Sunday, March 25, 2018

Mendocino County Bridges: Route 271 Bridges across Big Dann and Cedar Creek

2000 (39.84861-123.70222) Cedar Creek Bridge
When State Highway 101 was completed, old State Route 271 was relinquished to the county. However local residents continued to use the Big Dann (10 0030) and Cedar Creek (10 0029) bridges (on 271) to get to and from their homes. The cost to seismically retrofit these big bridges would have been millions of dollars and so the residents agreed to the installation of seismic gates instead. When an earthquake occurs, the ground shaking will close the gates, preventing people from driving onto the bridges.

Sunday, March 18, 2018

Southwest Eighth Street Pedestrian Bridge Collapse in Miami, Florida

Like many of you, I was shocked and saddened by the news that a pedestrian bridge collapsed while it was being constructed across Southwest Eighth Street in Miami, Florida. As a bridge engineer I'm always worried about making a mistake that could result in similar damage.
This bridge was being built using accelerated bridge construction (ABC) techniques, which are meant to get bridges built faster and more safely. Hopefully we'll learn some lessons from this collapse that will make bridge design and construction even safer in the future.

Sunday, March 11, 2018

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.

Sunday, March 4, 2018

Mendocino County Bridges: Philo Greenwood Road Bridge across the Navarro River

August 2017 (39.08580-123.48450) Philo Greenwood Road Bridge
Continuing northwest from last week's Russian River Bridge, we arrived at the Philo Greenwood Road Bridge across the Navarro River. This is an open spandrel arch bridge (with timber approaches) that was built in 1951. The arch span is 130 ft long and the entire structure is 352 ft long.
The twin arches are founded in rock on each river bank and support a thin deck on spandrel columns. This is a local agency bridge (10C0032) supporting a county road.
The Navarro River is 28 miles long and flows northwest through the Coastal Range to the Pacific. Philo is the name of a town and Greenwood is the name of a ridge that are connected by the road.
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