building a pole barn.

[cgp]

with pipe.
Outside to outside walls are 30 ft. wide.
40ft. deep total.
Building truss's out of pipe.
If rise is 6.3' and from center to outside wall is 15'(5/12); How much is length of rafter/pipe with 2ft.overhang?
And what would the angle be at crown for cut?
thanks

[Don_P]

I've attached a picture of the triangle showing the angles and ratios of side lengths. I set the rafter to 1 but you could set the run to 1 if its easier to think about.
Anyway if the bottom leg is 15' then 15/.923=16.25'... its easier for me to think in inches here, so 180"/.923=195"
195"x.384=74.88" rise
2'level ohang..204"/.923=221" OAL on the rafter, the 67.4* is the plumb cut at the peak, slot the members and insert a plate?

edit, I put up another pic with the ratios set in green so that the run is 1, the rafter is 1.083 units for every unit of run and the rise is .416 units for every unit of run length. Its all the same 5/12/13 triangle just different ways of looking at the proportions.

[cgp]

Don,please bare with me.
If 5 is 74.88" and
if 12 is 180".
How many inches is 13 ?( without 24" overhang)
thanks
cliff

[Don_P]

195"
for every inch of horizontal run (180") the rafter length is 1.083" (180x1.083=195")
Here's a calc I made that might double check too;
http://windyhilllogworks.com/Calcs/rftllclc.htm

[cgp]

Your too good.
Thanks a million.
I'll get back later.
Cliff

[cgp]

How do I insert an image?
Or send me your e-mail and you can post it.
thanks

[Don_P]

Click your name and check your profile page :)

[cgp]

thanks alot.
Wandered if you could figure these 2 braces for me.
I'm making all of the truss out of 2 3/8o.d. oil field pipe.
Also if you could figure for 49" rise and 180" run? (for my son-n-law)
thanks again
Cliff P

[Don_P]

Man I hate it when the computer eats a long post.
attached is a pic of a truss, notice that its made up of all triangulr sections. Triangles can be pinned together and do not distort. Pin the corners of a square or any 4 or more sided structure, push on one side and it distorts. So that's the definition of a truss, triangles. Notice trusses, high tension towers, highway sign trusses, etc, all triangles.
I've attached a sketch of a simple truss done on an online truss analysis program.
http://www.jhu.edu/~virtlab/bridge/truss.htm
I did it quick and lightly loaded it to show how the stresses run in the members. Notice I divided the bottom chord into thirds and the top chords in half. This is pretty typical, if the loads exceed the pipe strength the next thing would be to divide the top chord into thirds and the bottom into fourths, etc until the members can handle the loads.

Questions;
Where are you, or more important what is your snow load in pounds per square foot?
Wind?
Desired truss spacing?
Is this schedule 40-.154 thick, 80-.218 thick, or 2x-.436 thick?

I'm not an engineer, so this is worth exactly what you're paying, it should be reviewed by one but it looks like it would be interesting to figure if you don't mind.

[cgp]

D;
This one's for my son-n-law.
It's got to be done this way because of the poles he's got set.
Was hoping you could fill in the unknown sides on sketch.
thanks
cliff
Liberty, Mississippi

[Don_P]

Boy that sounds familiar, I'd swear I know someone named Marcel around there. Well we don't need to worry about snow load.

As drawn, it is not structural, the internal webs are wrong. If you add the one in red in addition to the others it will work but is not the best way to lay it out, you're making the ceiling stronger than the rafters. Also the top chord 93" lengths are incorrect or the 49" is wrong, the lengths of the 3 sides don't form a right triangle.

You're getting me turned around here, the run has gone from 180 to 168 (3x56"). I'm getting lost. Let's work on one truss, what are the numbers we can't change? I'm assuming the posts are set at 28' wide outside to outside and it needs to be a 49" tall? Or do you want it to be 4/12? I'm assuming the internal braces can be put where they work the best? Is there anything hanging from the ceiling or is it just exposed truss?

[cgp]

Yea; they named the hwy that comes into town from that way; "Jerry clower Memorial Hwy".even got a museum at his place on Amazing Grace Lane.

Anyway; I'm sorry for the confusion.
i can do mine later.
Son n laws middle pole is 49inches above his 8 foot mark.So lets just let that be the rise for the crown.
I'm gonna build it piece by piece.Tack it all in place and then weld it out.
I've already got a saddle wrapparound for the 2 3/8 pipe.
Just fell free to add the braces as u wish.
i don't know the correct angles to make the cuts on braces and at crown; but thats ok .
thanks
cliff

[Don_P]

atan (180/49)=15.22 degrees, that's the roof slope and the plumb angle at the peak.

Now the fog is clearing, how far apart are the posts from truss to truss? Or to say it another way, what is the truss spacing?

My Dad made a couple of trips down below you after the storm, one was to Pearlington for a month or so. Wind is going to be an issue, how bad did you all get torn up?

[cgp]

i live on 10 acres that had a lot of very large pine trees.What the strom did not get ;the bugs got the rest later; so i ha d to cut them all.
There are 3 poles across the front; 3 in the middle at 20' and 3 across the back at 40'. Thats where each of the trusss' are going. I'm gonna use some perlings to span everything .( don't know what size yet)
Later i will put some angle or tubing all the way around at 8 ft. then drop a support post ;(2 7/8 " pipe at every 10ft of run; down sides and in gaps at back and concrete in.I'm using old tin i took off an old old feed mill.
From the center of the truss to the outside of wall will be 15 foot.

[Don_P]

Gotcha, there are 3 sets of trusses, 20' apart. The middle one is taking the heaviest load so lets design them all the same but were designing to take the load halfway to each endwall so 20' wide x 15' is bearing on each, 300 square feet. Minimum design load is 20 lbs per square foot, 300sf x 20 psf= 6000 lbs on the truss.

The purlins are 20' long so they are going to be putting quite a load on the point where each one bears on the truss. I think we had better make the braces come up under and reinforce each purlin.

so the next question is how many purlins... how far can the tin span between purlins?

[cgp]

Sounds good.
8 purlins in all.
One at top; then 5'-2" to the center of next one ; then 5'-2" to center of next one ; then 5'-2" to center of next one over the outside wall.
Here's a pic of top view.

[cgp]

here it is

[Don_P]

Allright, this looks like its gonna work.

This is a pic of the truss analysis. Add a zero to the end of every number. On the top chord I've hung a 2,000 lb load from each purlin/ brace node location (in black). The highest compression load is 8650 lbs in a 5' section of the top chord. Dividing that length by the radius of gyration for a 2" schedule 40 pipe and checking the allowable load per square inch for that type of member and multiplying by the area of the pipe, the allowable buckling stress for that most stressed section of the truss would be 16,500 lbs, we're running 8650 lbs, were good. By putting the purlin over a brace there is no bending load in the top chord its pure compression, do not put a purlin or load anywhere other than over a brace point or we'll have combined bending stress and buckling stress! 2" is pretty small and I couldn't put much load anywhere else without the combined compression and bending getting it into trouble. If you pull an engine do it at a braced point :D

Anyway it looks like the design works, now we gotta draw the thing... tomorrow :) I think the easiest way is to slot the ends of sections of pipe, weld flat plate to the top and bottom chord pipe and slide the slotted brace pipes over the flat, then weld, it'll give some slop room, be easy to bring several pieces together in one spot and give lots of weld length... I'm thinking something like 1/2x 3" flat stock off the top of my head, whatcha think?

[cgp]

Sounds good to me.You talkin about not making fitt cuts on pipe ends and cutting the ends square or fitting the ends plus slotting?
I'll know today for sure if the truss pipe is 2 3/8 od.It may turn out to be 2 7/8 od which is the size of my poles.Don't have it here right now.Also might have to go with 3/8 x 3 1/2 flat.
Thinking about using 8" purlin's . idontno

[Don_P]

I'm just kicking around ideas, trying to make it as easy as possible but give good connections, you probably know more than I do there.
I played around with some scrap this evening just trying a mock up. This would be the peak, the 49" riser is on the left, top chord on top, brace chopped and slid onto the flat stock. It would all get fully welded.

(swung 37-1/2 degrees to bisect the top angle...90*-15.22*= 74.78*. divide 74.78 in half=37.39*)

You know, thinking about it, if the 49 is going to a square post it could be a piece of angle.

[cgp]

yea. Looks great.

[cgp]

The 49" is allready there Don.
Inotherwords its an extension of the center pole( s) which is in the ground now.
Total center pole height is 12'-1" .
I hope I'm not misunderstanding ya.

[Don_P]

I'm understanding that the posts are just 2-7/8 od pipe? I'm worried that isn't much in the wind. I started thinking about how ancient timberframe barns were done with "passing braces". In the sketch the brace is continuous from low on the post up to the top chord (rafter). The bottom chord is interrupted and tied to each side of the brace. This gives it a lot more sway bracing.

So really there's no need for the miter on the 49/top chord I welded up earlier, the post top could be slotted and a plate goes thru it then the top chord is chopped to a 15* angle and slotted onto the plate and the brace comes up under and is slotted onto the plate. It doesn't need a seperate 49" piece, like you say, its there.

Had a chance to measure the pipe size?

[cgp]

Sounds great.I had'nt had a chance to measure pipe. It's under a barn about 20 miles away. When I go to get pipe I'd like to make (one time) cuts if I can.At least the straight cuts.
I do understand how to slot and do the peak part; but how would I do the other bracing tie in's?I guess just weld flats to the run and slope pieces and slot braces??????
thanks again

[Don_P]

Exactly, the slots are only on the ends of pieces, in the run just weld plate standing up on the side. I can dig up allowable strength per inch of weld but basically make the plate long enough that the weld to the side is strong enough for the stresses. If you weld good and get good penetration that doesn't take much, you'l be getting thousands per inch of weld.

[cgp]

OK.
Can you give me a reference point for each flat. Possibly a end to center and then center to center? Basiclly tell me where to put them? ha
thanks
cp

[cgp]

Pipe size will be 2 3/8" OD for all of truss.

[Don_P]

See how this looks, it should be cut lengths for the parts. Top chord is the only thing angled, 15* everything else is square to square. Some of the intersctions might look strange at first glence but what you try to do in a truss is have the centerlines of the parts all converge at a point so you create a "pin" type rotation in the joint rather than an eccentric. Anyway, see if this part come up readable.

[cgp]

I like the layout tools you use.
Had a few ??????

[Don_P]

The top chord on the posts is fine. The brace from the post is one way I'm trying to come up with to make the posts substantial enough. I'm afarid they're too small to take much more than a breeze. Imagine a pickup truck perched on top of the post and then attach a sail (the roof and wall) to the post. That's about what this is doing to the posts. In the endwalls this is pretty much buried in the wall so it only occurs in the middle bent where it gets in the way, and that is the most heavily loaded bent. It could be a pair of posts with plate or zigzag tubes between the two to make basically a vertical truss.

That was done on Sketchup, its a free download program that is pretty amazing for drawing and dimensioning things. I can tell from the type of stuff you like to do, you need it, it is a real timesaver, easy to learn with their tutorials online.
http://sketchup.google.com/

[cgp]

Would this work only on front left corner?All others could be like sketch.
I'm parking truck there

[Don_P]

I'd say if there is a good bit of sheathing on the other side that it would be well enough braced. I'd put a short strut between the top and bottom chords over the inner post just to make it bend both if it does try to tip.

The 2' overhang is ok on that truss but its mighty far to the next truss and I doubt it could hold very much without bending. The shorter the overhang the better windwise. What are you planning on spanning from there to the next truss with?

[cgp]

8" purlins ; 2 1/2 " tall; 14 gauge; 20' long.
The first run centered over outside wall. The next at about 5' and the next about 10' and the top one; next to the crown.

[Don_P]

The closest I came to being an engineer is running my cousin's train set one Christmas but I think this is it. I drew lines to measure to for plate placement that are centerlines and crossing points of the centerlines in places, if that makes sense. The pipe lengths are actual.
If you hang anything on that overhang I'd brace it back to the post. You'll have to satisfy yourself on the purlin strength at that span, I've got no idea. I think it's pretty well braced in the plane shown, you'll need to figure out bracing the long way of the building, diagonals between bents and trusses maybe.

[cgp]

You've been a big help Don.
Could not have done it without you.
Now i've got to get to work.
I'll post later

[Don_P]

Quite welcome, I learned a good bit playing with it, now its your turn, look forward to seeing pictures :)

[Don_P]

I came across this plan for a steel pipe truss today;
http://www.lsuagcenter.com/NR/rdonlyres/C5D22C7D-C513-40A6-A10F-0ADE76EA3374/12242/441140FTSteelPipeTruss412pitch.pdf

[macrylinda1]

thanks alot.
Wandered if you could figure these 2 braces for me.
I'm making all of the truss out of 2 3/8o.d. oil field pipe.
Also if you could figure for 49" rise and 180" run? (for my son-n-law)
thanks again
Cliff P

Man I hate it when the computer eats a long post.
attached is a pic of a truss, notice that its made up of all triangulr sections. Triangles can be pinned together and do not distort. Pin the corners of a square or any 4 or more sided structure, push on one side and it distorts. So that's the definition of a truss, triangles. Notice trusses, high tension towers, highway sign trusses, etc, all triangles.