Friday, August 19, 2016

Lake Street Bridge

3D Satellite
(Bridge HunterHistoric BridgesChicago Loop Bridges)

Lake Street Bridge is the double-deck bridge in the foreground. I included more than the bridge in this view because I think the railroad tracks help date how old Google images are. I want to check if those air rights are still unused.

This bridge was built in 1916 because the Federal Government declared the center pier of swing bridges to be a navigation hazard and because Chicago bridge engineers were successful in perfecting the fixed trunnion bascule bridge. What was an adequate width for wood schooners became marginal for iron hulls and ridiculously narrow for steel hulls. The original design was going to use a lift span as was customary with railroad tracks. Though lift spans are considered OK for industrial areas such as the Calumet River or even more downstream on the South Branch,  a lift bridge was considered too ugly for the heart of downtown. Thus this was the first double-decker fixed trunnion bascule bridge ever designed and built. The Wells Street Bridge was a refinement of this design.
Jeff Nichols -> Forgotten Chicago
Lake Street bridge, 1909. Chicago History Museum, DN-0007256
Chicago History Museum via DNAinfo, 1909

Chicago History Museum via DNAinfo,  March 6, 1916
[This must have been when they lowered the leaves of the new trunnion bridge for the first time. The leaves were built in the upright position while the swing bridge continued to operate so that streetcar traffic would not be interrupted. Then they stopped service, turned the swing bridge, cut out the middle, and lowered the leaves into the hole in the swing bridge to resume service.]

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