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Author Topic: could you use a 4''x6'' in place of a 2''x12''  (Read 2596 times)

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Offline Rod

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could you use a 4''x6'' in place of a 2''x12''
« on: September 10, 2004, 06:40:11 PM »
for floor joist.The reason is, I can find more 4''x6'',or 6''x6'' ,then 2''x12''... ;D :) :o

Offline raycon

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Re: could you use a 4''x6'' in place of a 2''x12''
« Reply #1 on: September 10, 2004, 06:54:28 PM »
 You'd need a 16" wide  beam to get the same stiffness.

You can figure it out by calculating the first moment of inertia.  
= (1/2)*base*height^3

the 2x12 = 288 in^4
to find the equivalent for a 6in tall member = 288/((1/12)*6^3)
which is think is 16" or so. You'd have to redo your floor loads since they probably sag from the joist weight. I could be off since I'm sitting here having a few cold ones but thats the idea.
You could do a couple of things similar to making your own trusses but I can' t type that could draw it and show you where the stresses need to be watched.
Lot of stuff..

Offline beenthere

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Re: could you use a 4''x6'' in place of a 2''x12''
« Reply #2 on: September 10, 2004, 06:55:27 PM »
The are not comparable (even assumming both are clear wood with no knots or grain deviations - as that's another story).

Best way to explain is, although it may seem like the same 'area' of wood in cross section, you wouldn't expect the same strength and stiffness from the 2x12 laid flat as you would the 2x12 on edge.

The depth of the joist is important in the load it will carry and the stiffness it will provide.

(and what Ray said just before me  :D  )
south central Wisconsin
 It may be that my sole purpose in life is simply to serve as a warning to others

Offline Furby

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Re: could you use a 4''x6'' in place of a 2''x12''
« Reply #3 on: September 10, 2004, 07:16:23 PM »
While you are both right, it also depends on span and spacing.

Offline Tom

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Re: could you use a 4''x6'' in place of a 2''x12''
« Reply #4 on: September 10, 2004, 07:26:21 PM »
Years ago, I was told that a good rule of thumb was that "an inch in depth is worth almost 3 inches in width. :)
extinct

Offline EZ

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Re: could you use a 4''x6'' in place of a 2''x12''
« Reply #5 on: September 11, 2004, 06:04:57 AM »
You would be better off to use 2x8's than 4x6 or 6x6. But, Iwould go with 2x10 or 2x12.
EZ

Offline sigidi

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Re: could you use a 4''x6'' in place of a 2''x12''
« Reply #6 on: September 11, 2004, 07:15:18 AM »
Hey Rod,

I guess you'll be tired of hearing it but... strength in timber lies in its depth. obviously acepting everything else is the same.

On the flip side I have a handy program which calculates beam sizes - it may be a bit different as it conforms to Australian Standards, but given floor type, building levels, continuous/single span, span spacing and material type to use for the specific floor framing member it will calculate possible options. Also taken into consideration is wind category for the building, are you building in cyclonic or non-cyclonic area, what about wind speeds high, med or low?

If you wanted a quick idea let me know the details and I can give you some options using different materials.

FYI - I'm studying here in Oz to be a Civil Drafter.
Always willing to help - Allan

Offline Rod

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Re: could you use a 4''x6'' in place of a 2''x12''
« Reply #7 on: September 11, 2004, 09:31:54 AM »
sigidi,what about a 6''x6'' hemlock beam 12 long spacded every 2 foot On Center with 1 1/2'' x 6'' hemlock flooring. :o

can you figure that out with your program? :) ???


I live in West Viginia and we don't get much wind in these pasts. ;D

Offline Rod

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Re: could you use a 4''x6'' in place of a 2''x12''
« Reply #8 on: September 11, 2004, 09:44:39 AM »
I knew that the strength in timber lies in its depth.

I've seen those i joist made with 1/2 OSB that can clear some really long spans. 8)

If I had a chipper to chip the logs and the equipment to glue the chips back together I might save a few board feet. :D



Offline D._Frederick

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Re: could you use a 4''x6'' in place of a 2''x12''
« Reply #9 on: September 11, 2004, 10:05:04 AM »
Rod,

Glue your  4 x 6  together to give you the 12 inches, should give you the strength.

Offline sigidi

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Re: could you use a 4''x6'' in place of a 2''x12''
« Reply #10 on: September 12, 2004, 05:29:33 AM »
Quote
sigidi,what about a 6''x6'' hemlock beam 12 long spacded every 2 foot On Center with 1 1/2'' x 6'' hemlock flooring. :o

can you figure that out with your program? :) ???


I live in West Viginia and we don't get much wind in these pasts. ;D



Rod Sorry to be a stick in the mud but we don't have any o that hemlock stuff down this end o the world, what about a good ol bit of seasoned pine :)

Seriously the program only gives options in different grades of seasoned/unseasoned pine, hardwood and manufatured beams like 'I' beams sorry if I threw you a curve
Always willing to help - Allan

Offline karl

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Re: could you use a 4''x6'' in place of a 2''x12''
« Reply #11 on: September 12, 2004, 07:08:20 AM »
Again- depth is key.
What are your spans? How about loading - both dead and live? .If you can reduce span with beams/partitions, maybe you can safely use smaller dimension.
Eastern Hemlock/Tamarack- 40# sq ' live load -2x8 ,16" oc #2 stock span=11'4", 12' for #1 and select. Same materials 24 oc=10 and 10'6".
2x10- 16" oc -14' 6" and 15' 3"
        24 0c- 12' 8" and 13' 4"
Be aware these are for material w/ moisture at 15%- green lumber has less strenght and may sag before drying
Green = 5/8 the strength of dry +/-
"I ask for wisdom and strength, Not to be superior to my brothers, but to be able to fight my greatest enemy, myself"  - from Ojibwa Prayer.

Offline MrMoo

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Re: could you use a 4''x6'' in place of a 2''x12''
« Reply #12 on: September 13, 2004, 08:18:10 AM »
Karl,
Did you look that information up in a book? I have been looking for a book that would list spanning strengths for different types of wood. Or at least give a formula that you could figure it from,
Mike

Offline Bruce_A

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Re: could you use a 4''x6'' in place of a 2''x12''
« Reply #13 on: September 13, 2004, 08:39:08 AM »
You need to get the lastest version of the national "Uniform building codes" book.

Offline Jim_Rogers

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Re: could you use a 4''x6'' in place of a 2''x12''
« Reply #14 on: September 13, 2004, 04:34:13 PM »
You can go to a site and download a free version of a beam calculator.
You can also download a manual that teaches you how to figure your loads and areas so you can input the right numbers into the program.
The limits on this program are that you can't input full dimension lumber. If you input a 2x12 they will reduce it to a 1.5 x 11.25 and this doesn't work for us that build with full dimension lumber.
Any way the site is http://www.beamchek.com
There are some limits to what the free version will do.
If you need to figure a beam that is longer than the free version will do, drop me a private email with all the inputs and I'll run it threw my version that I bought.
Jim Rogers
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

Offline karl

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Re: could you use a 4''x6'' in place of a 2''x12''
« Reply #15 on: September 13, 2004, 05:30:03 PM »
Ya caught me ;) Hope nobody thought I pulled those spans off the top of my head-
Got the info from "the PocketSize Carpenters Helper"- don't know if it is still in print, got mine years ago from RS Wood and Co. Box 430 Liberty, Me. 04949

Sounds like that there Beamchek site should be the cheap answer.
"I ask for wisdom and strength, Not to be superior to my brothers, but to be able to fight my greatest enemy, myself"  - from Ojibwa Prayer.


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