Sunday, February 25, 2018

Mendocino County, California Bridges: Highway 101 Bridge across the Russian River

August 2017 (38.95389-123.10167) Russian River Bridge
We've gone back to Mendocino County to look at bridges we missed during our last trip in August. California built a realignment of Highway 101 in 1933 that included this bridge over the Russian River. We can see in the photo above that the bridge has long (steel girder) approaches on both ends. The main span is a steel through truss bridge but with such a high skew that the portal and sway braces are attached to the previous panels. In the plan view below we can see more clearly how the end panels are cut to accommodate the skewed bracing.
The main span is 245 ft long and the total bridge is 1125 ft long over the Russian River flood plain. The Russian River is the second longest waterway in California with a length of 110 miles. It was originally called the Ashokawna by the First Nation people and then Slavyanka by Russian fur traders in 1817. It's a surprisingly wild river, especially during the winter. Beavers were once hunted along the river and even today 8 ft long sturgeons have been caught in its deeper regions.
The river flows south nearly parallel to Highway 101 causing the bridge to have its high skew. Past our bridge it eventually turns west for about 40 miles before emptying into the Pacific near Jenner. Despite the river being somewhat isolated I counted about 20 major bridges crossing the river including it's forks (the East Russian River) and tributaries (Austin Creek). You can look at some of these interesting bridges on my website or on the Bridgehunter website.
The vertical clearance of the through truss is limited by the cross bracing at the top. The minimum vertical clearance = 15' - 4", which makes the bridge structurally deficient (see photo below). We can also see in the photo below that the road is climbing out of the Alexander Valley and over the Mayacamas Mountains to the north (shown in the background).
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