Lift Bridges

Lift bridges come in a variety of styles. Newer lift bridges are very cool!

2011

 
 

The Pathfinders Lift Bridge









        Most lift bridges have a counterweight, to balance the weight of the span, this way the motors that move the bridge up don’t have to lift the entire weight of the span (which can be a lot!). Also the counterweight only needs to be the weight of the span, not several times heavier, like in a bascule bridge, since the weight is not on the short end of a lever!

With some research you will learn that many lift bridges are used for railways, since the deck can be made with stronger materials, which are needed for the heavy trains. The truss system is well suited to this since it can be strong and relatively light. The disadvantage to the lift bridge design is the height limitation (see youtube videos).

While most lift bridges are made with a truss system, the Gustave Flaubert bridge in Rouen, France (crossing the Seine River) is a very cool non-truss design - makes you want to be an engineer! While not really a lift bridge, a table bridge also lifts the span of the bridge vertically, using hydraulics! Check out the table bridge in Oudenaarde. And while you’re at it check the Corinth submersible bridge. A very cool vertical lift bridge!


A great web site for more information is Wikipedia (bridges) and the Visual Dictionary. A fun interactive web site for kids is the PBS website Building Big (http://www.pbs.org/wgbh/buildingbig/bridge/index.html). While none of the bridges are movable, you get a good idea about the engineering involved in bridges.

The Tower Bridge, in Sacramento California is a neat lift bridge built in 1937 with the counterweights nicely placed inside the superstructure.

      Lift bridges are very cool, unless they lower onto you boat - this happened to a Freighter on the Welland canal once, - and they are all over the place! So get out there and enjoy the huge variety of lift bridges!

 

Lift Bridge