# Bridge building questions



## creekchubb (Mar 16, 2006)

Ok, there is a spring that flows across our trail, and we have been using pcv pipes covered with a couple of pavers. I want to build a bridge, more of a long term solution. Any thing I need to consider. it will be @ 6 - 8 feet long, and only a foot above the ground. How wide should I make it? How do I anchor it in the ground. any ideas on design?


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## woodway (Dec 27, 2005)

Things to consider and questions:

1. Is the landowner aware and OK with you building the bridge?

2. Width depends upon the type of use and the skills of the riders who will be using the bridge. The less skilled the rider, the wider you should go. 2-3' wide is pretty good for most riders.

3. How you anchor to the ground depends on many factors, incuding the wishes of the landowner, the type of material you will be building with, local conditions and how long you want the bridge to last. Give us an idea of the above and we can provide some suggestions.

4. What type of materials are you going to use for the build - dimensional lumber or materials salvaged from the site?

5. What are you thinking for decking?


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## dcrowe (Oct 9, 2009)

For most purposes 24" wide is good. It's really hard to fall off unless you are really trying hard and works well with common lumber lengths. 

The parts of a bridge are sills (sits on the ground) Stringers (the parallel beams that provide structure) and decking. For entrance and exit we will typically use rock and gravel or dirt to build ramps. 

Place your sills on rock not dirt. ie dig dirt out and fill hole with rock so the wood only touches rock not soil. Don't undersize your stringers... I like 4x6 as a minimum 
(or round equivalent) for a 8-10' span. For decking I prefer rough cut 2x with 4" ardox nails 2 to a side.

If you are building with log use dry wood - standing dead on the ground, green is okay for stringers and decking.

Or you could just leave your pipes in place and allow drainage under the trail by elevating the tread. But for that you will need a lot of rock and and a good dirt source.

Hope this helps, Derek


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## Dickweed (Jul 14, 2009)

I make all my bridges 32" wide - that allows me to get 3 treads from each 8' 2x4 or 2x6 that I used with no waste. I tend to create some pretty long (and elevated) bridges with curves and banking built in and 24" would be too narrow.


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## fishbum (Aug 8, 2007)

We build ours 24" wide, most are low to the ground. Hikers, trail runners and mtn bikers use them


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## dcrowe (Oct 9, 2009)

Good looking bridge. 

I really need some pics to illustrate but they are not here with me on this job... With curved bridges I like to let my decking run wild at 29-30" and then trim with powersaw to minimum 24". I just eyeball it until the line is fair and sweet. I use an Alaskan Mill to produce decking which is super efficient especially when run by an enthusiastic 20 year old or two. I provide sharp chain and encouragement. 

Will try to remember to get some pics.


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## zachi (Jul 25, 2006)

Build it to last with inexpensive and native material....Stone!

www.foresttrailsalliance.org

Check it out and let me know if you have questions. Gallery has photos that shows steps in constructing a stone arched bridge. One the size you are talking about is 10 hours labor, $25 cost.

Zachi


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