About ten years ago I built a woodshed on the side of the hill where I live. It has 9 posts, (10 inch diameter fir log sections), supporting three good sized (>12 inch) log beams parrallel to each other. The logs are 24 feet long. Since they are supported by posts in the middle, they effectively span about 12 feet.

Running across the log beams I have 4x8 full dimension douglas fir joists on 24inch centres. They span about 12 feet. The floor over them is 2x6 fir planks.

The total floor area is about 24 feet by 24 feet, and the 4x8 joists each span about 12 feet, since there's the log runnding down the middle.

I'm using one quarter of this area to store firewood. This year I have more than usual - about four cords of various types of wood. Some of the new stuff is pretty heavy - pitch filled fir and arbutus. I'm wondering how much this floor can support.

I'm guessing the wood averages 2 tons per cord, or a total of 8 tons. That would mean the floor is supporting an average of about 110 lbs per square foot in that quarter of the shed. (144 square feet X 110 lbs = 15,840 lbs).

Does anyone have any idea about how safe this is? I've only got three of the cords in there, and I'm wondering about the fourth, which is arbutus, the heaviest of the wood.

I believe the logs are safe, and the posts are well braced, but the 4x8 joists - don't forget, they're full dimension - they might be close to their limit. It still feels very solid to walk on. It really seems pretty solid, but I'd like to be reassured with the math. I couldn't find much on 4x8 on the web.

Any ideas appreciated.