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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Sunday, February 18, 2018

Shasta County Bridges: Pedestrian Bridge across Big Chico Creek

February 2018 (39.731, -121.844) Big Chico Creek Bridge
I drove to Chico to visit my granddaughter who took me on a tour of Chico State University. Winding its way through campus is the Big Chico Creek with several bridges that carry students to class.
This week's structure is a prefabricated through truss pedestrian bridge made of Corten steel by Big R Bridges out of Greeley, Colorado. I though the red color went nicely with all the trees on campus. There is a sign by the bridge that states the maximum load is 72,000 lbs. That is the load of an AASHTO LRFD HL 93 truck whose three axles are 32 kips, 32 kips, and 8 kips. I would imagine that the allowable pedestrian load is much higher.
The bridge looks pretty strong and it's carrying a large utility load on both overhangs (see photo below). This bridge is a Pratt truss because it carries the load through diagonal members sloping toward the center of the bridge. I count 12 - 8 ft long truss panels.
There is a tab screwed onto the ends of the truss with the vehicle loading (HL-93), a serial number, and the date the bridge was manufactured (January 2016). It's funny they designed this pedestrian bridge for a vehicular load. Maybe in an emergency it must be able to carry a truck load.  Information on when it was placed at the site (and the bridge's name) wasn't available.
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Sunday, February 11, 2018

Monterey County, California Bridges: Pfeiffer Canyon Bridge South of Big Sur (2)

October 2017 (36.239, -121.775) Pfeiffer Canyon Bridge (44 0298)
It was a year ago that I wrote about the landslide that damaged the Pfeiffer Canyon Bridge and the efforts to accelerate construction of the new bridge. The new bridge was completed in October, seven months after the 49 year old bridge was demolished. The old bridge had to be demolished first because the new bridge was build at the same location. A video of the new bridge's construction is available from Caltrans.
In the photo above we can see the superstructure being assembled from behind the abutment. The girders were built with enough camber to allow it to span half the distance before coming to rest on the temporary shoring before being dragged to the opposite abutment.
The replacement bridge is a single span 308 ft long steel girder bridge without piers, which will hopefully prevent future slides from impacting the bridge. Note the walkways (above) needed to allow the bridge to be painted and inspected.
The new bridge cost $24 million and was built by the Golden State Bridge Company in Benicia California. The steel girders were fabricated in Vallejo California. The bridge has a new bridge number (44 0298) and a bridge inspection was done on October 18th, even though the overhangs and abutments were still supported by falsework and the joint seals still needed to be installed (see top and bottom photos).

Sunday, February 4, 2018

Bridges of Mexico: Puente Ticumán across the Rio Yautepec in the State of Morelos

October 2017 (18.7308, -99.11915) Puente Ticumán
Damage to the Puente Ticuman from the  9/19/2017 Mexico Earthquake was reported by GEER Main Team member Prof. Alesandra Morales from the University of Puerto Rico.
She wrote:
Its a  classic embankment failure. The bridge is in good condition. Minor cracking prior to the earthquake.

What the workers told her:
1) Bridge was designed by Japanese Consultants.
2) Bridge was NOT designed for heavy loads.
3) Bridge was being use for heavy loads (farming industry).
4) There's a steel bridge that runs parallel to this one and its the one that is currently being used by the locals (alternate route).
5) They will only fix the entrance/exit to the bridge so people can use it for the moment.
6) A total reconstruction of the bridge will take place next year and they are thinking about using drilled shafts.
7) Lots of bees! 
Alesandra wrote "It appears that the masonry wingwalls failed and the suddenly unrestrained embankment slid down the hill.'
Alesandra's report makes the bridge site sound like an agriculture area but the Google Photo above makes it seem more like a resort! This area near Jojutla had the most serious earthquake damage, mostly related to weak and unstable soil.