Rope or Steel Cable Pedestrian Suspension Bridge

[barry sacher]

 

i’ve got a client in orinda, ca, with a wide natural drainage swale on an acre property.

we want to span it.  the swale is only about 8′ deep where we want to cross it, but is about 35′ wide.  we can reduce the span using cantilevered deck platforms at either end, but the bridge section will have to be 25′ wide or more. we can’t use post supports and build a deck bridge because of the drainage that runs through the swale.  i’d like to use PTDF slats, 4′ wide for the bridge decking, and it will need simple rails.  It should be able to support 1000 lbs, or close to it.

i’ve been researching engineers and some children’s playground construction companies but haven’t found anyone yet who’s right for the project.

anyone have any experience with this, even on a smaller level?

[Thomas J. Johnson]

Hire an engineer…

Rope? That’s some serious rope…  

1,000 lbs of people or 800 lbs of decking and one 200 lb person?

You’re only able to gain 5′-00″ on each side with cantilevered platforms? I bet you could get 10′-00″ on each side and only need a 15′-00″ bridge but that might look goofy…

Having a drainage doesn’t prevent you from using a column support in the middle but there might be a more elegant solution…

Do you only want to move people across the bridge or small vehicles / horses, etc. too?

How much money do you have to spend?

How stable are the banks?

My vote: Stone arch from materials found on site. Strong, cheap and timeless…

[Chupacabra]

One project I worked on recently had a 300′ steel cable pedestrian suspension bridge as an alternative (wasn’t selected – way out of line with the site’s sense of place, plus costs, plus impacts to archeological sites).  The cable support posts were going to be around 80′ tall and the cable anchors would have had to have been set back 100′ or so beyond the bases and 40′ deep (if I recall correctly).  The prime on the contract was an architecture firm and they subbed the bridge design out to an engineering firm (it was part of a 1000′ boardwalk system).  This bridge and boardwalk system was being designed to support up to 10,000 pounds, so quite a bit more substantial than you are looking at.

If you can put some posts in the swale (why can’t you?) you can find companies that make prefab bridge spans up to 15′ long which would be much, much cheaper and simpler.

This probably doesn’t help any, but there you go.

[Jordan Lockman]

Have you looked into pre-engineered bridges. I attached a link for a local MN company that sells about the size you are looking for.

http://www.wheeler-con.com/recreation-bridges/

I like this one.

http://www.wheeler-con.com/pdf/RTbrTrusPrat12-30-09.pdf

[Jordan Lockman]

Stone Arch Bridge sounds awesome but really expensive.

[mark foster]

I recently researched building a bridge across a stream and came across (many) companies using railroad car beds.  These would definitely be long and strong enough.  Here’s one:  http://www.paragonbridgeworks.com. 

[Author]

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