For a horizontal platform 12 x 4 ft, made from #1 or #2 pressure treated pine dimensional lumber, with proper post and beam construction, galvanized connectors and joist hangars, what is the recommended spacing between 2x6x4 ft joists needed to support 8,000 pounds evenly distributed across the whole 12x4 sq ft surface ? You may assume the 2x6x4 joists are single or sistered as needed or recommended.

The spacing of the joists themselves should have no other restrictions since the platform will be loaded with two cords of split green oak firewood, so I don't see anything that would preclude any specific spacing except to hold the load over time without sagging. I just don't want to make a mistake and discover I should or could have used more or less spacing width between joists. Since this is firewood I'm assuming said calculations would assume a dead load, as opposed to a live load like a deck or a subfloor etc.

Though I doubt it makes a difference, the load will be carried by six 12 in diameter Sonotube poured concrete piers, with three 4x4 posts on the back, and front, supporting 4x6x12 ft long load bearing beams resting directly on top of the posts without any cuts or slots to achieve 100% vertical loading bypassing any shear stresses. The joists will then join the back beam to the front beam, supporting the floor that will hold the firewood.

We can also assume that instead of a wood floor for the shelf surface, I'd like to use some type of heavy gauge fence wire for the floor instead, resting on top of the joists, something like a cow panel or better, a horse panel with 6 gauge galvanized welded wire (.192 diam), something like this:

https://staytuff.com/product/2x4-horse-panel/

The reason for the wire panel floor instead of a wood floor is that my previous rig used pallet wood boards for the floor, but that was a mistake because it allowed too much wood/bark/dirt detritus to accumulate on the floor beneath the stacked wood pile, which became a problem after it was invaded by mice, rats, beetles, ants, and termites etc. I thought a heavy gauge wire floor would be much better, so all that crap just falls through to the ground.

I'm pretty clever but not clever enough for this. Given the expense and level of effort and work to build it, I really want to avoid screwing this one up.

After I build the raised platform, I'll build a lightweight back and side walls with lots of ventilation and a single slant roof, prob using a corrugated pvc or galvanized roof sheeting of some type to keep rain off the stack.

What do you guys think, particularly the calculations regarding the required spacing of single or sistered 2x6x4 joists needed to avoid any sagging ?

quote:

proper post and beam construction

A few years ago, I never thought I would question what this meant.
After following some construction, stair and framing groups I think that is an open assertion?

Steel would last a lot longer than wood.

Anyone that could answer that would be very much into the weeds of building codes, and my hat is off to them. The wood storage setups I see are almost always on a concrete pad of some sort.

You are very close to calculating your own answer.

What is the weight of the dead load?

What is your definition of sag? All beams will deflect and you should give the engineer the required maximum deflection.

To minimize deflection increase the beam section height from six to ??? inches. Sistering a six inch beam does not increase its resistance to bending as much as a greater section depth.

But sistering would in fact decrease the deflection I assume, since sistering joists is used to reduce deflection of floors under old houses, without increasing the depth of the joist itself.

The weight of the firewood load is 8,000 lbs, which I'm assuming would substitute for the "live" load, and the dead load would prob be say 5 to 10 lbs, divided by the area, is 165 lbs per sqft.

I suppose the max deflection allowed for the 48 inch joists could be, say, no more than 1/16 inch.

And the stiffness of southern pine, assuming it's dry, is whatever the specs are for dimensional lumber for that species as published by whoever is the sanctioning body for those building standards. I'm not sure what the units or definition would be, I don't remember that stuff from my statics class in college.

Just for the record I found a website that shows the formulas and subformulas to calculate it, including adjustments for wet vs dry timbers. It was hard to find. But there are plenty of other resources for finding the MOE for different types of wood for these larger manufactured timbers. There's enough information to put it in a custom spreadsheet for various plug-n-play. Pretty interesting.

I haven't calculated deflection in 20+ years, but I have built a few things out of wood & I suspect that 12, 16 and possibly 24" spacing will be just fine.
You're only spanning 4' or 6' between the posts, so you wont get that much point load in the center of any span.
12" c-c is going to cost you $20 in materials vs 16", you've already spent that in time thinking... I'd do 12" c-c for when the wood starts to rot, not for holding the load when it's new. Depending on how you are decking it, I might use some scrap for blocking between joists as well. Again, depending on decking you probably will notice more lateral deflection when you do have a moving load than you'll have vertical from a static load. Also, if you're decking isn't rated for much weight (fence wire), you'll need tighter spacing to keep it from sagging.

We have a bunch of WWII 'landing mats' that are like a 3/8" thick steel 2x2" grid for driving heavy vehicles on soft ground. I haven't looked at any in a long time, but I think they're about 42"x7' - we usually use 6 blocks to get them up off the ground when we want to keep whatever dry. I doubt I'd stick 8k lb on 1, but maybe 2 with ~10 blocks would work, I'd bet.

For the record, I just built a 5x12' deck on the back of my house with 12" centers & only 2 posts in front (ledger board on back). I used 2x8 for the rim joists, but 2x6 would have been plenty for the 5' sides and for the 12' if I'd had a post in the middle. 16" c-c would have been fine. Before decking, I jumped up & down on it and my 250lb fat ass didn't budge it. "that ain't going nowhere" was the final nail to hold it all together.

Hi snidera. Thanks for the help. My concern wasn't for the joists, those guys pass the calculations for evenly distributed load on 12 inch centers. My issue is with the beams, also continuous load without any point loading, with 6 ft spans. The deflection calc is within L/360, but one of the other two calcs fail, though practically it will prob be OK, since when the wood stack dries out it will weigh significantly less. I can solve it with two additional posts, but I don't wanna do it, it will look better with just the 3 posts on each side. I don't want to overbuild since it needs to look sharp enough without being overbuilt, and it's not supporting any life.