Assistance needed: Beam sizing for pole barn loft

[Mark97133]

We are adding a loft to the back of our 40x60 pole barn. The loft will be 24x40 overall. We planned some for this when we built the pole barn and added some additional inside posts. I am looking at running the beams across the 40 ft lenght and then using joists across the 24 ft lenght.
The 40 ft lenght will be broken into 3 beams (roughly 12ft, 16 ft, and 12 ft)
The 24 ft section will also have a beam down the middle, so the joists are really only 12 ft, not 24 ft.

The post arrangement along each groups of beams are
6x8 --- 6x6 --- 6x6 --- 6x8

I am trying to determine the best way to size the beams as well as the best method to mount them.

I plan to use 2x8 joists with hangers, so I would rather stay near an 8" beam depth and go wider if possible.

Thanks

 

[ace10]

Is this for a storage loft, or workspace, or what?

 

[flusher]

We are adding a loft to the back of our 40x60 pole barn. The loft will be 24x40 overall. We planned some for this when we built the pole barn and added some additional inside posts. I am looking at running the beams across the 40 ft lenght and then using joists across the 24 ft lenght.
The 40 ft lenght will be broken into 3 beams (roughly 12ft, 16 ft, and 12 ft)
The 24 ft section will also have a beam down the middle, so the joists are really only 12 ft, not 24 ft.

The post arrangement along each groups of beams are
6x8 --- 6x6 --- 6x6 --- 6x8

I am trying to determine the best way to size the beams as well as the best method to mount them.

I plan to use 2x8 joists with hangers, so I would rather stay near an 8" beam depth and go wider if possible.

Thanks

I used doubled construction-grade 2x12s (glued and nailed) to span 14-ft between posts on the equipment shed I built a few years ago.



Also, used a lot of Simpson hardware to tie the components together.

Good luck

 

[Mark97133]

Sorry, I fogot to attach the rough layout diagram.
We are not set on a single use role for the loft, it will have some function as a work area and a function as storage. We would rather over build it some and not have any worries on future projects.

 

[KennyG]

This is a situation where you should follow the guidelines. There are span tables available for almost all situations. Try:

Span Tables :: Southern Yellow Pine

If you go to Table 5 at the link, it will show you that No. 2 pine 2x8 floor joists will support a 40 psf live load plus a 20 psf dead load with spans up to 12 ft 4 in. when placed at 16 inch centers.

Your center beam will need to be very strong, since they have to pick up half of the load on all the joists attached to them, but if you are using minimum 6x6 posts, you will probably be building this up at least triple thickness.

Since your spans are not long, regular 2 by lumber may be the best choice. On longer spans the engineered beams work better. I wouldn't double the 2 x 8's under any circumstance. Just spacing them closer would look better. The tables indicate you could get a total capacity of about 100 psf (which is a lot) at 12 inch spacing and that would let you store heavy items without much worry.

Looks like a neat idea. How high is your barn?

 

[Mark97133]

Kenny,
Thanks for the link. I should have mentioned that I was planning 12" spacing for the joists.
I am in Oregon and will be using Doug Fir.
I am still struggling with figuring out the beam size needed based on this.
I have not been able to find a chart of built up beams or one that will show me the loading for different beam sizes.
I do plan to have a uniform depth of the floor so if I end up with a 10" beam depth, then I plan to switch to 2x10 vs 2x8 and just expand the spacing.

The pole barn was built with an 18ft eve height so we could use trusses and still have a full height loft after allowing for the roll up door and floor depth

 

[KennyG]

Ok, I don't want to get all technical on you but is there a good reason not to have deeper transverse beams than your floor joists?

Think of it this way. If you have nominal 10 foot long floor joists on 12 inch centers, each is supporting the average floor loading on about 10 square feet. The center beams that support the floor joists will have to pick up the load for more like 100 square feet.

My approach would be to build up center beams from 2x10's or even 2x12's, laminated with plywood to bring them up to 6 inches thick to match the poles and then use 2x8 floor joists. I think that would give you close to 100 psf floor capacity at the lowest cost.

I don't have my engineering handbooks immediately available, but there are tables for beam strength. A composite with plywood and dimensional lumber is probably stronger and more rigid than a solid beam.

Here's a source for beam capacity if you want to wade through it.

http://www.awc.org/pdf/WSDD/TOC.pdf