In the july 2001 FHB there is a house built by Glen Irani… where he uses 3 1/8 glue lams laid flat supported on steel i-beams for a loft/second floor area… I’m doing a project where we need to build a loft area and keep as much headroom up & down as we can and still split a floor… what i need to know is…
what kind of span and loads can i get out of a laid flat 12” wide glue-lam?…
each loft will be aprox 16′ wide and 20′ deep… i have a brick wall at one 16′ end and a cross beam at 15’… would these span 5′ … 7.5′ ? anyone have a clue on where i could find out
thanks in advance
Craig [email protected]
Replies
I'm not real clear with how you've described your spans. If you're spans are only "5'...7.5,'" my gut tells me you're probably OK, but bear in mind that a glue lam is designed to function in vertical cross section. If your span is getting out there in the 12' + area. you'd be advised to get the blessing of a PE (professional engineer).
There was a thread sometime back, early last summer maybe, about someone who, like you, was trying to maximize headroom and there was a discussion about a diaphram-type construction, kind of on the boxbeam concept, using plywood surfaces glued and screwed to a wood structural web. As I recall, there was some positive feedback on it.
Maybe somebody with a better memory than me will jump in here and point you in that direction.
Jules Quaver for President 2004
basicly it's a 15' x 20' loft area (9 of em) i have a brick wall at the back for a ledger... then i have 8x8 posts going to the roof 15' out from the wall... i can put a load bearing beam across the posts for one support... (i hope a 8" I-beam) but between the back wall and the post... try'n to find out do i need one more I-beam (7.5ft span or 2 for a 5' span... then catilever the forward most 5' past the beam attached to the 8x8 posts... cost wise since i end up with a floor & ceiling basicly ready for finish it works out pretty well... (about $1350.00 per loft for glue-lams)... thanks for your input...
oh yeah... thought i'd put a 1/4" edge grove in em and spline em.. predrill the i'beam and mechanical fasten em from the bottom... leave em off the side walls with a 3/8" foam gasket and run my trim top & bottom....
Edited 1/18/2003 3:39:03 PM ET by ponytl
If the glulam is laid flat, it doesn't really have any more strength than a few 2X4s laid next to each other.
There are some SYP span charts here:
http://www.southernpine.com/tables/2.htm
Unfortunately they don't cover 2X4. You might look at getting some high grade 2X4 from a truss plant, and using them as conventional floor joists. It would sure be cheaper that using glulams.
Snowmobiles: Natural selection at its finest.
>> If the glulam is laid flat, it doesn't really have any more strength than
>> a few 2X4s laid next to each other.
Slightly less, actually, because it's not even as thick as a 2x4 is wide. A board 1-1/2" x 3-1/8" with the 3-1/8" dimension vertical will have 42% of the strength of a 2x8, and 7% of the stiffness, all else being equal. 10.7 of them glued together for a width of 16" will have 444% of the strength and 78% of the stiffness of a 2x8.
As Boss has pointed out before, even if 78% of the stiffness of a 2x8 is enough to meet the deflection limits of your situation, the floor may still feel bouncy if the resonant frequency of the whole floor assembly is too low. Your span may be short enough that that won't be a problem.
I sure hope some engineer chimes in here, but I think there is great strength in a glulam layed over on it's side - way more than the same number of 2x4's nailed together would have, and WAY more than simply multiplying the individual span strength times the number of boards.
As I understand it, horizontal structural member most often fail when the center rolls over towards horizontal, even if the two ends are secured upright. You've probably seen this many times, where the middle section of an overloaded ceiling joist starts to lean, or twist. (came back to say that that's why midspan blocking and cross bridging strengthen a span, because they keep the middle of those framing members from rolling under load)
So my thinking would be, that the glulam is alot stronger because there no way for those individual 2xs to roll, and I am having a real tough time imagining the entire beam rolling into what would be vertical.
In fact, I think I remember a friend telling me he was renovating some turn of the century flat roofed commercial buildings in Tacoma, and that's exactly how the roofs were were framed, 2x4s on edge, nailed together across the entire width of the building.
Now as for that ledger on a brick wall, I think you might have some problems there. At least if you are working in any type of siesmic sensitive area. I'd be interested to hear how you intend to do that.
Edited 1/18/2003 7:39:33 PM ET by jim blodgett
>> ... and WAY more than simply multiplying the individual span strength
>> times the number of boards.
Why do you believe that? If you double the width of a beam, you double the strength and stiffness. If you make a 3-1/2" x 15" glulam by gluing 10 2x4's together and then lay it on its side, it is exactly 10 times as strong and 10 times as stiff as one 2x4 in the same orientation.
I have to side with Jimbo on this one . A 2x4 sistered will be stronger , but if you use some good glue and then glue 10 together the srength will be greater then 10 sitting against one another. now If I read his post he wants to fill his whole opening with g,lam one abutting the other and glued together should make for a very stought floor . If that is not srong enough try the 2x6 g,lam
Uncle Dunc - you said, ">> ... and WAY more than simply multiplying the individual span strength >> times the number of boards.
Why do you believe that?"
Let's see if I can say this...first off, the thing I said earlier about the way a horizontal framing member fails, by rolling.
But there's more. And I can't cite any engineering background or facts here, Dunc, but I'll try my best to explain my thinking.
Let's say a 2x4 spanning 8 feet is rated to carry x number of psf. Okay, tests have been performed under controlled conditions and the data studied by qualified people to get that rating, right?
So we all know that there will be parts of that 2x4 that are weak points, like at a dead knot, or where the grain runs off the edge of the board, right? But all that gets factored in and an average is calculated of many tests to come up with the expected strength of the average 2x4 of any given grade.
If you sister two 2x4's together, the weak points in one stick are unlikely to be aligned with the weak points in the other - so two would carry more than twice the amount of one, three more than three times and so on.
I don't know, it just seems right. Do you think I'm basing this on a faulty premise?
Edited 1/19/2003 1:45:17 AM ET by jim blodgett
I can see the sense of that. My calculations were based on the theoretical behavior of beams, assuming that wood is perfectly uniform, like steel. Which it's not.
However, I don't think it would be a good idea to _depend_ on getting a more than linear increase in strength or stiffness as a basis for design decisions. If your design depends on getting 210% of the stiffness a single joist by gluing two of them together, what happens if you get two that do have their weak spot in the same place?
"If you sister two 2x4's together, the weak points in one stick are unlikely to be aligned with the weak points in the other - so two would carry more than twice the amount of one, three more than three times and so on."
That's basically true. The NDS allows you to take a 15% increase in the bending value for lumber that's sheated with plywood, if there are 3 or more in a row and less than 24" O.C. This applies to most residential framing.Prevent death on the road. Drive on the sidewalk
Remember you are talking 2xs with a space between them and sheeted with ply they still have room to roll. Now if they are glued to each other ,effectivly making them wider than tall they'll tend not to roll.
I would feel safer on a gluelam of 2x3s 10"laid flat than on a 3x10 laid flat spanning that space. I t would be like the scafold planks that Jim made up out of 2x and ply . Stout enough for aunt Tilly and her keg of beer.
By the way Jim I made up acouple of those planks .Work great !
You're partly right, I think.
Using a Glulam would keep them from rolling if they were maxed out. But so would plywood glued and nailed on top of conventional floor joists.Diagonally parked in a parallel universe.
The companies that make gluelam beams will make you a beam any width and height you want. They will also size them for you, so don't settle on the product that is available at your local lumber yard when you can special order the beam you need.
Parallam beams can also be special ordered in any size.
I can't give you engineering, but I saw a TOH episode on a scandinavian townhome development where they did this on all the floors. I think the max span was 12'.
I would have absolutely no concern about failure - you could park a car on it - but I would wonder about shrinkage and expantion from season to season. Seems to me a 15' wide sheet of pine could easily move 2'' or more back & forth.
This is an old produce warehouse in memphis on the mississippi river I have enough ceiling height to split the floors (just under 17') as long as i keep the floor as slim as i can... and can you guys say "cheap" it's not that I am... it's what i have to be... it's a warehouse... and i can use cheap materials... polished/cut concrete floors, no 2 units have to be the same (20 of em) so I scrounge materials... buy overruns overstocks... ect...
I'm not sure on the movement of 15 3 1/8 x 12x 20' glue-lams laid side x side and i'm in the hope that i can get a 90" span out of them...( if i have to go to 60" i can, it just adds to my already strapped budget) it's a sleeping loft with a bathroom (shower no tub) so it won't be high loads (no waterbeds i hope)...
what do you guys thing about spline'n em maybe 1/2' deep x 1/4 cut on each butting side with 7/8 x 1/4 spline.... that'd be 3000 or so ft of routing... so would it be worth it?
90" span? I wouldn't bother with a spline. After all the input here, it seems you're going to have a pretty firm floor. To join the beams you could dowel them if you care to on about 2' centers...table leaf effect. No science here, just a thought. But if they're firmly attached to bearing surfaces below, they're probably not going anywhere. Lams are made of kiln-dried wood after all.Jules Quaver for President 2004