Post & Beam Sizing Question

slvr98svt · Apr 7, 2014

Hey guys I have been gathering some info from resources online and trying to get an idea of what I want for a monitor style barn. I drew up a quick diagram with sizes that I am looking for help on. The 10' width will be open "lean-to's", with the 12' sections being stalls on one side and storage on the other and then obviously a 16' open center.

I have looked up a couple of the online calculators and tried to use them to size the beams and posts but, I are dumb when it comes to the names and trying to decide if its actually what I am calculating. So with that, I am looking at storing hay in the loft but want to make sure it is safe to do so. This will all be rough cut, dried lumber, cut to actual size. There will be 5 sections totaling a length of 48'. So with 8x8 posts for the aisle, and 8x10 "headers" spanning the 16' with corner braces. If I use 2x10's running the "length" of the building on 12 or 16" center's (connecting the 8x10 together) what would floor load bearing being?

Thanks guys, just napkin sketches right now.
-Matt

rtimgray · Apr 8, 2014

Looking at some old span/loading tables, a 12' long 2x10 (syp or fir) will support approximately 1,425 pounds. The old book that it's in says that if you are using green, rough sawn lumber and it is actually cut to 2" x 10" instead of 1 1/2" x 9 1/4", it will still be a little weaker (depending on species) while it is green, but after it dries it will likely be stronger. Saying all that to say this: The book says using SYP or fir as estimation tools will be fairly accurate.

Anyway, this would mean that if you place a 2x10 on 12" centers and it's 12' long, it's responsible for supporting 12 square feet of floor space, so the distributed load over the span would balance to 118.75 PSF. If you go 16" oc, you'll be carrying about 16 square feet, which drops your PSF rating to about 89.

Our square hay bales are about 20" wide x 40" long x 16" tall, and weigh about 60 lbs, although this varies somewhat. So the footprint of a single bale takes up 5.56 sq. ft. and delivers a load of about 10.67 PSF. Of course, I'm sure you're going to stack the hay more than 1 bale high, so it looks like, in general terms, if you space the 2 x 10s on 16" centers, you could stack the 8 bales high (over 10' tall in my case).

You guys feel free to check my math. I made a mistake once before when I was a little kid and didn't know what I was doing.

Good luck and take care.

KennyG · Apr 8, 2014

Those numbers look good based on my tables. Keep in mind that is for distributed load. Point load is only half. Make sure you block the joists well so they don't twist.

slvr98svt · Apr 8, 2014

Awesome guys that is what I am looking for. I think I will go with 12" center's just to hopefully be on the safe side, and this would all be after allowing it to dry up for a couple months.

KennyG as far as blocking, you are talking about "x" in between the joists along the 12" length correct? Are we talking 1 in the middle, 1 every 3-4 feet? I want to make it as safe as possible so probably the more the better.

Thanks,
-Matt

rtimgray · Apr 8, 2014

I know you asked Kenny, but I think it's pretty typical to put them in the middle of the span, especially for a 12' span. I've always used solid blocking, but I think the "x"s would probably work just about as well.

The other thing to consider is how much your 8x10 headers will hold - again, my old book shows an 8x10 on a 16' span will hold about 4,300 lbs. I'm not sure how much of the span you will cut out with the corner braces - if the span goes down to about 12', the loading will go up to about 6,000 lbs, give or take a little. If the bays of the barn are 12', then each header will have to support about 192 square feet of load. Using the high number of 6,000 lbs, this takes your PSF rating down to about 31 or so, so at that point, the headers are your limiting factor.

On the other hand, have you considered just spanning the 16' dimension with 2x10s and placing them on 12" centers? You still have to support it wil a beam in the other direction, but then you could shorten the 12' span that way with knee braces, and when you get it down to an 8' span, a 8x10 supports almost 8,500 pounds.

I don't know - a lot to think about and there's always more than one way to skin a cat. Probably the best thing to do is to be realistic with what you think you want to put into the loft, or could possibly put in the loft in the future, and work backwards from there.

Good luck and take care.

KennyG · Apr 8, 2014

X bracing works but I think a solid block is easier and better.

slvr98svt · Apr 8, 2014

Ok gotcha on the solid blocking is better.

Tim, so are you saying run 2x10's in the 16' direction, so parallel with the 8x10 headers? I understand I would have to support it with a beam running between 8x8 posts, but that would be stronger than using the 8x10 as a header and setting the 2x10's on that? Honestly I just want to be able to put hay up there and have it be safe. I bale with a NH 315, and make about a 50# bale. I want the barn to look fairly authentic as a post and beam and that's why i planned on running the 2x10's the 12' direction, but if going the other way is stronger then i will do it that way.

Oh, and the corner braces are actually 9-1/2' apart on the header so they take up quite a distance. Not sure how much that will help. Would up sizing my header to 8x12 and subsequently going up to 2x12 be better?

Is there a decent visual aid in figuring these out. The tables I find online confuse the heck out of me!

Thanks,
-Matt

rtimgray · Apr 9, 2014

I was merely making a point that just because a given floor joist can handle a certain load doesn't mean that what it will attach to will handle the same load. In our example above, the joists can take a load of 90 PSF, but if they are attached to 8x10 headers, the header is only strong enough to hold a total load on the floor of 30 PSF, so in that case, either the joists are "oversized" or the header is "undersized". Another big consideration is the method of attachment used for the joist to header connection and header to post connection. Even if you increase the size of the headers, if they are not properly attached to a post, then that could be a failure point.

I'm sure the corner braces help to reduce the span of the header. In that case, with the braces about 10' apart (I don't have a chart that shows 9 1/2'), an 8x10 should support about 6,800 pounds. Since some of these will then have to hold an area of about 10' wide x 12' long (120 sq ft), that gets us up to about 57 PSF available for floor loading, which would probaby allow for stacking bales 5 or 6 high, which is probably high enough.

One other thing to consider - I imagine that all of the members strengths are probably greater than we are stating, because span tables and such tend to aim at the low end of the spectrum and err on the safe side. Probably my biggest fear with this project would be the plan on using rough cut lumber that is typically much more difficult to deal with than store-bought. I would also have some concern that the larger beams, like the 8x10s, being completely dried so that they do not continued to dry/twist/warp/bend after they are installed and potentially pull away from fasteners. Again, folks have been building barns with rough cut lumber, and I would bet most of it is green/not dried, so it would warp/twist/bend much worse than what is in question here.

I think you're probably fine with the plan you have, so long as the pieces all get connected good. If you build it as shown, I wouldn't be afraid to climb into the loft and help stack the hay.

Good luck and take care.

flusher · Apr 9, 2014

You can handle longer spans using DIY glulam/nail lams by doubling up 2x10s or 2x12s. Use exterior grade wood glue and a good nail gun. I used doubled 2x12s to span 14 ft sections for my equipment shed.