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Old 05-21-2008, 10:40 PM   #1
buddy6752
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Default 20 foot clearspan beam size

I just built my 30x60x14 shop. It basically has 3 20 foot bays between the large I-Beam steel structural supports. At on end, I want to build a second floor storage area. 19 feet in length (between the steel supports) and 8 feet deep ( one sheet of plywood). What size wood beam is needed to span the 19 feet? I would prefer a clearspan, but I can add a support midway if it would be easier. Can I glue and screw some 2x4 or 2x6 into a laminate that would span 19 feet?

I was thinking that if I used a support midway, I could glue and screw two 2x10x12's staggering the joints and stand them on edge. I was going to use 2x8x8 floor joists and 1/2 inch plywood subfloor.

The corner posts are to be 8x8 or 8x10 pine. The guy I bought the property from left a stack. I was going to notch the posts for the beam.

Here are a couple pics showing the corner for the second floor. Under the Loft will be a office/restroom.
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Old 05-21-2008, 11:50 PM   #2
Will67
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Default Re: 20 foot clearspan beam size

Homemade glulam beam

I would advise against that.

I would suggest looking for a structural engineer with a PE stamp.
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Old 05-22-2008, 08:02 AM   #3
buening
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Default Re: 20 foot clearspan beam size

This may sound kind of dumb, but what will you be storing up there? Will the storage be stacked to the ceiling? Anticipated loading can help us get a better idea.

The main issue will be the existing wall that the long beam will attach to. Is there a steel column that the beam can attach to?
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Old 05-22-2008, 09:18 AM   #4
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Default Re: 20 foot clearspan beam size

It will be for "stuff", i.e. fenders/seats/wheels/spare beer..ect. No engine blocks or bar steel.

It wont be stacked to the ceiling.

More like interior parts and front end sheetmetal when restoring rods to prevent dings from the parts laying around the shop.

I was thinking of a free standing loft, 8x10 pine post at all four corners and perhaps a 8x10 post midspan (to make the long span 9.5 feet between supports).
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Old 05-22-2008, 11:15 AM   #5
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Default Re: 20 foot clearspan beam size

Carpenters do this all the time. They are called “Fisk Plates” (often miss-pronounced as “fish plates.”)
You make a Fisk plate by sandwiching a piece of ½ inch steel between two 2x’s. A random pattern of ½ inch carriage bolts holds the sandwich together.
A good lumber yard will have the steel.
But do not get short 2x12’s get full length 20 footers.
With 2 foot spacing you will need 4 of them.
Your 8x’s as posts will be fine.
Use ¾ inch tongue and grove plywood for your floor.
Paint both sides white before you put it down.
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Old 05-22-2008, 11:59 AM   #6
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Default Re: 20 foot clearspan beam size

I used 2x10's for the ceiling joist's of my garage which is 20' wide, clearspan.
The 2x10's were the minimum i could go with when looking at the span tables for the 20' span. 2x12x20's would be a good suggestion, and 2x10's as a minimum; get the best species you can...and don't forget to check the crown when you put them in.
My attic floor is pretty solid, and the 2x10's do a good job; you'd have to have a lot of fender's up there to see any deflection.
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Old 05-22-2008, 12:30 PM   #7
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Default Re: 20 foot clearspan beam size

Flitch Plate

http://en.wikipedia.org/wiki/Flitch_beam
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Old 05-22-2008, 01:03 PM   #8
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Default Re: 20 foot clearspan beam size

Twenty foot is quite a span for wood in a storage application - especially considering that chances are good that you will end up putting more up there than you are initially planning on...

I'd look into the i-joists rather than dimensional lumber. You can start here: http://www.i-joist.org/home.asp

Here is the design guidelines: http://www.i-joist.org/pdf/Asd_ij.pdf

And here is Trus-Joist's information - span charts are on page five: http://www.ilevel.com/literature/TJ-4000.pdf

My second floor woodshop is designed for 100psf for reference.
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Old 05-22-2008, 06:02 PM   #9
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Default Re: 20 foot clearspan beam size

So, it would appear that a 20 foot clearspan is out. If I put a 8x10 post half way on the long span, making two 9.5 foot spans, can I double up a pair of 2x10 or 2x12 for the "girder" and set the 2x8x8foot floor joists on top?
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Old 05-22-2008, 06:47 PM   #10
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Default Re: 20 foot clearspan beam size

Chart on page five shows a 14" or 16" TJI560 would work for a 20' span.
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Old 05-22-2008, 09:08 PM   #11
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Default Re: 20 foot clearspan beam size

Ummm... If I understand the problem, you only need to span 20' ONCE (or at most twice) to form the "beams". Then your floor joists only need to span 8' between the wall and the "beam" (or between the beams).

In that case, you need something like a 12-16" GLULAM or LVL to span the 20' and can use simple 2x8-10 dimensional lumber 16"OC as floor joists.

FWIW the lumber that forms the beams in the "pier and bean foundation" for our cabin are 36 ft long glued and screwed overlapped 2x12s. BUT they only span a max of 12' between piers. The floor joists between them are 2x10s 16" OC where they span 16'.

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Old 05-23-2008, 10:06 AM   #12
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Default Re: 20 foot clearspan beam size

Running some quick numbers and only checking bending:

For the 19' span using 2x12s bolted together (neglecting the steel plate, don't have time to do a transformed section calc for the steel plate) and using 100psf loading, you get a bending stress of 3400psi and a typical allowable bending stress is 750psi depending on the wood type. Shear in the beam is 169psi and allowable is 70psi

For the 9.5' span using same loading and beam size, the bending stress is down to 860 psi. This is still higher than the allowable but is assuming 100psf. This would be on the high side if you plan on loading it pretty light, but remember that 100psf includes the weight of the platform. Shear in the beam is 84psi and allowable is 70psi

Both situations assume that the platform is separate from the building frame structure and you have a beam on each side of the long sides, so there is only a 4' wide load tributary area on each beam. You would have to run a cost comparison on using these beams compared to glulams, but another option would to have a beam in the center of the platform. You would now have three beams, which would reduce the load tributary area. You would have to beef up the end joists, as the center beam would be connecting to this. No calcs have been done for that option.

I did not look into glulams, as others have that pretty much covered and there are charts all over the place. Whatever you do, pay special attention to the connections of the joists to the beams, beams to the columns, and the columns to the concrete. The details is where people run into trouble, i.e. toenailing or using wrong screw type. I would suggest using Simpson-type joist/column brackets throughout.
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Old 05-23-2008, 10:57 AM   #13
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Default Re: 20 foot clearspan beam size

Thanks for the spelling lesson ab.
I just knew for sure it wasn't "fish".
I wince every time I hear it on a job site.
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Old 02-03-2010, 02:43 PM   #14
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Default Re: 20 foot clearspan beam size

Hi I am not sure whether to start a new discussion or just post here so forgive me if I'm doing it wrong. I found this forum because of the discussion of a 20 foot beam. We have a 16 foot patio door that was installed this summer with a made on site beam with 2X12's. It is sagging and the slider will not open. The installer is being fine about replacing with whatever we want a laminated premade beam or "LDL" beam. Not sure which would be strongest. The roof (raised heel truss) slopes to the wall with the slider. Slider is on the upper floor and we haev 2X6 exterior walls. Any advice would be appreciated. Thank you!
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