Friday, April 30, 2010

Movable Bridges - Spokane Street Swing Bridge (2)

Another view of the Spokane Street Bridge. Note the old bascule railroad bridge in the background. This area is part of a huge port. The Spokane Bridge carries container trucks into the harbor while also allowing container ships through the channel.

The previous bridge restricted access to the channel and so it was replaced with a double leaf swing bridge that can rotate completely out of the way. Each leaf is 450 ft from end to end and the bridge  provides about 350 ft  of channel clearance.

The tower that controls the bridge can be seen on the right side of the photo. Each leaf rests on a 103 inch diameter steel piston. To move the bridge the operator disengages locks that hold the two leafs in place, turns on a pump that raises the two pistons on hydraulic fluid, and then activates two arms that turn the leaves in opposite directions. That was the case until after the 2001 earthquake when one piston was found to be damaged. The City of Seattle had more pistons sitting on the site and replaced the damaged cylinder in a few days. Eventually KPFF, who acted as a sub-consultant to URS, designed a new cylinder that was less likely to suffer fatigue.

A concrete swing bridge is an innovative idea and this attractive bridge won a number of awards.
Creative Commons License
Movable Bridges - Spokane Street Bridge (2) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

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