Monday, December 31, 2012

Nevada County, California's Bridges: Washington Road Bridge across the South Yuba River

December 2012 (39.3605 Degrees, -120.7946 Degrees) Washington Road Bridge
Driving back from the Maybert Bridge we crossed over this two-span bridge with a round soffit just before the town of Washington. The soffit was so wet and covered with moss, that I thought they must have purposely made it round to reduce drag when the South Yuba River overflows it's banks.

The Washington Road Bridge (17C0056) is a two span 237.9 ft long RC box girder bridge built in 1971. The bridge is in pretty good condition (sufficiency rating of 81 out of 100) but it's in danger of flooding due to the river overflowing or changing it's banks. Bridge crews must frequently add riprap around the pier and abutments to protect the foundations.
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Nevada County, California's Bridges: Washington Road Bridge across the South Yuba River by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 License.

Sunday, December 30, 2012

Nevada County, California's Bridges: Maybert Road over Canyon Creek

December 2012 (39.3618 Degrees, -120.7503 Degrees) Maybert Road Bridge
There are several of these short, single span, half-hipped Pratt pony truss bridges over creeks in Nevada County. Getting to this bridge required a drive through deep snow east of Nevada City (on State Route 20) and then down Maybert Road through the town of Washington in what was once gold country. The bridge crosses Canyon Creek just before it flows over a dam into the South Fork of the Yuba River.
The Maybert Road Bridge was built in 1915 according to the Bridgehunter (my copy of 'Historic Highway Bridges of California' gives the date as 1895).  It's structurally deficient (scoring 5.0 out of 100 during the last inspection). If it ever had a steel railing it's long gone. Timber stringers are supported by steel floor beams that extend past the deck and are attached to diagonal tension members and latticed, vertical  members. The bridge is scheduled for replacement in 2014. Average daily traffic is 100 vehicles, which justifies the construction cost of $400,000 or about $200 per square foot.
Based on the evidence in the Bridgehunter's blog, 1895 seems like a more reasonable date since a plaque near the bridge says the town of Ormonde was established there in 1887 (and the town of Maybeck a few years before) but all the mining settlements were abandoned by 1897. Perhaps the original bridge was built in 1895 and a replacement was set on the same abutments in 1915? This was the furthest upstream along the South Yuba River where there was mining and it yielded $17 million in gold before it was played out.
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Saturday, December 29, 2012

Nevada County, California Bridges: Dog Bar Road Bridge across the Bear River

December 2012 (39.0627 Degrees, -121.0030 Degrees) Dog Bar Road Bridge
On the border between Placer and Nevada Counties, across the Bear River, is the Dog Bar Road Bridge (17C0031). It is a four span steel girder bridge that was built in 1935 and rehabilitated in 2000 (the barrier rail looks new).

For a single lane bridge it carries a lot of traffic (over 1000 vehicles a day). While I was photographing the bridge, groups of cyclists rode by and people living in the hills drove across the bridge in pickup trucks.

Nothing very remarkable about this bridge other than the tall pier wall in the middle of the river.
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Friday, December 28, 2012

Nevada County, California Bridges: Edwards Bridge across the South Yuba River

December 2012 (39.3302 Degrees, -120.9843 Degrees) Edwards Bridge
Unlike the previously studied Purdon Bridge, the Edwards Bridge still has it's original steel lattice railing. The 114 ft long arch span is made entirely of triangular truss segments. Its a delicate little structure that was built in 1904 by the American Bridge Company.
This bridge is another early river crossing that carries Bloomfield Road over the South Fork of the Yuba River (I don't know why it's called Edwards Crossing). It's a three-pinned deck arch, similar to the Pine Street (Gault) Bridge we recently looked at in Nevada City. More information is available from the Bridgehunter.
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Thursday, December 27, 2012

Nevada County, California Bridges: Purdon Bridge across the South Yuba River (2)

December 2012 (39.3278 Degrees, -121.0465 Degrees) Purdon Bridge
The 145 ft long main span of the Purdon Bridge (17C0024) is supported on four concrete filled pipe piles. The approach spans are on steel stringers while the main span is on timber stringers. This 117 year old bridge is eligible for the National Register of Historic Places but it's structurally deficient (scoring only 16.2 out of 100) and the current recommendation is for bridge replacement. The truss members are covered in rust but fortunately, the bridge only carries 47 vehicles a day. It currently has a load rating of 4.4 tons, which seems high. I imagine that it's up to Nevada County to rehabilitate and preserve this historic bridge.
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Wednesday, December 26, 2012

Nevada County, California Bridges: Purdon Bridge across the South Yuba River (1)

December 2012 (39.3278 Degrees, -121.0465 Degrees) Purdon Bridge
Traveling to the east from Bridgeport we eventually reached the Purdon Bridge over the South Fork of the Yuba River. This structure is reputed to be the only half-through truss bridge in California. However, I seem to recall the Ponderosa Way Bridge and several other bridges had their decks supported at mid-height between the top and bottom chords.
The Purdon Bridge is a pin-connected Pratt truss built by the Oakland-based Cotton Brothers in 1895, who were important builders of steel truss bridges in the late 19th and early 20th centuries. This bridge replaced several timber crossings that had been washed away in floods. It was a major link on the road from Nevada City to points north. Today it is road bridge and also part of a hiking trail through the South Yuba River State Park.

I wonder how much of the original bridge is still standing? The truss is authentic but the deck and railing appear to be recently constructed. Also, the bridge is supported on driven pipe piles, which I don't remember seeing on too many 19th century bridges. The portal frame is quite lovely, but the plaque on top is missing. However another plaque from 'E Clampus Vitus' is mounted on a rusted truss member.

We'll take a look under the bridge tomorrow.
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Tuesday, December 25, 2012

Nevada County, California Bridges: Bridgeport Covered Bridge across the South Yuba River (3)

December 2012 (39.2927 Degrees, -121.1949 Degrees) Bridgeport Covered Bridge
The Bridgeport Bridge was owned by the Virginia Turnpike Company, which provided a toll road beween the Comstock Lode and Nevada County goldmines. The company owned 14 miles of road that carried up to 100 wagons a day before it was closed in 1901. In 1863 the company collected $20,915.45 in tolls. The cost to use the road in 1862 included:
      • 8 horse, mule, or ox team (each way) - $6.00
      • 6 horse, mule, or ox team (each way) - $5.50
      • 4 horse, mule, or ox team (each way) - $4.00
      • 2 horse, mule, or ox team (each way) - $2.50
      • 1 horse, mule, or ox team (each way) -  $1.75
      • 2 horse buggy (each way) - $1.50
      • 1 horse buggy (each way) - $1.00
      • Horseman - $0.50
      • Footman - $0.25
      • Loose stock - $0.10
      • Hogs and sheep - $0.05
The Bridgeport Covered Bridge survived due to the extraordinary efforts of many people over the years. The original bridge was washed away by a flood in 1862 and was rebuilt in the same year. There was a great fire in 1988 that destroyed dozens of homes in Nevada County and came within 200 feet of the bridge before it was stopped by firefighters. Another flood in 1997 brought the flood waters up to the same level as 1862. In the restoration that followed the flood, the bridge was brought back to its original state (excluding the rail and windows).
The bridge was closed to pedestrian and vehicular traffic on October 21, 2011. An inspection showed it needed repairs before it could be reopened. It will remain closed pending a detailed engineering report, which will help the county decide on the bridge's future.
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Nevada County, California Bridges: Bridgeport Covered Bridge across the South Yuba River (3) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 License.

Monday, December 24, 2012

Nevada County, California Bridges: Bridgeport Covered Bridge across the South Yuba River (2)

December 2012 (39.2927 Degrees, -121.1949 Degrees) Bridgeport Covered Bridge
A look inside the Bridgeport Covered Bridge. It's called a Burr Arch Truss (patented by Theodore Burr in 1817) because the 'X' members of the Howe truss keep the bridge rigid while the timber arch carries the vertical load. However, computer models suggest that it is actually the truss carrying the load while the arch maintains stability. Whatever the case, the arch/truss structure can carry a longer, heavier span than either the truss or the arch bridge could carry alone. The structural members are Douglas Fir (and steel rods) while the 27,000 shingles are made from Sugar Pine.

The bridge model in the nearby museum shows the truss supported on the top of the stone abutments while the arch springs from the bottom of the abutments.
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Sunday, December 23, 2012

Nevada County, California Bridges: Bridgeport Covered Bridge across the South Yuba River (1)

December 2012 (39.2927 Degrees, -121.1949 Degrees) Bridgeport Covered Bridge
Continuing west on Pleasant Valley Road we come to another pair of old and new bridges. What makes this pairing interesting is that the covered bridge (built in 1862) spans the South Fork of the Yuba River in a single span while the modern reinforced concrete bridge requires a center pier to cross the river.

The Bridgeport Covered Bridge is an odd combination of an arch and a truss bridge with a 230 ft main span. It was designed by David Isaac Johnwood for the Virginia Turnpike Company with lumber from his sawmill 30 miles away. It is one of only nine surviving covered bridges in California and the longest single span covered bridge in the United States.
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Saturday, December 22, 2012

Nevada County, California Bridges: South Yuba River Bridges (4)

December 2012 (39.2977 Degrees, -121.0890 Degrees) South Yuba River Bridges
The new South Yuba River Bridge is a modern variant of the concrete arch. Probably it was meant to contrast with the old South Yuba River Bridge sitting beside it. It was designed by Ade Akinsanya and Paul Snyder from Caltrans Design Branch 6 with some help from Bridge Aesthetics. They were fortunate that this is an area of low seismicity since the small diameter horizontal curve and unbalanced columns wouldn't do too well for a large lateral force.

You can see that the slab superstructure in Section B-B and the precast girder superstructure in Section C-C have a deep exterior girder to match the depth of the box girder in Section A-A of the main span. Caltrans bridge engineers get tired of designing the same thing all the time so management usually lets them try something new when the situation allows.
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Friday, December 21, 2012

Nevada County, California Bridges: South Yuba River Bridges (3)


December 2012 (39.2977 Degrees, -121.0890 Degrees) South Yuba River Bridges
The old South Yuba River Crossing is an open spandrel deck arch bridge. It has tiny abutments, short approach spans, and massive fluted pier walls that support the arch ribs. It looks like the rocks under the arch supports have eroded.

Spandrel columns are at the ends of the arch and shear walls are in the center. Drop caps support the deck and you can see the outline and grain of the falsework on the underside of the deck. Ballustrade railings on top complete a very classical look to this old, reinforced concrete arch that was well worth preserving.
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Thursday, December 20, 2012

Nevada County, California Bridges: South Yuba River Bridges (2)

December 2012 (39.2977 Degrees, -121.0890 Degrees) South Yuba River Bridges
The South Yuba River Pedestrian Bridge is located where rocks and sediment have accumulated along the south river bank. There are so many boulders in this part of the river that I'm surprised the kayakers can navigate through it.

This was an early success story for the preservation of an historic bridge. Since the bridge was already in a state park and the new highway bridge was being built downstream, it was easy to preserve the old bridge for pedestrian use.

There are four methods used for bridge preservation:
  1. Repair the bridge for continued use.
  2. Bypass and preserve the bridge.
  3. Move the bridge to a site with lighter or non-vehicular traffic.
  4. Rehabilitate the bridge while maintaining it's historic character.
The Pine Street (Gault) Bridge that we previously studied was not preserved. Perhaps Nevada City felt they had already preserved enough historic parts of the city and so they just build a replica of the old bridge. I believe the only part of the bridge that was preserved was the steel railing.
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Wednesday, December 19, 2012

Nevada County, California Bridges: South Yuba River Bridges (1)

December 2012 (39.2977 Degrees, -121.0890 Degrees) South Yuba River Bridges
State Route 49 goes sharply west just north of Nevada City and then crosses the South Fork of the Yuba River on a new (1993) prestressed concrete bridge. The original (1922) reinforced concrete arch bridge has been turned into a footbridge and part of a hiking trail in the South Yuba River State Park.
Just as the North Fork of the American River dominates many aspects of life in Placer County so the South Fork of the Yuba River dominates the west side of Nevada County (west of the Sierra Nevada Mountains).

We'll take a closer look at the old and new bridges in the next few blogs.
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Tuesday, December 18, 2012

Nevada County, California Bridges: Pine Street Bridge across Deer Creek (4)


December 2012 (39.2609 Degrees, -121.0193 Degrees) Pine Street Bridge
I managed to stitch together this panorama of the Pine Street Bridge. If  you look closely you can see a couple roofs of houses behind the trees, but otherwise it looks like the bridge is in the middle of the forest instead of in the middle of a small city. I'm surprised that they are allowed to drain water from the bridge deck into Deer Creek. Much more information on the history of this bridge site can be obtained from the Nevada County Transportation Newsletter , from the Library of Congress, and from the Bridgehunter Blog. However, the last two websites don't seem aware that the current Pine Street (Gault) Bridge is just a replica of the bridge that was built in 1903.
Perhaps part of the confusion stems from the bridge plaque, which refers to a third span but really means the third bridge at this site.
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Monday, December 17, 2012

Nevada County, California Bridges: Pine Street Bridge across Deer Creek (3)

December 2012 (39.2609 Degrees, -121.0193 Degrees) Pine Street Bridge
It's always surprising to me that a bridge can seem part of the urban environment from the deck while appearing part of the wilderness from underneath.  Also it's surprising how a site can appear to be untouched by older cultures, but if you look more closely you can find the detritus of thousands of years of human habitation.

The Pine Street Bridge was built in 1996 to look like the previous bridge that was built in 1903.

In some ways this bridge does look like the older structure. The lacing of the members looks the same (see comparison of new and old bridges below). Also, both bridges are three pinned steel truss arches.
However, the foundations are huge on the new bridge (see below).  The rivets on the old bridge have been replaced with bolt heads made to look like rivets on the new bridge. Also, the new bridge is made from Cor-Ten steel while the existing bridge is made from carefully painted high-carbon steel.
It seems a little depressing that the city was obligated to make a new bridge look like an old bridge. Apparently it's so important for Nevada City to appear old that it is no longer allowed to grow. 

In Jerusalem, which is a much older city, the buildings must be constructed of limestone but they can still build new bridges like the ones by Calatrava.
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Sunday, December 16, 2012

Nevada County, California Bridges: Pine Street Bridge across Deer Creek (2)

December 2012 (39.2609 Degrees, -121.0193 Degrees) Pine Street Bridge
A reliable crossing over Deer Creek was a necessity for the residents of Nevada City (as it had been for the residents of Ustamah, the Maidu village that was at this site before the Gold Rush of 1849). Originally, log bridges at creek level were used but they were washed away by the spring floods. In 1862 Nevada City hired Andrew S. Hallidie (a 25 year-old engineer who went on to build San Francisco's cable car system) to construct a one-lane suspension bridge at Pine Street (see photo below). This raised the bridge surface to a safer level above Deer Creek (photos from the Library of Congress).
In 1903 after automobiles began to be used, the suspension bridge was replaced by a truss arch bridge designed by the American Bridge Company and built by Clark and Henery, a Stockton, California contracting firm (see photo below).
By the 1990s, the arch bridge had deteriorated and it was replaced with a very similar bridge designed by Foster Engineering of Orinda, California and built by West Coast Bridge Inc. of Benicia, California.
So the current Pine Street (Gault) Bridge is a new bridge built to resemble a very old bridge. We'll take a look under the deck tomorrow.
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