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Old 07-15-2013, 11:51 AM   #1
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How do I construct a flitched beam?


Hi all,
I have found out it is possible to span 20' for my trusses that I have on the roof of my deck. Nice people on this forum said that it was possible to do it with a couple of 2x8's along with a 1/4" piece of steel sandwiched in between them.

The questions that I is how do I construct it to get the most strength out of it. 90% of the load on the beam will be dead load with maybe 10% or so being live load (putting a swing or 2 under the roof)

Do I get a couple of 12' and 8' and then stagger them?

Any thoughts??? Thanks in advance.

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Old 07-15-2013, 03:30 PM   #2
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How do I construct a flitched beam?


Assuming you can't get 20 ft lengths, it would be more structurally efficient to centre the 12 fts on the centre of the beam, and use a 4 ft each end.

However, that might be the least of the problems. Depending on the actual load you are carrying, I suspect with an 8" deep beam spanning 20 ft, that you might have excessive deflection.

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Old 07-15-2013, 03:42 PM   #3
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How do I construct a flitched beam?


Might be better to use LVL as opposed to a flitch beam,lighter and maybe cheaper to construct,Daniel Holzman on this forum may be along,and he could tell you i'm sure as he's a civil engineer.
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Old 07-15-2013, 03:57 PM   #4
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How do I construct a flitched beam?


Is it possible to get an LVL that is rated for the elements? I know that I could easily get some 2x8's that are pressure treated and that would do the job.

As for the excessive deflection there isn't going to be anything on the roof, just thin metal. And I will be placing the swings close to where the trusses tie into my cabin. The deck will just have an open front, however if you think that it will have that much deflection to raise concern I may have to figure something else out.

Thanks once again.
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Old 07-15-2013, 04:25 PM   #5
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How do I construct a flitched beam?


what building code does your area use? most building codes require a minimum deflection even on roof assemblies.
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Old 07-15-2013, 05:04 PM   #6
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How do I construct a flitched beam?


GBrackins, I really dont know, to be honest this is just something that is going out in the middle of no where, where the biggest problem I might have with it is a raccoon taking a nap on it.

Just need something that will hold the weight of the roof plus a swing or 2. We don't get much snow here so that isn't really an issue.
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Old 07-15-2013, 05:53 PM   #7
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How do I construct a flitched beam?


You should be able to find 20 foot lengths of 2x8--or 2x10 without much trouble.

Such a thin beam will tend to roll over under load---tong.g is an engineer also,if my memory is correct---
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Old 07-15-2013, 05:56 PM   #8
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How do I construct a flitched beam?


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Old 07-15-2013, 06:15 PM   #9
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How do I construct a flitched beam?


A flitch beam is a sandwich of steel plate and typically sawn wood, so a metal plate sandwiched between a pair of 2x8's would be a flitch beam. Flitch beams are commonly used to strengthen an existing beam where it is difficult to remove the existing beam and replace with a stronger beam. Flitch beams are rarely used in new construction (at least I have never seen one used in new construction) because it is almost always less expensive and easier to use an LVL or a Glulam, and if they aren't strong enough, use a steel I beam.

I am not in the business of designing structures over the internet, but I suggest you visit a local lumberyard (NOT a big box store) and ask them to size and furnish an appropriate LVL or similar beam for you. A real lumberyard may well have an engineer on call who can size the beam for you, of course the cost of sizing the beam will be included in the price of the beam, but it will be much less expensive than hiring your own structural engineer for what sounds like a pretty simple project.

As for outdoor use, you say you are going to have a roof, so I don't understand the problem, the beam should be under the roof, hence it would be no different than any other beam in your house, and there should be no need for PT lumber. If part of the beam is going to extend beyond the roof for some aesthetic reason, ask the lumberyard what type of treatment is required, a real lumberyard should be happy to discuss paint, stain, varnish, or epoxy coatings that will function effectively in your environment.
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Old 07-18-2013, 07:02 PM   #10
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How do I construct a flitched beam?


Daniel,
Thanks for the reply, sounds to me like an lvl beam is the way to go with it, just one question though. Is there an lvl beam that could be used outside, it will not be exposed to direct rain/sun etc. Just the humidity in the air/temp and so forth.


Thanks once again everyone for the input.
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Old 07-18-2013, 08:45 PM   #11
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How do I construct a flitched beam?


I've built many a flitch beam. All of them were designed by an engineer. Otherwise you're just guessing, and guessing at structural framing is asking for trouble.

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