How does the larger wood work for warping and cuping? Will it hold surface water after a rain? If so, would it be slipery??
I have a 2' wide "walkway" (actually scaffolding I have had up for 15 years in front of my house--they why of this has a lot to do with building permits and an obnoxious neighbor), with PT 2x12 as a deck. It is screwed down with deck screws 3 places at each end. It is exposed to the rain. No warping or cupping in 15 years. I don't remember, but I think I drilled holes for the deck screws so the ones at the edges of the 2x12's wouldn't split the wood. You would only need to do this on the ends whatever you use for your deck.
I think if you screw it down to each beam you will prevent warping & cupping. My neighbor (not the obnoxious one) has a 30' bridge with 2x12 decking and it is still perfect after ~18 years.
If you have the beams on 12" centers, I doubt it will warp, since I have examples with wider beam spacing which are still OK.
I have a foot bridge with 2x6 redwood (non-PT) decking leading from my driveway to front door which is very slippery after a rain. The PT wood is "stabbed" every couple of square inches to promote penetration of the PT solution. This gives a rougher surface which is significantly less slippery than smooth wood.
...wouldn't I-Beams be more permanent and last longer? I've seen I-Beams that are over a hundred years old, but I have no idea how long the Preasure Treated wood will last as a bridge.
There are non-PT wooden bridges well over 100 years old in the northeast, as well as wooden buildings. I think most of them are reaching end-of-life. As far as I know, PT increases life so who knows how long that would last?
About 20 years ago I worked with a guy who lived in England. He had family money and used to brag that there was a beam in his house with the construction date -- 1620 -- carved into it. One day we got fed up with his bragging and asked him if there was some reason why he couldn't afford a new house. This torqued him off more than I thought it would, but demonstrated that wood will last several centuries in a protected environment.
I agree that I-beams would last longer than PT wood, but I suspect the wood is going to outlast either one of us. Does it really matter? If the deck is PT wood, this will be the first thing to wear out, although the stringers (ledger boards?) you are talking about putting on top of the I-beams will trap water between themselves and the I-beams. If I used that design, I would think about marine grade PT for those...
As a practical matter, you only need the bridge to last longer than the rest of your RV park. When your park is successful, you can replace the wood with platinum-plated titanium in 50 years. /forums/images/graemlins/laugh.gif
You seem to be self-financing a grass-roots startup. I have had a few small businesses over the years. The most important objective is to get the business open before you run out of money. "Better" is the enemy of "good enough".
Thank you for taking the time to write down all that information!!!
You flatter me. I am an engineer -- I like thinking about this kind of stuff. Your project is fascinating, your posts are good, and you have a wealth of practical experience.
Keep up the posts!
