Tuesday, May 18, 2010

Movable Bridges - I Street Bridge (2)

A closer look at the I Street Bridge. A swing railroad bridge has stood at this site since 1858. The current double-deck bridge was built in 1911. Note the round pivot pier supporting the swing span.

This bridge is 840 ft long with a 340 ft long swing span.A 34 ft tall boat can pass under it at low tide. Otherwise, the captain must signal to the bridge operator to get through. Boaters need to check with the US Coast Guard when planning a trip to find out the bridge's hours of operation,

Swing bridges, and especially swing railroad bridges are more complicated than bascule or lift bridges. Not only do they need locking devices that open and close, but the railroad tracks need to be retracted to open the bridge and extended for trains to pass. There are also devices to help the bridge resist wind (and seismic) loads.

This is one of the largest center bearing swing bridges ever built. It weighs about 6800 kips. At the turn of the 19th century, such big swing bridges had rim bearings with rollers along the perimeter. When this large bridge was successfully built and operated with a center bearing, no one wanted to go through the trouble of fabricating the conical rollers that supported a rim bearing swing bridge and they were no longer built.
Creative Commons License
Movable Bridges - I Street Bridge (2) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

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