Engineering data for large timber

[Jim Timber]

I'm trying to figure out how to support a 24' wide floor in my new shop. The frame will be traditional heavy timber (8x8"), so I'd like to stick with timber instead of doing stick trusses. The problem I'm encountering is no one has any engineering data for this stuff, or at least none they're willing to share publicly.

I don't have any books on the subject yet, since I don't even have my mill built right now. But since it's cold outside and I have 3 months of winter remaining, I figured I'd start working out the new monitor barn's design.

Are there resources out there I've failed to dig up with google searching? Some kind of calculator that'll give me data I can plug into another software program for double chord truss design? Everything I've found, or has been suggested to me, is for 2x and maxes out at 12" widths. 2x12" oak maxes out at 19'6" for a joist.

I want to put two trusses across 24' on 10' centers and then string joists between them for holding the floor sheathing (or boards). One of these trusses will only support floor on one side, and the other side will be open to the center of the building. The other truss will hold joists on both sides and it's opposite side will be the outer wall of the building. If that makes sense.

Putting a steel I-beam in (I need two such members to support this floor) seems sacrilegious. I'd rather create a truss out of heavy timber to carry the load instead, but I'm not finding any way to run the numbers.

I'll be using clear red oak heart wood. I have plenty of trees to choose from, so getting good straight wood shouldn't be difficult.

I've suggested (2) 8x8"x24' cants coupled together with 6x6x8" blocking on 24" centers which would make a 24" tall truss. Does anyone here have an idea what the bending stress of such a member would be? Or where I could find some data on how to calculate it?

Any help would be greatly appreciated!

 

[kimosawboy]

For me a truss makes up a part of the roof yet it sounds like your talking in the floor???
Possible a ten cent stick diagram?

G Vavra

 

[Jim Timber]

This would be a floor truss to hang joists off of.

------------------------------------
I------I------I------I-----I-------I
------------------------------------ <- cross section where top and bottom chords are 8x8 and I's are M&T 6x6's for the web. I had to insert dashes between the web pieces because the forum software wouldn't allow a bunch of spaces.

An engineer over on TBN spoke up and said they couldn't come up with something to hold the roof on his place and had to do a LVL beam for a 28' span. With that, I'm beginning to think my concept ain't gonna fly and I'll have to go with an I-beam and wrap it with wood to make it blend in.

At least with structural steel, I can do the math easier and have little chance of gravity catching a mistake I made.

 

[M.R.]

Jim you might discard this right off.....
I've have trouble getting on the mindset
of what exactly you're asking.... dang tinnitus.
.
I entered in bci loading tables & this is what came up.
. http://www.bing.com/search?q=bci+loading+tables&PC=SMSM&FORM=MBDPSB
.
I use these in my own construction as they are dead true... compared to lumber/beams...
On some spans I've even glued & screwed 3/4 ply inside the web then another outside.
(4 thicknesses of 3/4 onto the BCI beam either full length
or the first 4-8' on each end...)
I'd have to boot the laptop up for calculation tables
to get links & its possible you'd might have the same.

 

[Jim Timber]

What I'm wondering is for cut timber's loaded as beams, and if they can be structured such as to make a truss which is more unique and visually appealing than a stick truss floor or glue laminated beam?

I think going with a traditional floor is going to win on this project, for cost and efficiency of erection. Maybe that'll change again in 5 months when I'm closer to building it, but for now I think I need to learn more about old-time construction engineering before trying to design the structure.

 

[moondoggie]

http://www.arboristsite.com/community/threads/structural-strength-ratings.83492/

Looks like useful info

 

[moondoggie]

http://www.fpl.fs.fed.us

Here too possibly

 

[moondoggie]

http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/fplgtr113.htm

This was in the 1st link somewhere. Think it takes you right to a specific handbook on what you are doing.

 

[moondoggie]

Chapters 3 and 4

 

[Mike Van]

Jim, faced with a similar problem 25 years ago, here's what I did - Mine was for a roof, I needed to span 18 ft so I could get 16 ft logs in. I used oak 2x12's I cut myself, 4 of them bolted every 2 ft, the entire length being 40 ft. There is a 14, an 18 and an 8 ft opening. The 18 in the middle, I've used a chain hoist on to pic a 24" 3 phase 30's planer on, wood furnaces, a 460 ci Ford engine with the transmission & transfer case, nothing has ever made it sag. Some winters 2 ft plus of snow sits on it. The opening on the left shows the header. Hope this helps?

 

[Mike Van]

Forgot to add - The headers are made up of 8, 10, 12 ft oak 2x12s, staggered so the ends are at least 2 ft apart. Good oak too, no big black knots. The building inspector wanted the inner & outer on the 18 ft span to be full length, that was all he asked for so I did it. Making 18 ft 2 x 12's on a mill that only does 16 ft 6 was a challenge best done then, when I was 40.

 

[Jim Timber]

The span charts list 19'6 as ok with a 2x12" red oak in structural select. It's going out another 20% that none of the charts or online calculators account for.

I've got a timber framing book coming from the library which many folks praise online. We'll see what it has to say about longer spans and go from there.

Thanks for the links to the FPL, MD. I had seen those before, but for some reason my searching didn't pull them up this time.

 

[Bwildered]

Just calculate the size of the beam needed from the following & mill it from a log with a chainsaw mill or whatever you have handy. If the member size is getting large then heart centred log with squared sides is an easier option.
Fanks

 

[Jim Timber]

My winter project is a bandsaw mill.

That chart is perfect though! Now I can use beam boy to check stuff easily. Thanks!

 

[Jim Timber]

Using those numbers, a 3,000# load centered on a 24' 12x12" beam will have .726" deflection with half an inch at just 8' from the ends. That's a whole lotta sag!

If I change it to a 50lb-ft distributed moment, the ends of the beam see 4000# load each, and the deflection shrinks to .182" or just shy of 3/16" and 150psi of bending stress in the middle. That seems low to me for PSI with 144 square inches per foot. I don't think my weight is high enough for what a floor might see.

Half the supported floor would be 144 square feet and should result in 7200# live load at 50lbs/sf. But since I'd have another half of the floor for the middle spans, this would possibly be acceptable if I had a 6' joist spacing, so a 12x12" beam is the functional equivalent to 3 trusses of 4" width only with a 1460# beam to hold up in the process (which I didn't calculate into the load).

Does that sound right?

 

[Bwildered]

Using those numbers, a 3,000# load centered on a 24' 12x12" beam will have .726" deflection with half an inch at just 8' from the ends. That's a whole lotta sag!

If I change it to a 50lb-ft distributed moment, the ends of the beam see 4000# load each, and the deflection shrinks to .182" or just shy of 3/16" and 150psi of bending stress in the middle. That seems low to me for PSI with 144 square inches per foot. I don't think my weight is high enough for what a floor might see.

Half the supported floor would be 144 square feet and should result in 7200# live load at 50lbs/sf. But since I'd have another half of the floor for the middle spans, this would possibly be acceptable if I had a 6' joist spacing, so a 12x12" beam is the functional equivalent to 3 trusses of 4" width only with a 1460# beam to hold up in the process (which I didn't calculate into the load).

Does that sound right?

I only understand metric units so it's all japanese to me, we use a guide for loads which will give the loads in Kpa & Kn as shown above

Tanks

 

[Mad Professor]

They did this hundreds of years ago in barns. It was called a swing beam that allowed wagons to turn inside the span of the barn. An old mastercraftsman, Richard Babcock, documented some of these structures and restored them. Richard has passed but his work lives on. I do not have a picture handy but it was German style barn that was published in one of his works.

Google Bacbcock, Old barns in the new world , .The Barns at Wolftrap, ......

 

[KiwiBro]

Glulam beams can look good, Jim.
If visible glue lines are not an option, then how about a 12x4 (or wider) with a 1 x 10" centre rebate and a structural ply stiffener glued in there?
Or, perhaps the roof beams can handle the load of a tension wire dropped down to the mid-span of the floor beams, but then there'd be a wire/s in the way forever more.
Do you have the height to go to taller beams?

 

[Jim Timber]

I've got all the height in the world if I don't use solid center posts (floor to ceiling of second story). I think I'll be building OSB laminated trusses for the floor joists and put a steel ceiling in the bay below. I have a white steel ceiling in my house's garage (the shop is sheetrock - what a pain!) and I like it a lot.

After all, it's a shop and the rest of the structure will be cool even if this floor isn't.