Sunday, August 13, 2017

Willamette River Crossings: Marion Street Bridge in Salem, Oregon

July 2017 (44.94556-123.04250) Marion Street Bridge
A hundred yards south of last week's Union Street Railway Bridge is the westbound Marion Street (I-22) Highway Bridge. This bridge is 2400 ft long and 56 ft wide with a steel plate girder superstructure. It was the longest plate girder bridge west of the Mississippi when it was built (in 1952).
The bridge's most unusual feature is that it's supported on pier walls having gothic arch openings. Gothic arch shapes were also used on the nearby Independence Bridge and in some of the arch bridges by Conde McCullough along the Oregon coast. The designer of the Marion Street Bridge, Glenn S. Paxson succeeded McCullough as Oregon's Chief Bridge Engineer and may have used the arches as a tribute to his old boss.
Before this bridge was built, all the traffic across the Willamette was carried on the adjacent Center Street Bridge. In fact, looking at the construction photo below (courtesy of the City of Salem), it appears that this bridge originally had only a single pier at each support (it was widened in the 1980s). That explains why the steel plate girders continue along the approaches on the original bridge but have been switched to concrete for the approaches of the widening (see photo above).
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Sunday, August 6, 2017

Willamette River Crossings: Union Street Bridge in Salem, Oregon

July 2017 (44.947, -123.0418) Union Street Railroad Bridge
Continuing downstream along the Willamette River we arrived at the Union Street Railroad Bridge in Salem, Oregon. This bridge (like last week's Van Buren Street Bridge) is from 1913 and was built by the Southern Pacific Railroad. It changed hands several times before it was finally sold by the Union Pacific Railroad to the City of Salem in 2003.  The bridge was added to the National Register of Historic Places in 2006 and converted to a pedestrian and bicycle bridge in 2009.
This structure is a vertical lift bridge that uses a patented system developed by the designers Waddel and Harrington. The top of the towers are 65 ft above the trusses for a total height of about 100 ft. The towers stopped working in the 1980s and the mechanism (and operator's house) was removed soon afterwards (see bottom photo).
This longitudinally asymmetric five span bridge sits on concrete piers that were designed to be high enough to keep the track five feet above the highest recorded flood water on the Willamette. There is a 134 ft long lift span (shown in photo below) and four Pratt truss spans for total length of 755 feet. There is also an 850 ft long timber trestle on the west end.
This railroad bridge (which carried it's last train in the 1990's) underwent considerable modification before it began carrying pedestrians. Lead based paint, ballast and the track all had to be removed. Besides being redesigned as a pedestrian bridge, it was also redesigned to carry emergency vehicles.
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Sunday, July 30, 2017

Willamette River Crossings: Van Buren Street Bridge in Corvallis, Oregon

July 2017 (44.5655, -123.2566) Van Buren Street Bridge
I recently flew to Corvallis to attend a meeting on bridge design criteria for tsunami loads. Since I was going to be in Oregon, I brought my camera to photograph some of the bridges across the Willamette River. I had previously photographed Willamette River Crossings during a previous visit in 2009 and I thought I'd add a few bridges that I had missed during that visit.
The main body of the Willamette River is 187 miles long and flows north through Oregon into the Columbia River. The Van Buren Street Bridge is a multi-span truss bridge with timber approaches and a swing span near the east bank of the river. This bridge is remarkable in a number of ways. It is the first bridge built in Corvallis to span across the Willamette (in 1913). Despite it's age, it continues to carry heavy truck traffic. It's also Oregon's last remaining movable truss bridge with pinned connections.
The Van Buren Street Bridge is 708 ft long and carries one lane of traffic east across the Willamette (the nearby Harrison Street Bridge carries the westbound traffic). There is also a six ft wide wooden walkway on the south side of the bridge. Starting from the east end, the bridge is composed of a long timber approach (not shown), then a pony truss span, then the Pratt through truss swing span, then a long Parker through truss span, and finally three steel girder spans (that replaced the original pony truss) and more timber approach spans (not shown) at the east end of the bridge. The main spans are supported on concrete piers.
The bridge is owned by the Oregon DOT and the chief bridge engineer told me the bridge was recently strengthened but they plan to eventually replace it (although the replacement isn't currently in the budget). The old bridge will either remain in place (as a pedestrian and bike bridge) or it will be moved to a park. The east approach spans are shown below.
The existing bridge was fabricated in Portland and then shipped down to Corvallis where it was reassembled. The swing span required six people to turn a long wooden paddle that was inserted through the deck into a key that engaged a small gear that rotated one of two large gears that turned the bridge (one gear opened it fast and the other opened it more slowly). The last time the swing span was opened was in 1960.
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