# Bridges over >16 foot span



## TunicaTrails (Jun 29, 2009)

Hi there, on my home trail I have a conundrum, a span of approximately 25-30 feet where a wooden bridge my neighbor built was taken out by a fallen tree. The drop into a gully is also about 25-30 feet. 

Normally for bridges elsewhere, I'd hammer something together with 2x6x16s and be done with it. There are no good reroutes or shorter spans, unfortunately. I'm looking for ideas for a cost-effective new bridge. What's the best design?

Thanks


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## Trail Ninja (Sep 25, 2008)

Pictures? Are there any restrictions? Can you get equipment in to the site? To span 30 feet to code you'd need an engineered truss, massive beams, pillars or a suspension system.

Did your neighbor's bridge work? How about rebuilding that?

With no restrictions I'd build across the stream down in the gully and take the chances on flood washout. The cheapest and easiest way to go. Certainly not the best way.


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## smilinsteve (Jul 21, 2009)

Are the abutments still in place from the old bridge?
Was the old bridge a single span, or was there a pier in the center?
Is this only for foot and bike traffic?

A 30 foot span is no simple bridge. If you could put a pier in the center that would simplify it. You need some pretty hefty I beam or telephone poles, I would say.


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## TunicaTrails (Jun 29, 2009)

Thanks for your interest, I'll post photos tonight. Restoring the existing bridge, or at least using the materials (that are now washed out into the gully) is a good idea. The span is a little wider now after erosion due to Hurricane Gustav. 

I'm looking to do this with limited manpower also as it's just a trail for family, neighbors, and friends. The landowner is an architect who built the original bridge, and I'm trying to do him a favor by fixing it for him since I'm grateful that this trail can be partly on his land.


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## Trail Ninja (Sep 25, 2008)

So you may be able to sneak around building regs if it's a private trail. You can get a lot more creative with your bridge design if you don't have govt. inspectors hanging around.

I have to go find the wooden stick arched bridge I saw a couple of years ago.


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## Trail Ninja (Sep 25, 2008)

that was easy.

http://mathemati.ca/Log.html

I've made miniature versions of these. they work.

I built a 10' span 12" wide with a load of over 250lbs. made with 1" to 1.5" poles.


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## Loren_ (Dec 3, 2006)

Your tax dollars at work:

http://www.fs.fed.us/eng/bridges/drawings.htm


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## bankerboy (Oct 17, 2006)

Trail Ninja said:


> that was easy.
> 
> http://mathemati.ca/Log.html
> 
> ...


Very cool lookng bridge. It would be very primative looking in the wild. Better than some of the more traditional means. I don't know if 1.5" sticks would satisfy me but I don't that the land or the means to try it out. Let me know how/if it works.


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## Trail Ninja (Sep 25, 2008)

bankerboy said:


> Very cool lookng bridge. It would be very primative looking in the wild. Better than some of the more traditional means. I don't know if 1.5" sticks would satisfy me but I don't that the land or the means to try it out. Let me know how/if it works.


Definitely works. I took apart the one I built because it was just a test.

I build some pretty primitive stuff. This is a ladder made from some milled wood I got but the structure is compression fit round tenon joints and the decking is held on with compression fit hand carved dowel. It's as solid as anything bolted together and when it rots, there's nothing left lying in the forest like bolts or nails.

View attachment 574972


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## Fattirewilly (Dec 10, 2001)

TunicaTrails said:


> Hi there, on my home trail I have a conundrum, a span of approximately 25-30 feet where a wooden bridge my neighbor built was taken out by a fallen tree. The drop into a gully is also about 25-30 feet.
> 
> Normally for bridges elsewhere, I'd hammer something together with 2x6x16s and be done with it. There are no good reroutes or shorter spans, unfortunately. I'm looking for ideas for a cost-effective new bridge. What's the best design?
> 
> Thanks


This company came recommended to me

http://www.ettechtonics.com/pedestrian_and_trail_bridges/index.php

I have not used the product


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## Trail Ninja (Sep 25, 2008)

Any idea of the cost willy?


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## Fattirewilly (Dec 10, 2001)

Trail Ninja said:


> Any idea of the cost willy?


For some reason $40/SF sticks in my head. A decent deck is what, about $25?? They come pre-engineered, so the designing aspect is taken care of. They come in pieces that can be carried in by 2 or 3 people per chunk. Boyscouts can put them together, so I've heard.


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## smilinsteve (Jul 21, 2009)

Fattirewilly said:


> For some reason $40/SF sticks in my head. A decent deck is what, about $25?? They come pre-engineered, so the designing aspect is taken care of. They come in pieces that can be carried in by 2 or 3 people per chunk. Boyscouts can put them together, so I've heard.


There are lots of prefab bridge companys. US Bridge, Exel, Contec, Wheeler, Big R, etc. 
They are not cheap, and it sounds like we are looking for a more affordable answer here. 
30x6 = 180 sqft x$40 = $7200.

I don't know about fiberglass bridges, and maybe they are around $40, but for the steel prefabs, the cost may be closer to $80/sqft.


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## smilinsteve (Jul 21, 2009)

Loren_ said:


> Your tax dollars at work:
> 
> http://www.fs.fed.us/eng/bridges/drawings.htm


It looks like the "multiple log stringer" bridge is the ticket. Nice plans. You need 3 logs, about 16" in diameter by 30'. Maybe some old telephone poles?


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