Saturday, May 22, 2010

Movable Bridges - Meridian Bridge

This is the last movable bridge I have photos of on the Sacramento River. However, there are a few more movable bridges up north that I hope to photograph (maybe during the summer).

Bridge engineers are faced with a challenge providing a big enough channel opening with a swing bridge. Because the support is in the center, it's difficult to make the cantilever spans on each side large enough for ships to pass. We saw that the Spokane Street Bridge (April 28th and 29th) has a swing span on each side of the channel so that a very large opening can be created. The other swing bridges we looked at had truss superstructures to provide long stiff cantilever spans. The Meridian Bridge solves the problem in a different way, with a central tower and a cable stays to support the cantilever spans.

This bridge carries State Route 20 across the Sacramento River a little south of Colusa and a little west of Marysville. It was built in the 1970s (and along with the Spokane Street Bridge) provides a good example of how engineers can develop new solutions to address some of the disadvantages inherent with swing bridges. The tower is 50 ft tall and the leaves are about 180 ft long, providing a suitable opening for ships to pass.

We'll take a closer look at this interesting bridge tomorrow.
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