Pole barn with ridge beam

[MER3]

Father in law has asked for some advice regarding a project. He is building a barn that will measure 48'x30' with a roof supported by a ridge beam and a 4/12 slope. He wants to support the ridge beam every 16' but would like to not have any columns in the interior. He wants to run a post down from the ridge beam to an I beam spanning the 30' dimension and support the I beam on the edge of the building.

When he told me this my first concern was the unbraced length the i beam. A beam can be sized to run that length without needing much in the way of bracing. We are in VA so the snow loads aren't too high. The second concern I have is the inevitable splice. My bigger concern with a project like this is that as you start chasing loads you realize nothing calcs out anywhere.

So is my guy feeling right on this?

 

[Wallache]

Since head room isn't an issue, why not switch to trusses? Simpler and cheaper than all that steel and ridge beams.

 

[MER3]

Probably could have done that but we are past that phase of the process.

 

[BAretired]

When he told me this my first concern was the unbraced length the i beam. A beam can be sized to run that length without needing much in the way of bracing. We are in VA so the snow loads aren't too high. The second concern I have is the inevitable splice. My bigger concern with a project like this is that as you start chasing loads you realize nothing calcs out anywhere.

* So there would be two beams 16 feet apart, right? Add bracing as required and design the beams.
* What inevitable splice? Aren't the beams in one piece?
* I can find no reason why everything should not calc out.

BA

 

[Once20036]

If it were my father-in-law, I'd send him back to the guy that did the original design.
Why modify something that someone else designed when it's not even built yet?

 

[dhengr]

Hardworker87:
I agree with Wallache, use trusses. It is almost never to late to do it right in the first place, since you will more than likely be redoing it (correctly) at some point in the not to distant future. And, then you will be blamed for not telling the father-in-law of the errors of his ways at that time. And, you’ll get blamed for the cost of the fix or redo also. He may have produced the most beautiful and nicest daughter in the whole world, but he doesn’t seem to know very much about structures, or what’s ugly on that account. Those buildings are loose as a goose in the best of designs, and without roof trusses and a good strong roof sheathing planes (diaphragms), they are a house of cards waiting to fall down. Don’t forget roof uplift and lateral loadings. His roof framing scheme has about 60% of the roof load going to two posts at the gable ends, a fairly sizable concentrated load on a long post, whatever its size and foundation is; rather than to seven shorter posts on each side of the bldg. You haven’t given many of the important details, but your comment..., “ My bigger concern with a project like this is that as you start chasing loads you realize nothing calcs out anywhere.” pretty well sums up what I’m imagining so far. You might be able to use a wooden girder truss down the middle of the bldg. Then provide good roof sheathing diaphragms and brace the hell out of the gable ends.

 

[BAretired]

I see nothing wrong with the proposed framing from a structural point of view but must admit that trusses would have been my first choice. I still don't know where the "inevitable splice" occurs.

BA

 

[BAretired]

Each post at the gable end would carry an area of 8x15 = 120 square feet of roof load. Each I beam would carry a concentrated load equivalent to 240 square feet of roof applied at midspan. If snow plus dead load = 40 psf, each beam would have a point load of 9,600# at midspan and a moment of 72'k which seems doable.

BA

 

[MER3]

The splice would come from not being able to get a 30' I beam in one piece. I came up with some loads already and they are in the range that BAretired posted. A 30 foot beam of the right size, even without any bracing, should be able to do it. The only way I see to brace it is to take some lumber and bolt it to the top flange of the beam and use that to send braces back in either direction to the ridge beam, but I don't see that doing but so much to help.

 

[BAretired]

You should be able to get 30 foot long WF beams at just about any fabrication shop. There are several different ways to brace them against lateral torsional buckling. The simplest is to use a horizontal member between top flanges, then add a V brace between the two posts to prevent translation of the flanges.

If delivery of steel beams is a problem, how about using a pair of glulam beams or timber trusses instead?

BA