# Light Weight Stringer Ideas?



## jonas_24112 (May 16, 2016)

My local trails has a great loop through a pretty creek bottom. As such, the bridges that are there are starting to rot. Most are 10' or under. No motor vehicles are allowed (except a trail excavator/ditch witch in the past), so I need to pack in the materials to repair the bridges. Packing in boards is no problem, but bridge support/stringers may be a bit more difficult due their weight. I would like to avoid cutting down any trees for support as most of the standing trees are are pine and would rot quickly. 

Besides the usual treated 2x6, 4x4, etc.; any ideas for cheap lightweight stringers?


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## zrm (Oct 11, 2006)

Nothing that isn't really expensive. At 10' you could use something like aluminum square tubing but you'd need a source and like I said, that sort of thing would be expensive.

FWIW, I used treated 4X4 with 3 stringers on short span bridges with 2x10 decking on a couple busy non motorized trails and they're going on 20 years old and holding up great.


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## aero901 (Apr 11, 2012)

Believe it or not, wood is still one of the lightest and most cost effective materials for trail bridges. At only 10 ft in length the stringers required should be easy enough to haul in with a few people and maybe a specialized cart. We just built a 12' bridge with 2x8 stringers and it was a piece of cake to haul it in (in pieces) with a crew of 5. If the bridges were longer (+20') there are other options, such as metal floor trusses, but 10' isn't long enough to justify the upgrade.


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## WHALENARD (Feb 21, 2010)

You could haul in individual PT 2x10 or 2x12. General rule of thumb is 1" per 1' of span so for a 10' span a 2x10 16" on center should be fine. If you want to beef it up or go 24" or greater on center lag the corresponding 2x10 or 2x12 together on site.

Let us know how it goed


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## old_MTBer (Feb 16, 2014)

Over the years we built over a dozen bridges of various lengths using this set of plans. I found this set of plans on the IMBA web site some years ago. I don't know if it is still there. These were designed by an engineer who is also an MTBer.
https://www.dropbox.com/s/q8cie82w3pshqxm/trailbridgedetails.pdf?dl=0

Here is a weight chart for standard sizes of pressure treated lumber from this web site.
Lumber - Weights


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