New Garage Pole Barn 40 x 64 x 12

[bugstruck]

I still don't see why you would need these along with gable braces. I guess I can't see the gable wall deflecting at all with a properly built gable brace.

Typically one or the other is done around here.

Well I guess I just didn't convey it to well. It does make a notable difference if all planes (top chord planes and bottom chord plane) have their own integrity and something to provide shear resistance before you connect them. The top chord roof planes do on all roofs. All the gable brace does is lock the different planes together and impart the roof plane strength back down to the bottom chord plane (in an unsheathed bottom chord condition). I'm talking pole barn with a full gable truss. Much less important but still useful on a stick build gable endwall.

Most think of this backwards when they look at a gable brace in a pole barn application and it's understandable. Not saying that's how you see it buy many do.

Take if from a framer, they work.

 

[Steve C]

Ties the outermost corners together in the plane of the bottom chords. In a large pole or framed structure, presumably without interior walls like a home which would provide added shear against lateral wind loading of the walls/gables, the corner braces stiffen the gables againt unusual pressures. Better way to explain it is that if you pushed on the center (bottom) of one gable truss with enough force you could deform the opposite gable in the same direction. Granted, you eventually have to overcome the membrane resistance of the roof (but it's not in that plane) and deform that too.... but when you get larger expanses of gable and end wall exposed to wind, no membrane on the bottom chords (as drywall ceilings are in a home), the structure is much more vulnerable wind to loading. Those corner braces are fast, cheap, and easy. You would have to run calculations on any particular structure to reach a real conclusion but a large span truss pole barn with corner braces may take say another 20 or 30 MPH of wind (on gable) before anything starts to deflect. We are talking larger wind speeds and loads. If it never gets over 60 MPH sustained it problably is not an issue in that rough example. But at 75-80 its potentially a problem. I never built a truss roof house without corner braces (except attic trusses) and they have all kinds of ancillary supports a pole barn doesn't. Haven't framed in my home state of Maryland in quite awhile but you had to have those corner braces in every conventional trussed roof home in the late 70's and early 80's. Not sure what other jurisdictions require.

Large truss center to center spacing on pole barns doesn't help things out either as there are fewer connection points to the purlins or sheathed roof membrane meaning that plane is a bit weaker to start.

Smaller structures are not the same issue as there isn't enough surface area and unbraced expanse to worry about it. Frankly, neither is the average house gable once the drywall is up.

My trusses are on 24 inch centers and the roof deck is sheathed with 1/2" OSB. I have 5 longitudinal braces that run the full length of the barn that feed the horizontal forces directly into the vertical poles at the far end of the barn at the quarter points of the lower chord. The poles are attached to the top of the trusses at the roof sheathing and burried in the ground 4 feet so a horizontal force on the outside wall at the bottom chord of the truss will try to bend the 6 x 6 vertical pole and will have to deform the roof sheathing because the top of the pole will carry that force up to the top chord of the truss, and that is braced with the roof sheathing. Is this strong enough or do I need the braces shown in red on my picture?

 

[Duffster]

Well I guess I just didn't convey it to well. It does make a notable difference if all planes (top chord planes and bottom chord plane) have their own integrity and something to provide shear resistance before you connect them. The top chord roof planes do on all roofs. All the gable brace does is lock the different planes together and impart the roof plane strength back down to the bottom chord plane (in an unsheathed bottom chord condition). I'm talking pole barn with a full gable truss. Much less important but still useful on a stick build gable endwall.

Most think of this backwards when they look at a gable brace in a pole barn application and it's understandable. Not saying that's how you see it buy many do.

Take if from a framer, they work.

Like in the drawings below?

 

[bugstruck]

Steve,

First off your structure is superior for strength to the one I was looking at and discussing. Not that the other isn't fine with a little tweaking, you just have tight truss spacing at 24" and direct applied sheathing so that roof plane has excellent shear capability and superior resistance to uplift. Somewhat unusual for a pole barn. Now I'm going to appear to countermand myself but it's because what I'm seeing is different. You would be OK using just the longitudinals and some gable braces unless you are in a high wind area IMO. That roof has the stength to impart back down to the bottom chord plane in your application and hold the gables. Also your spans aren't too huge. There is another structural benefit to the diagonals though I'll spare us for this post other than to say they add some additional rack strength to the box and your wall height makes me think I'd still do them. Duffster's way is fine on this one though.

Should you want to use the diagonals on the bottom chords for added strength.....The (RED) braces in your photo are in the correct general orientation and can be on top of the bottom chords (where I generally put them). However, they don't need to make the center point on the gable (shouldn't really) and and they sure don't need to run all the way to the center point of the structure. When you top mount them you have to clear compression and tension members in the trusses so your placement will be dictated and limited by that. In your application you could bottom mount too and put them excactly where you choose. Ideally they would tie into the gable near the 2nd and 4th longitudinal braces but even that isn't critical. Generally you want them to break the gable into three near equal spaces and you just angle them back to the exterior long wall at something roughly in the 45 degree range (ain't critical we are just making a triangle). Lets say a 14' diagonal 2 x 4 gets you about 10' over on the gable and 10' back on the long wall. That would be great for spans in the 30' range. Wider just needs a little longer diagonal and you can break the diagonal up into two side by side lengths on very large structures but you need some overlap (they can overlap side by side if well nailed to two or more trusses and to one another at the overlap). By the way, that is one nice looking structure.

 

[Steve C]

Steve,

First off your structure is superior for strength to the one I was looking at and discussing. Not that the other isn't fine with a little tweaking, you just have tight truss spacing at 24" and direct applied sheathing so that roof plane has excellent shear capability and superior resistance to uplift. Somewhat unusual for a pole barn. Now I'm going to appear to countermand myself but it's because what I'm seeing is different. You would be OK using just the longitudinals and some gable braces unless you are in a high wind area IMO. That roof has the stength to impart back down to the bottom chord plane in your application and hold the gables. Also your spans aren't too huge. There is another structural benefit to the diagonals though I'll spare us for this post other than to say they add some additional rack strength to the box and your wall height makes me think I'd still do them. Duffster's way is fine on this one though.

Should you want to use the diagonals on the bottom chords for added strength.....The (RED) braces in your photo are in the correct general orientation and can be on top of the bottom chords (where I generally put them). However, they don't need to make the center point on the gable (shouldn't really) and and they sure don't need to run all the way to the center point of the structure. When you top mount them you have to clear compression and tension members in the trusses so your placement will be dictated and limited by that. In your application you could bottom mount too and put them excactly where you choose. Ideally they would tie into the gable near the 2nd and 4th longitudinal braces but even that isn't critical. Generally you want them to break the gable into three near equal spaces and you just angle them back to the exterior long wall at something roughly in the 45 degree range (ain't critical we are just making a triangle). Lets say a 14' diagonal 2 x 4 gets you about 10' over on the gable and 10' back on the long wall. That would be great for spans in the 30' range. Wider just needs a little longer diagonal and you can break the diagonal up into two side by side lengths on very large structures but you need some overlap (they can overlap side by side if well nailed to two or more trusses and to one another at the overlap). By the way, that is one nice looking structure.

Thank you for the information. My barn is 40 x 60 x 14. I am planning to install an OSB ceiling in the future, that should stiffen things up a lot. Meanwhile I think I will add the diagonal on top of the trusses as you suggested. I have some rather long 2x4's that were used as temporary wall bracing that will be ideal for that application.

They are already paid for and just taking up space in my other barn

Then I am going to build a 7 foot tall mezzanine and storage deck 12 foot wide and a full 60 foot long along the south wall. so that deck will stiffen that wall considerably.

 

[bugstruck]

Isn't spare wood great stuff? That OSB on the ceiling and the mezzanine will do just as you said, super strong elements. Keep up the great work and send some pictures along the way.

 

[yooperdave]

The continuous longitudinal braces are specified by the truss designer.

You should verify with the shop drawing that they are installed in the right place.

The braces are required to:

1. Limit the unbraced length for compression members (some of the webs) to prevent buckling.
2. Limit the unbraced length for bending members (bottom chord) in order to structurally justify the interaction (bending/tension) ratio by using higher allowable stresses. Depending on load case - say wind, the bottom chord might go into compression, and would (also) require bracing to prevent buckling.

Hope this helps.

Yooper Dave

 

[hcallaway]

The plans are suppose to be back from the PE today. I know that I am going to add additional bracing if they don't do it. I would imagine you cannot have too much. The picture with the red markings really helped understanding what you guys were saying.
I did get out to the job site today and yesterday. I was able to move some dirt and some mud!!!! I almost buried the New Holland last week in the woods. It was down on the axles it was so wet. The FEL worked me out six inches at a time.

 

[Steve C]

The plans are suppose to be back from the PE today. I know that I am going to add additional bracing if they don't do it. I would imagine you cannot have too much. The picture with the red markings really helped understanding what you guys were saying.
I did get out to the job site today and yesterday. I was able to move some dirt and some mud!!!! I almost buried the New Holland last week in the woods. It was down on the axles it was so wet. The FEL worked me out six inches at a time.

based on what bugstruck said I think this what it wants to look like, breaking the gable into 3 equal parts.... Your dimensions will be different of course if you span is different..not real critical

 

[hcallaway]

I called the gravel guy to see about getting a few loads for my road. He is a young kid so I am trying to send some business his way. His truck has been down for 2 weeks, but with the rain it really has been too wet to do much of anything. The sun has come out and more importantly the rain is going to stay away for most of the next 10 days. Since I have saved some money in other areas, I have rationalized why I need another trailer. (We now have a car trailer, 8 x 12 Feather Lite Aluminum, 3 rail MC, 7 x 12 enclosed and a 7 x 14 utility.)
I always wanted a dump trailer and now I will pick it up on Monday in WV.
What do you think? $3899 plus $100 for a spare tire.