Mendocino County Bridges: Confusion Hill Bridges Carrying Highway 101 across the South Fork of the Eel River

August 2010 (39.92088, -123.76359) Confusion Hill Bridges

The Confusion Hill Bridges are two structures that carry Highway 101 across the South Fork of the Eel River in Mendocino County. The bridges were designed and constructed to avoid a massive landslide on the south bank of the river.  The North Bridge (10 0299) was completed in July of 2009 and the South Bridge (10 0300) was completed in September 2009 and the bypass was opened in October of 2009.

The North Bridge is a 581 ft long continuous prestressed box girder bridge on sloping single column bents (see top photo). This shorter bridge was built using the traditional method of supporting the wet concrete and rebar on falsework.

The South Bridge is a long three span continuous prestressed box girder bridge on vertical single column bents. It has a total length of 1239 ft (348 ft, 571 ft, 436 ft). It was built segmentally using cantilever construction (where the weight of the cured concrete supports the cantilevered spans).

Both bridges were designed by Caltrans engineers and built by Finley Engineering Group out of Tallahassee, Florida and by MCM Construction of California.

Marin County, California Bridges: San Rafael Viaduct

June 2010 (37.9686, -122.5208) San Rafael Viaduct

Just north of the S101-E580 Connector (on 101) is the San Rafael Viaduct (27-0035L/R/S), three long-span prestressed concrete box girder bridges that were built in 1965 and heavily retrofit in 1993.

The parallel bridges include column casings and link beams that can form plastic hinges and protect the columns during earthquakes.

This ends our study of the bridges in Marin County, a small but affluent region in California with an intense (and often gridlocked) network of transportation infrastructure along it's east coast and with very little infrastructure along it's rugged west coast.

Los Angeles County, California Bridges: I-105/I-710 Interchange across the Los Angeles River

August 1999 (33.9103 Degrees, -118.1805 Degrees) Los Angeles River Bridges 

Continuing downstream to the big I-105 (Century Freeway)/I-710 (Long Beach Freeway) Interchange (53 2419) across the Los Angeles River.  I remember when it was built because I designed part of the I-105/I-110 interchange west of here. It took the right-of-way agents several years to acquire all the land to build a new freeway all the way across Los Angeles.

The transmission lines may be finally ending because I remember a substation at this interchange. We're still about 10 miles north of the river 's mouth at San Pedro Bay.

Los Angeles County, California Bridges: I-105/I-710 Interchange across the Los Angeles River by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

Shasta County, California Bridges: Boulder Creek Bridges (1)

April 2015 (41.01611 Degrees, -122.40611 Degrees) Boulder Creek Bridges

Today's photo is of the Interstate 5 Bridges (06 0193L/R) towering over the Highland Lakes Road Bridge (06C0349).  I'd like to take dramatic photos of several bridges together, but it's hard when they're at different angles and in dense vegetation. I bought a drone to take better shots from above but I'm afraid I don't have the skills to prevent the plane from crashing into traffic.

Shasta County, California Bridges: Boulder Creek Bridges (1) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

Shasta County, California Bridges: I-5 Bridges across the Sacramento River

April 2015 (41.0111 Degrees, -122.4094 Degrees) Sacramento River Bridges

As I mentioned yesterday, Interstate 5 crosses the Sacramento River twice as it makes a big loop around some foothills. We are traveling into a mountainous region with Mount Shasta dominating the landscape to the north. Consequently, the Sacramento River Bridges and Overheads (06 0192L/R) are on very tall single column bents as they cross over the river and railroad. These bridges have four span prestressed cast-in-place concrete box girder superstructures and they were built in 1989. They're 863 ft long with a 240 ft long span over the railroad and river. The bridge soffit is 70 ft above the tracks. The normally wide Sacramento River looks like a meandering creek at this location.

Shasta County, California Bridges: I-5 Bridges across the Sacramento River by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

San Francisco County, California Bridges: Alemany Interchange

December 1998 (37.7352 Degrees, -122.4094 Degrees) Alemany Interchange

South of the Central Freeway Viaduct, Highway 101 and 280 come together at the Alemany Maze (34 0070). This  complicated interchange is composed of short stiff piers, big strong piers, and tall flexible piers. An innovative retrofit was developed that used isolation to make the different substructure elements move together during the design earthquake. The stiff members had flexible isolators that allowed the superstructure to displace. The strong members used isolators to prevent the columns from damaging the weaker bent caps. The flexible members were free to move without causing damage to stiff or weak elements.

San Francisco County, California Bridges: Alemany Interchange by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

San Francisco County, California Bridges: West Approach to the Bay Bridge

July 2014 (37.78139 Degrees, -122.39750 Degrees) West Approach

Today's set of photos show the different bridges we cross as we head north on the I-80 Bayshore Viaduct (34 0126L/R) towards the San Francisco-Oakland Bay Bridge.

After the Terminal Separation and Embarcadero Viaduct were removed following the 1989 Loma Prieta Earthquake, the West Approach to the Bay Bridge became a combination of retrofitted structures and brand new ramps all designed to stay in service following a large earthquake.

Several different ramps come together (supported on big outrigger bents) to become the top and bottom decks of the West Bay Bridge, which can be seen between the columns in the photo below. More information on the project to rebuild the West Approach can be viewed on the Bay Bridge Info Website.

San Francisco County, California Bridges: West Approach to the Bay Bridge by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.