/articles/fallick49.html. It suggests that as long as the plywood remains upright, it adds quite a bit of strength. Even better is a thin steel plate.

[JeffC]

Thanks for the thoughts.  The plywood approach looks like it might be just as good, so the decision now looks like I'll go with whatever is easier.   With #1 yellow pine, the beam is more than stiff enough with either approach (three #1 2x12s provides an L360 total load of 2310# plf with 6' spacing).  Plywood or a fourth 2x12 should bring it up close to 2750# per linear foot!