I designed a 26' wooden bridge. Will it hold?

A freshwater stream bisects my yard. I'd like to build a bridge over it. But my budget is tight, so I'm thinking DIY. Here's a photo of the stream and some schematics of my proposed bridge: https://imgur.com/a/yKlCGaw

However, there's a challenge: The stream is wide, so the bridge must be quite long. I'm not sure how to install supporting posts underneath at the halway point, and anyway I fear they'd just erode (they'd need to be embedded into the sediment, which is submerged in the stream).

So this post seeks to get some feedback on my proposed design, to see whether you think it will be strong enough to support the necessary loads. Here are some details:

• The gap from bank to bank is about 22', so I figure my bridge should be 26' for about 2' of buffer on each side.

• The bridge will just be laid down on the ground, end to end, no concrete underneath the ends.

• The bridge is exclusively for people, most likely walking single file. I suspect <500 lbs of human at any given time.

• The combined weight of all lumber in the bridge should be about 1,500 lbs (confirmed).

• The entire bridge, including hardware, will probably be about 1,700-1,800 lbs (educated guess).

• This means that at its heaviest (so, with multiple people on it), about 2,500 lbs of downward force will be exerted on the structure (this includes a couple hundred extra pounds of buffer).

• All lumber will be pressure-treated southern yellow pine.

• The two sides are the most critical component as these will ultimately bear the entire load.

• I couldn't find a single 26' cut, so instead each side is composed of three "layers" of 2"x12" boards (see link above for the schematic of the sides).

  • To make each side as strong as possible, ...

1. **the layers will be glued together, then** 2. **carriage bolts will be inserted through all layers at 12" intervals, then** 3. **the side will be reinforced with a little bit of metal (e.g., [one of these (20') bolted to the side](https://www.metalsdepot.com/galvanized-steel-products/galvanized-flat-bar-?), or else [two of these on the inside bottom corner, meeting in the middle](https://www.agrisupply.com/1-1-2-x-72-slotted-angle-hdg/p/134152/)).** 

• Notice how each layer involves multiple cuts, but that the points where two cuts meet are staggered across layers. This ensures these weak points are distributed across the length, such that at any given point at least 2/3rds of the side is solid wood with no breaks.

• Hopefully all these efforts will result in each side functioning effectively like one single 4.5" x 11.25" x 26' (nominal) beam, strong enough to hold all the weight across the full span of the bridge.

  • The inner joists will be attached to the sides using corrosion-resistant face mount joist hangers.
  • The boards on top will be about 1" thick to minimize weight while still giving enough strength to hold a person, together with the joists (spaced 12" apart).

I should be able to secure all the materials I need for about $800, much better than the $3-5,000 contractors have quoted me for something more "professional". I just want to make sure this thing will be structurally sound before getting started.

Super interested to hear your thoughts. Thanks in advance for any advice you can provide!