Well actually it will be built with cable, not rope. It will have wood treads and it will only be a footbridge.
I’m gonna build this bridge across a small cove and it will be about 50 feet long.
You know the kind of bridge I mean, like the ones in all the Indiana Jones movies that all the bad guys fall from into the crocodilies.
Anyway I’m looking for input and construction ideas from anyone who has built one.
Thank You!!
Brookfield Woodworking
Cushing, Maine
Edited 7/16/2002 9:52:53 PM ET by Eli Ellis
Replies
Eli.............I've only built short span rope bridges with the local scouts and have spent a little time learning a little about vector resolution of applied forces/loads.
What I do know is that a 200 lb. man on the center of a tight rope bridge exerts vector forces at both ends of the rope far larger than 200 lb, hence the need for 3 to 4 deadmen at the ends of the scouts rope bridge.
A 50 foot suspension bridge has significantly larger loads and resulting vector forces.
Vector resolution of your design can tell you the applied forces at the ends of your cables therefore allowing you to select the right sized cable, the amount of dead weight mass needed to keep the bridge from collapsing to the center of the span, and the correct sizes of footings and uprights.
The specific design of the suspension dramatically influences the calculated forces. This is a complicated process and requires far more than I know how to do. .............so.
Pick a design first........then pick a bridge engineer. After all it will be precious cargo that transverses your bridge and you will bear the burden of a collapse and fall into the cove.
Good luck.................................Iron Helix
sounds like you'll need concrete foundations for steel cables. but i'm no engineer.
I plan to drill in the grainte ledges either side of the cove and set in eye bolts.
That will be a new task for me as well, advice anyone.Brookfield Woodworking
Cushing, Maine
-serious drilling!
Assuming you find out enough about everything else, be sure to use forged overhead load rated eyebolts (pricey) and not a bent and welded cheaper part.
Look at the Tennesee state parks web sites, they must have had a bridge engineer at one time as quite a few of their state parks have 50 to 100 foot cable bridges. They all look to have quite extensive side sway cable stabilization also.
Eli you lucky dog! I have never built a rope suspension bridge and would love to do so. I have drilled anchors into solid rock though, for a variety of purposes. It's really pretty darn easy with a rotohammer and if you don't have one big enough the rental yard does. I'll bet the HILTI guy in your area has some epoxy for you too. Do keep us all informed about your progress.