WOW that's a nice one!
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It would be great if somebody could explain that bridge, basically deck plate girder on top of a truss--that is a pretty unusual structure.
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| Posted by SES on September 3, 2021 | |
Most likely the deck girders originally existed with metal support towers but when the roadway was built, it probably was cheaper to build this smaller trusswork with shorter concrete end supports than to build a much larger and elaborate traditional truss structure for a train to pass thru with much taller and more expensive supports. A simpler and more economical way to modify an existing structure.
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| Posted by SES on September 3, 2021 | |
Considering also this line was a very important route to the Southern Pacific, I also would guess modifying the original structure to be supported by this trusswork would also save a tremendous amount of time for the line to be closed while the bridge was reconstructed. The truss supports could have been built with no interference to the original structure. The trusswork could have been constructed very close to this site. Then the existing girders could have been lifted off, old supports quickly removed and trusswork lifted in place and reset the girders on top.
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Thanks SES, that is a pretty logical suggestion. Upon review, the lacing in the members of the supports at photo right looks to me ca. 1900s-1940s, while the truss members look more 1950s-1970s. Maybe when the plate girders were built the entire road ran under the span under the second locomotive.
The 'we'll build a new support for the existing bridge, to enable the highway' bit fascinated me locally, when they did that for the train track approaches to the Huey P. Long Bridge over the Mississippi River; I think rail service was only disrupted in one or two planned intervals of 24-48 hrs. It was quite an operation to see.
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