Making a foot bridge, need some help

I am building a foot bridge over a creek. I don't want to try and sink footers/posts in the creek itself, I am wondering how long a 2x12 can span. I am able to find 26 foot treated 2x12's locally. If I sandwiched two of them together on each side of a say a 3 foot wide foot bridge would that work? The ends of the bridge will be treated 6x6 posts (so 4 total). The span between posts will almost be the full 26 feet. My question is:
1. is this safe? 2. is the perfect? 3. is this overkill?
Thanks David
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On 6/2/18 6:44 PM, david wrote:

Would a flat truss be a practical alternative?
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On 6/2/2018 7:44 PM, david wrote:

I don't know for sure, but you can play with some numbers here and get a rough idea http://www.awc.org/codes-standards/calculators-software/spancalc
According to this, you need some support, but this may be to drive across. https://www.askthebuilder.com/bridges-joist-sizing/ If you are going to build a small bridge that spans perhaps 8 feet or less, I would use 2x8's that are placed 16 inches on center. A span of 12 feet would require 2x10's and spans between 14 and 18 feet would require 2x12's. Anything over 18 feet would require 4x4 or 6x6 posts mid span to cut the actual span in half.
If you are thinking of building any bridge with a span greater than 20 feet, you better get a structural engineer involved, plain and simple.
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On Saturday, June 2, 2018 at 8:53:02 PM UTC-4, Ed Pawlowski wrote:

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Using that span calculator if you build it 3 ft wide, use 12" spacing, which would be four 2x12, best wood, accept maximum deflection, minimum loading, it's just barely at the limit at 26 feet. I think others are right here, there are other better solutions, but they are likely going to cost more and be more involved. Another factor to consider is how sound the earth is on either side for the support.
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On Sun, 3 Jun 2018 07:39:08 -0700 (PDT), trader_4

He could always go with a swinging bridge.
http://gfretwell.com/ftp/Ed%20Labrador%20Memorial%20Bridge%20B%20test.jpg
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On Sat, 02 Jun 2018 23:44:02 GMT, david

The easy answer is engineered trusses. You can do that with 2x4s in most cases. The trick is finding someone who can assemble them with stainless truss plates.
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On 6/2/2018 7:44 PM, david wrote:

>
Are you the new contractor for the Florida International University pedestrian bridge repair project?
Anyway, maybe try this design:
https://en.wikipedia.org/wiki/Footbridge#/media/File:Wooden_footbridge_in_Vang_Vieng_and_blue_sky.jpg
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