I have a creek I need to cross with a footbridge. While the creek is only about 3' wide, the main span of the bridge will have to be somewhere between 14-17' feet long, due to low, wet, and loose ground around it. I also have to deal with wetlands regulations, so I don't want this bridge to be something large that is part of a major project. It'll be easier to get approval (due to wetlands regulations) if I stick with just wood rather than pouring concrete footings or using other materials or making something like a suspension bridge. I'm hoping to keep this bridge to a 3' wide walkway with simple railings.
I've found this site on building arched footbridges (he calls them "rainbow bridges"). If I went that way, it would be much more complex than just a flat bridge and I'd have the issue of having to make concrete footings specific to the bridge plan to handle the forces at the end of the arches.
I've seen at least one video of someone making a flat (non-arch) bridge with a 12' span using paired 2x6 boards for each beam. I have found tutorials on span tables, but I'm not clear if information designed for a larger surface area such as a floor or roof applies to a walkway or bridge that's only 3' wide, where the load is spread out over only 2 or 3 beams. Also, since the load would be people walking on it, I'm not sure how that breaks down to the amount of weight per square foot.
The idea of using paired or laminated boards as beams sounds appealing, since it's much easier than building an arch.
Will span tables work just as well for what I'm doing as for floors or other surfaces? If not, where can I find information that will give me an idea of what I'd need to use (such as paired or laminated boards for supports) to give me solid support for a span as long as I need?