back to the 9 mile crossing topic...

[martini]

A freind and I were talking bridges the other day and came up with what I think may be a good solution. It's simple, should be quite effective, and would blend in to the surroundings quite naturally.

The idea is to use telephone poles again. Not in the manner previously discussed though. The idea is to use 4 of them for the main channel support. Use a dove tail or other joining feature to allow them to span the crossing. Bolt them together at the 'top'. Our idea is to have it kind of at a lower angle so the 'points' aren't so high, maybe 2.5/3 ft above the decking. This shallow angle could allow for a signigicant footing, making the bridge potentially resistant to flooding(keep in mind I'm NOT an enginneer here folks!).

For the decking, another set of utility poles would be used. They would fit into notches cut into the spanners, and also bolted in. The decking meterial of choice would then be either slipped into notches cut into the deck supports, or fastened to the top of them. Width? 36 to 48" or so. Wide enough for humans on bikes or simply walking, but not wide enough for snowmachines or ATV's.

http://www.fox302.com/userdata/martini/files/Photoes/bridgeidea.jpg

Do you think this may work? Or is not up to enginerring snuf according to the DNR folks?

[gopherhockey]

This is quite interesting. Thanks for sharing! Everyone knows I'm all for doing something other than the raft. Hopefully one of the river bottoms guys will reply on this.. Don?

[Don Youngdahl]

I'm a mechanical engineer with limited structural training, but I've done lots of small trail bridges & discussed structural issues with more qualified civil engineers on occasion.

I think they would question the lateral stability of this proposed design, as well as the stresses on the wood at the fastening points. If the stess on the wood is greater than it's yield strength, the bolts will tear out of the joints. What would keep the triangular members from tipping sideways?

The basic idea of using a triangular member as the support truss on either side is sound, but the 80 foot span is just too great for the simple wooden structures we have envisioned.

I love to build trail stuff, as you can see, but as Dirty Harry said after he blew away another bad guy, "A man's got to know his limitations!"

Don Youngdahl

[mAnTraMan]

Hi there:

I'm new to this so please bear with me if I blunder.
When I was in Boy Scouts back in Chicago we used to go to a state park where the hiking trail crossed a river a couple of times. Rather than build bridges they had stretched 2 cables across the river as a sort of "rope bridge". The cables were attached to a tree on either side of the river, one cable low and the other about 6 feet higher. You then walked on the low cable and held on to the high cable. Some of the short kids could not reach the top cable and so I would have to go back and forth holding on to a little kid while sliding my hand accross the top cable. This worked really well. My thought is that this is a very low tech solution to a bridge. Floods could wash over it without washing it away. I know it sounds a little dangerous but no more so than the old tree that used to span the creek. And isn't a little danger why we ride bikes in the woods?

[gopherhockey]

How would one get the bike over to the other side in this scenario?

[mAnTraMan]

I would carry the bike on my shoulder with one arm through the frame.

[gopherhockey]

Hmmm.. I guess I could see doing that. Would probably see an increase in people getting wet doing that, but heck I'd try anything over the raft.

Frustrating that all ideas seem to be shot down for one reason or another. My guess is that nothing really could be done without involvement from the land managers and getting their engineer approval.

If mother nature would just drop one of those big trees we'd have the problem solved.. ;)

[Don Youngdahl]

Last time I was down there, there was already a "rope bridge" like the one described, about 100 yards north of the raft. With a long span like this, the rope will have a fair amount of slack, which makes it harder to use than a tight rope.

Perhaps the people with good acrobatic skills will use the rope, and reduce traffic on the raft on busy days.

Don Youngdahl

[mAnTraMan]

Back at the scout camp they used wire cable about 1 inch thick. It was strung tight and the large cable did not stretch. I have not been down to the river lately to see the blue ropes, sounds like it could be fun.

[lou1s]

Saw this on mtbr.com, immediately thought of the River Bottoms, should the raft need replacing. Thoughts?

http://forums13.consumerreview.com/crforum?14@166.mztuavfMPnv.0@.efcfe37/0

eric

[gopherhockey]

Too cool - I'd even ride river bottoms again if the raft were replaced with this. Looks like fun!

[SickBoy]

This beings up a question in my mind - do we have liability concerns when it comes to what is implemented for a creek crossing? That thing looks cool and all but what if someone falls off it....

The creek/river is so low right now we could almost forego this whole raft thing though, just dump a bunch of logs in the bottom of the creek and walk/ride across... but it won't always be that way.

[Tetreves]

great idea, but the mom and pop bird watchers using the trail would be scared to death! (and hence complain about mt. bikers...)

Just a thought.

[Don Youngdahl]

I inquired about the total span of the conveyance, and it is about 36 feet. By comparison, our span would need to be about 90 feet or more.

Don Youngdahl