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Bridge Types |
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The project will soon be at the point of deciding what type of bridge the replacement structure
should be. In a city of bridges, choosing a new bridge design is a major decision that will have
a lasting impact.
There are three bridge types currently under consideration that are possible with the alignment chosen
in the preferred alternative. The alignment will be approximately 15 feet south of the existing Tacoma
Street centerline to allow for continuous traffic flow at the crossing throughout construction.
Keeping the bridge open to traffic determines the construction approach, which eliminates some bridge
types from consideration.
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Click on the bridge type headings below, to view more information and the bridge type renderings.
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The renderings of the bridge types are for illustrative purposes only - they are not meant to depict
the final designs and they do not include design details like color, texture, lighting, etc.
Additionally, the interchange with Hwy. 43 will require that the bridge deck be wider on the west end
of the bridge to give vehicles enough space to queue before turning. This additional deck width is
not illustrated in the renderings.
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Clean, simple, modern, and cost-effective to construct and maintain, this is a common bridge type.
Its architectural detail is generally concerned with the shapes of box girders and piers, as well
as with slopes, shadow lines, and textures. This design is very flexible in accommodating varying
deck widths and can easily be stage-constructed in halves while maintaining traffic access (only
for Yellow South alignment). The I-205 Glen Jackson Bridge over the Columbia River is a box girder
design.
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Although basically a box girder, the unique look is achieved by the "Y"-shaped piers supporting the spans.
Additional architectural effects can be achieved with color, texture, and shadow. This bridge design is
moderately priced, while still offering a high level of architectural interest. It can also be
stage-constructed next to the existing Sellwood Bridge (only for Yellow South alignment). This bridge
type is similar to the Alsea Bay Bridge in Waldport, Oregon and would be a new design in Portland.
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The deck arch is a classical form of bridge architecture, as demonstrated in southwest Portland's Vista Bridge.
Made of concrete or steel, this bridge type offers opportunity for additional detail in color, texture, and shadow.
This design works well with varying bridge deck widths and construction could be staged adjacent to the existing
Sellwood Bridge (Yellow South alignment only).
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During the fall of 2007, a Bridge Type Working Group of local bridge experts recommended six
replacement bridge options for further consideration. The Community Task Force and Policy
Advisory Group weighed public input from an online survey and November 2007 open house before
selecting which bridge types to be evaluated in the Draft Environmental Impact Statement (Draft
EIS). The following bridge types were considered.
Click on the bridge type headings below, to view more information and the bridge type renderings.
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Constructed of steel or concrete, the through arch design is similar to the Fremont Bridge and the
West Linn Bridge. The striking design provides an iconic gateway presence, but the arches and hangers
require more long-term maintenance. This option does not work as well for staging construction next
to the existing Sellwood Bridge, nor is it well suited for a deck width that varies to accommodate
the needs of the west end interchange.
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The stress-ribbon bridge type is not used in Portland, so this type offers the option for a unique and
signature bridge. A stress-ribbon bridge has been built in Grants Pass, Oregon for bicycle and pedestrian use.
This bridge type is only available for Alternative A and would be used
for the bicycle/pedestrian only bridge while the existing bridge would be rehabilitated for vehicle traffic.
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Perhaps the most dramatic of the range of bridge types, the cable-stayed bridge design features tall pylons with
steel cables supporting the upper deck. The design allows for a more slender deck than the concrete box girder
design. The visual impact comes from the tall pylons extending hundreds of feet above the surface of the river.
Costlier to construct and maintain than the other bridge types, this design also does not work as well for staging
construction next to the existing Sellwood Bridge, but it is well suited to carrying a double deck. This would be
a new bridge design in Portland.
This bridge type would be used for the bicycle/pedestrian only bridge while the
existing bridge would be rehabilitated for vehicle traffic.
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