# Chain/rope bridge



## dubthang (Apr 2, 2009)

Has anybody built any bridges that where on chains/rope? I was wondering how the ridabilty of such a bridge would be. I had an idea for a bridge that could be made of planks bolted to chain runners that could be anchored on either side. This would allow the bridge to be rolled up for easy transport on the trail. One would just need to have some good anchors on either end to prevent sag and collapse of the bridge.


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## formica (Jul 4, 2004)

The skills park in Rossland BC has one, lemme see if I can find a pic -- I have some but I will have to resize them. IF you pm me your email I will send them to you.


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## swampboy62 (Feb 10, 2009)

I think they used to have one at Vultures Knob in Ohio. I think the video on the Spokejunkies site has some footage.

Steve Z


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## dubthang (Apr 2, 2009)

That Spokejunkies vid showed a good suspended bridge at the end. I don't plan on making anything that big, but it shows that it will take a little bit of skill to ride. Thanks.


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## PepperJester (Jan 2, 2003)

I built one once on a whim. Did not think over the design as much as I should have but it worked out in the end. It's a hoot to ride. Ours is about 15ft across, might be a tad slack now, going to go in and pull some more cable on in next time I'm on the trail.


will drag up a pic for ya,


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## ortedd (Jan 14, 2008)

*some examples around seattle*

There is one at the Colonnade bike park in Seattle with chain stringers. Some one on the Washington forum could tell you the specifics of how it is constructed and anchored. I think they used trex decking (something similar) carriage bolted to the chain. Not sure how they anchored it at the ends.

https://evergreenmtb.org/img/upload/img00482.jpg

There is also an old suspension bridge at PCVA where they wrapped fire hose around two large logs (anchor points at ends) and nailed the heck out of it. I believe on that one the decking is just nailed in from the backside. Some real heavy ratchet straps would probably do the job as stringers for that style of bridge.

Cut one one of these in half and you could have about an 8 ft span
https://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=36612


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## dubthang (Apr 2, 2009)

Thanks for the pics. The hardest part I'm having right now is coming up with a way to anchor the bridge in place. There is a whole lot of mud and dirt here in Maine, and not many giant rocks or deadfall to anchor into where that type of bridge would be needed. I may have to haul some concrete mix into the trail to create a solid base for some anchors.


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## ortedd (Jan 14, 2008)

Are you trying to cross anything (gully or creek) or looking to build a feature on relatively flat ground?


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## dubthang (Apr 2, 2009)

It'd be for a water crossing. I was trying to come up with an easier way to lug a bridge into the woods (and add some fun while riding it.) The banks are generally sloped hard pack. A flat wooden bridge could just be laid across, but a chain bridge would need a hefty anchor system so that it wouldn't pull out of the ground.


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## ortedd (Jan 14, 2008)

*a concept*









You could try to drive an angled anchor (such as galvanized fence post) out past the crossing. This combined with the vertical supports shown in the attached drawing would triangulate the suspension portion of the bridge. The vertical on the suspension bridge is carried by the vertical supports while the tension in the flexible members would be reacted through the anchors that you drove into the ground.

You would not want the bridge to be suspended on the way up to the vertical supports because it would tend to exert a side load on your vertical supports.

If obtaining on site materials for the on/off ramps would be difficult, you might even get away with putting just the anchors further up the bank and draping the flexible bridge member on the ground.

Depending on your soil those anchors might loosen up over time.


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## dubthang (Apr 2, 2009)

Thanks for the pic. I had something like that in mind, but I think I would need to either connect the anchors to each other and/or to the vertical supports. The reason is that come spring time, I'd still want the bridge to be there after the snow melt/river rise. It'll be quite a project. 

The other idea that I had was to build a full length bridge outside frame, and suspend the inside. The frame would keep the chains in place, and allow me to not need ground anchors.


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## YoPawn (Mar 26, 2008)

That one at Colonnade wasn't anchored into the ground well enough and kept breaking. They had to anchor it deep into some large rocks.

Overall, it's a lot of work and maintenance to results ratio. The Colonnade one was constantly breaking, and might still be. 

They are also difficult to make it easy to roll over, since it has to be very tight.


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## fishbum (Aug 8, 2007)

check these out: http://pacifi.ca/photos.html
Built all out of 2x4's... Get a bunch of people and hump the lumber out to the location and build it in place. My guess is it would be a lot less work and cheaper?
Unless you are shooting for the awesomeness that a suspended bridge would be!


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## Skookum (Jan 17, 2005)

YoPawn said:


> That one at Colonnade wasn't anchored into the ground well enough and kept breaking. They had to anchor it deep into some large rocks.
> 
> Overall, it's a lot of work and maintenance to results ratio. The Colonnade one was constantly breaking, and might still be.


The stringers are permanently fixed into huge limestones, and they did work free, but the rocks have been re-set, and reinforced. The stringers are not very tight, sways low so to speak, so as the picture shows a rider dives into the bridge and through, which creates much more force than if it were a tight spanning bridge.

The other maintenance issue is due to using the Trex like material. It's choicedeck a Weyerhauser brand. The material spec requires having a certain type of screw, other types work it's way out, so the belts which keep each Choicedeck slat from moving independantly as well as reinforcing each other keep letting loose. It's likely that bridge's slats will be replaced with a different type of decking someday.


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## ebxtreme (Jan 6, 2004)

Here's one on Galbraith Mt. Trail is Scorpion......sorry, the snow pic is all I've got.

This is anchored into two very large logs, has cabling and you end up on the logride on the right side of the pic. It's a pretty fun move, but I don't know if I'd want to ride one of these across a long span or very high up.

Cheers,
EB


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## dubthang (Apr 2, 2009)

Thanks for the links and pics people. I am working on a couple of different designs right now. When I get something more solid, I'll post them up for feedback.


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