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Malamute
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# Posted: 27 Jul 2011 12:29 - Edited by: Malamute
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I've been looking for an applicable span rating chart that deals with 4x10's as floor joists. All I can find is related to using that size lumber as deck beams, which have different load characteristics. I'm wanting to use Lodgepole Pine rough cut 4x10's as floor joists, with a span of 17'4" max, 24" centers for an interior floor in an existing house. It will have 2x6 T&G subfloor (and as exposed ceiling in the lower room) with hickory for the finished floor above that.
I'd be cutting pockets in the existing logs for joist bearing points.
Thanks for any info.
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PlicketyCat
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# Posted: 28 Jul 2011 16:51
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You can try the AWC Calculator for joists and rafters, but all calcs and tables for joists and rafters are geared toward 2x dimensional lumber. Lodgepole Pine falls into the "Spruce - Pine - Fir" category.
They also have span tables for joists and rafters and structural design date for beams and timber available for PDF download (I think you only have to pay if you get a hardcopy).
You can also download their Post Frame Building guide.
If you know the total load calculations, you can also find beam calculators on the Forestry Forum. Joists, rafters and studs get some funky load offsets since they're repetitive members, but that's always in your favor if you did the load calcs based on single beam ratings.
In any case, we used #2 rough 2x12 Spruce, 16" oc on a 15' span with 60# LL (wood stove & water tank) and 10# DL and we passed structural checks with L/360 deflection (minimal bounce).
According to the calculators, you should be able to make 17'3" with #2 SPF 2x10, 12" oc... but wood is normally stronger by increasing depth rather than width, so I'm not sure if making that a 4x10 will get you double the spacing. But it would take you the same amount of wood to use 2x10 @ 12 as 4x10 @ 24 if you those 4x10's were ripped in half.
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PlicketyCat
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# Posted: 28 Jul 2011 19:14
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Alrighty - did some engineering math for you using the custom beam calculator, your spacing & spans, and adjusting for repetitive members
Design values for #2 SPF:
Fb= 575, I adjusted this by 1.15 for repetitive members to 661 (fiber stress in bending -- sagging)
E= 1.0 (modulus of Elasticity -- bounciness)
Fv, shear=125 (breaking failure)
Load formula is span x spacing x (live load + dead load)
Load for 17'4" @ 24" oc and average design values for stick framed living spaces
area = 208"x 24"= 4992 sq in / 144 = 34.6 sq ft
load = 40 psf + 10 psf = 50 psf (normal design average for living spaces and building materials)
Total Load = 34.6 * 50 = 1730 lbs
Plugged in to the calculator, 4x10 rough @ 24" oc fails bending and deflection -- it will sag and bounce over 17'4" (208") span.
However, a 4x12 rough @ 24" passes all metrics... so, if your subfloor and decking adds up to 2 or more inches in depth, you should be able to make the span without sagging or bounce. But you might be pushing it, especially if you have more live load or any heavy point loads.
So let's try with 4x10 @ 16" oc.
area = 208"x 16"= 3328 sq in / 144 = 23.1 sq ft
load = 40 psf + 10 psf = 50 psf (normal design average for living spaces and building materials)
Total Load = 23.1 * 50 = 1155 lbs
Plugged in to the calculator, 4x10 rough @ 16" oc passes all metrics. Subfloor and decking would just provide additional strength and rigidity.
Hope this helps :)
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Malamute
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# Posted: 29 Jul 2011 02:52
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It does help, thanks for the input. The owner wanted to keep it open feeling, hence the 24" spacing. Using 2x6 T&G for subfloor and hickory flooring, the total flooring thickness will be more than 2". Both should add some rigidity.
I don't know if I can get 4x12's cut or not.
I had the calculators you mentioned, but like you said, they are geared towards planed 2x material.
The center of the room has a fireplace/chimney that is about 3' thick and about 6' wide. The floor will surround that, the max span goes to the rear edge of the chimney, the actual span will be less at that point, so that will help some in the overall picture.
I don't think there will be any exceptional live load. He mentioned putting his Christmas tree there, but otherwise pretty standard living space.
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PlicketyCat
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# Posted: 29 Jul 2011 05:14
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So are these exposed upstairs floor/ceiling joists? I'm a bit confused about wanting an "open feeling" if these are under the main floor... unless he hangs out in his crawlspace a lot ;)
Anyway, if these are the upstairs floor/ceiling joists exposed to the main floor and that story is only bedrooms/storage etc, you can knock the live weight down to 30 psf unless they have massive furniture like waterbeds and pool tables up there. If that's the case, then the load is down to 1384, and a 4x10 will totally handle the 17'4" span 24" oc.
But in any case, twiddling the numbers, the total joist depth to get it to pass with 40 psf was only 10.25", so any type of solid flooring would make it. The 2" minimum with T&G sub and hickory finish should keep the floor from sagging and bouncing.
I'm assuming that there will be some sort of vertical support for the joists surrounding that fireplace chimney and taking all that load down to the ground. Which way is the FP running? Perpendicular to or parallel with the ridge/joists? Just trying to figure out how many joists are going to be split and in possible need of sistering and bridging to transfer the load if the FP knockout framing isn't supported by verticals. Better you than me, heavy/big fireplaces are nightmares to size framing under if they aren't actually sitting on solid ground.
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Malamute
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# Posted: 29 Jul 2011 11:15 - Edited by: Malamute
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The fireplace is perpendicular to the joist/ridge direction. I was going to tie into the face of it fo some support, it's rock faced with concrete block under the facing. I'm starting layout centered on the room/fireplace, as the opposing wall is pointed in the center. I was going to bridge to the next full length joists on both sides of the fireplace as well.
The current room is about 25 or so feet high, with a balcony/walkway between the stairs and the upstairs rooms. The owner doesnt like the huge open effect, but liked the idea of the beams being open underneath, instead of a closed/finished looking ceiling. it's a largish log home.
The proposed new room will be sort of a living room/den sort of room. They have a main living room on the current ground floor, but wanted to bring the ceiling down some, and have a sitting room/den sort of thing in the upper level. All of the common exterior wall of the current/proposed room has windows with a spectacular view of the mountains. He keeps talking about how nice it will be to sit and drink coffee in the new lower ceilinged room (he really doesn't like the extra high ceiling), and have spare room above for a TV room, and as extra living space for company, since the upstairs has only two bedrooms and "all that wasted space".
Was looking for pics, I don't have any of the room.
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