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| November 2012 (39.123 Degrees, -120.940 Degrees) Long Ravine RR Trestle Bridge |
Older photos (from 1870) show a long timber trestle bridge, which was replaced with embankments and an 878 ft long steel viaduct, perhaps when the expressway was built. It must have been cheaper to build a long timber trestle bridge than a long embankment in the 19th century.
Placer County, California Bridges: Long Ravine RR Trestle across I-80 by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 License.
On main line railroads, early wood trestles were typically replaced by steel trestles relatively soon, and in many cases those trestles were replaced again in the early decades of the 20th century, well before multi-lane highways were constructed.
ReplyDeleteIn bridges such as the recent Auburn posts and this one, the original trestle structure is still present as the shallow girders supporting the track. The truss (Auburn) and deep girder (here) spans replaced the trestle bents that would have obstructed the highway being constructed underneath. The long spans were most likely built under the trestle as trains continued to pass overhead, with the load then transferred to the new span and the bents removed.
I particularly like the 'covered bridge' segment of the wood structure - covered bridges are usually through trusses with a roof over the roadway as well as the truss [some through trusses had only the trusses sheathed, with skinny 'roofs' on them, but the roadway open to the sky] but this is a deck truss with the 'roof' under the railroad track. Sheathed bents, too. Nice.
Wooden trusses were not only cheaper, but also faster to build. Many were buried by fill [delivered by train] after regular railway operations began. Starting revenue operations as quickly as possible was typically a high priority, and with a working railway, fill could be brought more cheaply from greater distances.