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Beam or truss

Started by WH_Conley, February 15, 2005, 11:19:07 PM

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WH_Conley

I am getting ready to build a new mill shed and was wondering if I could laminate a beam of say 1 1/2 x 12 poplar to make a 30 ft beam, stagger joints and through bolt on each side of joint and use single pitch rafters or should I go with trusses instead? Only 12 ft across end.
Bill

Buzz-sawyer

Wh
If I understand right, you are building a shed 12 wide and 30 long?
If thats so ...you can use a single 2x12 as the ridge board and lenghten it with plywood gussets on both sides of the butt joint were you add extra lenght ...just put bout 12 nails on both sides., then us collar ties on the raftersI wouldnt bother to build a truss for a building that size.
    HEAR THAT BLADE SING!

WH_Conley

Correct on size, but the 30 ft needs to be clear span
Bill

Jim_Rogers

What's the snow load per square foot for your area?
Is the total distance of unsupported beam truly 30' or will you have some braces coming up from the ends posts to the 30' beam?
Are you going to have just four posts or will the opposite wall of the 30' beam have more posts?
How many layers of 1 1/2" x 12"?
Why only 1 1/2" thick, why not thicker?
By single pitch rafters do you mean a shed roof?
If so is this 30' beam the ridge and the other side of the shed the eave?
Or is this a gable roof?
What will be the roofing material?
Board with shingles? or tin roof?
There is a lot of information needed to understand and give you a good guess......
Jim Rogers
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

WH_Conley

Don't know about snow load charts, most ever had in any of the old timers memory was 30 inches a few years ago.
Would have knee braces coming off the ends, total clear about 24 ft.
4 posts.
how many layers is subject to advice I get, at least 4.
1 1/2 to get as many layers as possible as they will have to be spliced.
Shed roof.
Beam on each side, one higher than the other.
2x4 rafters, 1x6 sheathing boards on 16" center with metal roofing.

Just wondering which would be strongest, single pitch would be easier to construct, but I don't want it falling down.
Bill

Buzz-sawyer

I didnt realize this was on timber frame forum....I have been buildin COVENTIONAL frame structures for a few decades I will let Jim answer ya ;)
One thing to remember most houses are bui;t with spans like that  :)
WH
    HEAR THAT BLADE SING!

WH_Conley

I have built a bunch of houses longer span, but there was somethin in the middle, unles using trusses. The beam idea is new to me, that's the reason for askin, curious about beam. All input appreciated.
Bill

Jim_Rogers

Bill:
You need to find out the snow load per square foot........
Go to the coffee shop and ask a carpenter......
Call your building inspector.......
Call a neighboring town's building inspector if you don't want to call yours.....
Call a lumber yard and ask them.......
Go to the state website and look it up under building codes.....
Find out some how.....
Around my area it's 35 lbs.
Not far from here it's 60.......
This can make a big difference in load on the roof.
If you're going with 2x4 rafters what type of wood?
Seems a little small for rafters.......
Are the 1x6 just nailers for the tin roofing?
Are they going to be 16" oc as purlins?

I have some pictures of a saw shed where they used floor trusses to span the open side distance.
I'll try and find them later today, after dark, and post them for you to see.
A 30' floor truss would work......
If a built up beam doesn't.
Jim Rogers
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

WH_Conley

Jim, I'll try to find out in around the first of the week, just had whole bunch of mechanic and welding dumped on me, nothing all winterm with a heated garage to work in, now it all comes at once. will answer what I can now.

2x4, rafters to span the 12 ft, 12 in center
1x6 just nailers for metal roofing, 16"

Stopped at a lumber yard that had the engineered floor joists, the ones with 1x4 and plywood, asked about load and span, only one that knew anything was a kid, he said 24 ft was as far as they would span, asked why they had 40 footers on the lot, couldn't tell me, I'm going somewhere else, had no confidence.

Are we talking about the same, floor truss and engineered floor joist? Thats what the stores around here call them, I never did use them myself. They have not been used very much around here til recently.

Might be a couple of days before I get back on here, Thanks for all the help.
Bill

Jim_Rogers

Bill:
An engineered floor joist is a joist that has been made up of some composite board and two pieces of solid wood. Usually shaped like an "I" beam.
A floor truss is a truss that is flat on the top not pointed like a roof truss.





If you go to my album you can see more photos of this saw shed.

I don't remember how wide or how long it is, but the floor trusses set into a notch cut on the outside of the pole and are bolted to the post.
The rafters are quite small but with the steep roof pitch and tin roof the snow load duration is short.
What that means is the snow doesn't stay on the roof very long and so the load rating is lower, so that you can use smaller pieces of wood to create the roof structure.
What I'm suggesting to you is to use a floor truss similar to these.
Then you will or can span long distances.
I hope this is useful to you in your design.
Jim Rogers
Jim Rogers Sawmill
Jim Rogers Timber Designs
Georgetown, MA
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

WH_Conley

That's the application I was looking for, Thanks Jim, answers my questions.
Bill

Don P


Do keep in mind though, although a floor truss may be sized to span 30 feet it was meant to carry just 16-24 inches of width, not 6 feet. Although you will likely be just fine a stock floor truss is not a universal solution to this problem. A truss of some sort is probably the best solution though.

Look at the depth of the 30' floor truss. That depth is showing the size of beam required to get the stresses into a safe zone for wood.
I just used some 24" deep floor trusses, no girder combination of 2x12s would have given the strength and stiffness required at the span we had, it took depth. In beam formulas, width of beam times depth cubed is part of the equation. Depth is heavily favored.

In other words at a given span a certain depth is generally more efficient. To carry it to extremes to help visualize it... a 3/4x3/4 strip spanning 30 ' will fail, adding more strips alongside of the strip will not improve the situation, adding more strips above and below will have a marked effect. A 2x12 or a bunch of 2x12s at 30' out will not be deep enough for the span. A 6x12 at 30' long under a 5400 lb load will sag about 4 inches and likely fail. a 3.5 x 24x30' under the same load will sag about 3/4". A 12x12 will perform almost as well as a 3.5x22 in that case. "Deeper is cheaper"

I've used the TJI's in full 40' length...but crossing over several interior support walls  ;).

Jim_Rogers

Good advice Don P.
All loads need to be figured on and calculations need to be done, correctly to determine what size floor truss could be used.
You may have to gang up several to get the load carrying capacity or as Don states make them taller.
This is important to figure it all out first.........
Jim Rogers
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

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