4x6 span tables?

Started by CjAl, April 16, 2013, 02:31:15 PM

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CjAl

I am having no luck finding  span table for 4x6 either dimensional or rough sawn. I want to us 4x for loft floor joists on 48'' centers and span 9' 4.5''. I will most likely have them miled actual size from souther yellow pine. Any point me to a table or tell menif i can do this with 4x6? Its a loft that will have my sons bedroom in it.


2x6 dimensional comes up at 9'4'' on 24'' centers

Squirl

I've seen don_p use that logic before.  4x6 48" O/C is the same amount of wood as 2x6 24" O/C


CjAl

Thats where my thinking was going. Its actually more wood if its actual size. I just cant find any tables for 4x except for major load bearing beams, headers or roof beams.

John Raabe

You are unlikely to find charts for that - especially for rough cut. I looked up in Charlie Wings' "From the Ground Up" and found a span chart for 37.5 psf load (sleeping room) and rough cut 4x6 @ 48" o/c. Doug Fir can span 10'- 10". You should be OK for just about any decent structural timbers. (Be advised that this chart is from 1976 so a quick calc from a real engineer could bring that up to date.)
None of us are as smart as all of us.

CjAl

Thanks for the info and the heads up.


MountainDon

And don't forget southern pine is being downrated as of June or July this year. Same wood as now, but officially it will no longer be as strong as past and most current information. None of the current tables I have compared differ from those in use a year ago, so I believe it is safe to assume most current tables reflect old/previous SP values.

Just because something has been done and has not failed, doesn't mean it is good design.

Don_P

There is a flaw in my logic of a 4x @48" center is equivalent to a 2x@24" ctrs. There is a 15% strength increase when members are spaced 24" or closer together that we can't take with widely spaced timbers.
Southern pine grading is... different. Right now 4x material is not derated.

One of my calcs for this type of problem is here (won't mean diddly to an inspector);
http://theownerbuiltcabin.com/calculators/TT/beamcalc.htm

I'll give you entries to start with
Load 1500 lbs
Span 112
width 3.5
depth5.5
These are for #2 syp 4x6
Fb 1250
E 1.6
Fv 175

you'll get a fail in deflection, one way is to bump the dimensions to rough sawn and it works. Use nicer, denser stock and the Fb and E numbers will go up a bit. However, the way deflection calcs are really done by engineers is to check deflection on the live load only not on the live + dead load. Use the dimensions 3.5 x 5.5 and enter 1120 for the load, click "show result" and deflection will pass.

You can run a check of that by opening the awc spancalc, run a scenario and then plug their design values into mine. a total load check will show mine conservative in deflection, you'll fail earlier on mine. A live load only check should come out mighty close on deflection, the controlling factor in this type of member.

comanche

Quote from: MountainDon on April 16, 2013, 06:10:12 PM
And don't forget southern pine is being downrated as of June or July this year. Same wood as now, but officially it will no longer be as strong as past and most current information. None of the current tables I have compared differ from those in use a year ago, so I believe it is safe to assume most current tables reflect old/previous SP values.

Do you know why it's being downrated? Just curious...
Homer, AK

MountainDon

The problems stem from new growth lumber. The timber is being grown so fast that the old published values are not being met. MSR lumber will not be affected by this change, only visually graded SP..

Info from the SPIB on the new values

...from the article...  The American Wood Council (AWC) will work with the International Code Council to incorporate the new design values into span tables in the 2015 International Building Code and 2015 International Residential Code.  So they are not exactly rushing this but it something to keep in mind.
Just because something has been done and has not failed, doesn't mean it is good design.


CjAl

 itbis looking likeni will just use 2x material on 24'' centers or 16'' centers for the sake of being available now. And ease of finish. The 4x on 48's requires 2x tongue Nd groove which would take me a while to come up with so i am making this sacrifice in the name of getting a roof up faster before i loose my subfloor.
I thoughtbi had a local sawmill guy who was going to cut me the lumber in tradE for trees off my other property but he has decided its too far to run his truck up there to get them to be worth his while.

Thanks for all the info though.

Don_P

Is it possible to get a portable mill in to make flooring, trim, porch posts, stair timbers....stuff further down the road in the build.
Often the school shops have open nights for the community where you can plane, tablesaw, etc, if you don't have those tools. Drying time is a problem. Just another option

CjAl

I have a local guybwith a mill i can get to cut stuff for me. He is a lot closer then this other guy but he already has more logs then room so he wasnt interested in a trade either. I start my new job wednesday so right now i have more to barter with then cash to buy. Selling a 357 magnum tomorrow and going to go get the lumber to get the loft floor joists in and some roofing to finish my wifes cat house. . . . No not that kind of cat house

UK4X4

4x6 fails on 48" spacing
4x6 passes on 32" spacing


4x8 passes on 48" spacing

Based on 9'5" span 12#dead and 30# live

according to Forte software

It looks real pretty when done !

SouthernTier

Quote from: Don_P on April 16, 2013, 10:57:21 PM
There is a flaw in my logic of a 4x @48" center is equivalent to a 2x@24" ctrs. There is a 15% strength increase when members are spaced 24" or closer together that we can't take with widely spaced timbers.

But not in 4X @24" center being equivalent to 2X @12" center?

As you may recall, I had to drop to 6" floor joists in order to meet the (somewhat arbitrary to me, but whatever) code requirement that 50% of my loft be greater than 7' in height.  You agreed that 2x6's @12" would meet code, but I would have to have my "eyes wide open" to the fact that it would be flexy.

Since I plan on T&G 2x6 flooring for the loft floor (exposed to below), I think things would look much nicer if I have 4x6's spaced @24" oc instead, possibly rough cut.  Do you think that would work?

Quote from: Don_P on April 16, 2013, 10:57:21 PM
One of my calcs for this type of problem is here (won't mean diddly to an inspector);
http://theownerbuiltcabin.com/calculators/TT/beamcalc.htm

I could run the calculator (and probably will when I get the chance), but as you say, won't mean diddly to the inspector.  I am trying to stick to code as much as I can so I don't need much PE review (right now, just for my ridge beam, I think).  Not sure if going with the 4x6's would work just sticking to code.  Also, if I get them local rough cut, I suppose the inspector could demand they be professionally graded.  I can get some good prices on local Amish-cut hemlock, but if I have to pay to get them graded, there goes my savings.


Don_P

QuoteQuote from: Don_P on April 16, 2013, 10:57:21 PM
There is a flaw in my logic of a 4x @48" center is equivalent to a 2x@24" ctrs. There is a 15% strength increase when members are spaced 24" or closer together that we can't take with widely spaced timbers.



But not in 4X @24" center being equivalent to 2X @12" center?


What we're talking about here is an adjustment factor, an increase in the bending strength of 15% that is allowed to be used if framing members are 24" or closer together (this applies to built up beams as well). So you can take the "repetitive member adjustment"

NY has a native lumber law, thank your local farmer and small sawyer, for residential it doesn't need a third party grading agency.

SouthernTier

Thanks Don.  I'd never get this cabin built without your help.

Of course it remains to be seen if it ever will get built, but if not it won't be for lack off trying  :)

Don_P

I hear you, I'm trying to get something built here and am swimming in the bycatch. Todays logging was kind of neat, I got the butt log of the big white oak down to the mill. It is about 120 years old, so from the age it began growing in the late 1800's and for here it is likely truly a second growth tree. The rings are tight in the first half century and then they explode in width in the late 50's/ early 60's... another harvest opened up light to the stand, the white oak was too small at that point to be taken. Over the years since the rings have again tightened up as the stand filled in again. The poplar I took just below it and the many dying locust, a short lived colonizer, have about 50 rings, they came in after that last harvest and is the third forest by my reckoning. Need to find shitake spores tonight and get them ordered, there was enough crown in the oak to make a mushroom farm. The smaller limbs of all the hardwoods will be cut to ~ 4', dried, and go to make charcoal. Oh well, I don't think that had anything to do with anything, but it was a fun day in the woods  :).