| |
- approach
-
The part of the bridge that carries traffic
from the land to the main parts of the bridge. Downtown
bridges are chararacterized by approaches that clear several
blocks of cityscape before merging with the main spans,
served by freeway-style ramps that connect them to several
surrounding street.
-
- arch
bridge
- A bridge whose main support structure is
an arch, such as the Fremont. Additionally, the bridge may
be termed a through arch, which is simply one where
the roadway appears to go through the arch (again the Fremont
is a good example of this).
-
- Bascule
bridge
- A type of movable, or draw, bridge.
The word Bascule is from the French for seesaw,
which describes the part of the bridge that moves. Three
of Portland's bridges are Bascules; the Broadway, the Burnside,
and the Morrison.
This type of bridge allows the roadway
to tilt up and out of the way of river traffic, using counterweights
as the counterbalance.
There are two main types of Bascule in evidence in Portland.
The Broadway bridge is an example of the Rall type
Bascule, in which the counterweights are on the outside
of the bridge move back and forth on bull wheels. The Morrison
and Burnside are Strauss Bascules, where the counterweights
are hidden within the bridge supports. Strauss Bascules
operate in a speedier fashion than the Rall design.
-
- cantilever
bridge
- Acantilever is a bracket or arm
that juts out. Cantilever bridges are made up of two such
brackets. A diving board is a good example of a cantilever
that is anchored at one end and free at the other. The cantilever
design provides the strength and rigidity called for in
heavy frieght and railway bridges, provides economy of materials
and simplifies construction. The Marquam and Ross Island
bridges are Portland's two major cantilever bridges.
-
- continuous
span bridge
- A bridge that extends as one piece over
multiple supports. The Sellwood Bridge is an example of
a continuous-span truss bridge, with four spans, it has
been described as a 'log on five supports'.
-
- double-leaf
Bascule span
- A draw span that comprises two Bascule
leaves, such as the Broadway, Burnside, and Morrison bridges.
-
- fixed-span
bridge
- A bridge without a movable, or draw, span.
-
- lift
span
- The part of a movable-span (or drawbridge)
that opens to allow river traffic. Also called the draw-span.
-
- main
span
- The longes span in a multi-span bridge
and located between the bridge's main piers or towers (supports).
Bridges typically compared using main-span lengths, which
do not account for the length of the entire bridge or its
approaches.
-
- Men Below, Please
Don't Throw
- A sign once seen on the approaches to almost
all Portland's traffic bridges, now only seen on the Sellwood.
Reminds pedestrians that Portland's bridge approaches typically
go over buildings and other streets, so it's prudent not
to toss refuse of any type down so as not to injure other
pedestrians near the facility.
-
- movable
bridge
- Bridge with a section that moves out of
the way of river traffic to allow passage. Also called draw
bridges. Of the three types of movable bridges, two
are found in Portland's traffic bridge inventory. Bascule
bridges include the Morrison, Broadway, and Burnside. Vertical
lift is represented by the Hawthorne, and is obvious
by description.
-
- pier
- A bridge support that is in the water.
Those on the land are called bents.
-
- precursor
span
- Many of Portland's bridges were not the
original spans at those locations, but rather had one or
two predecessors in the same location. Usually these bridges
were built of materials that were state-of-the-art at the
time but had been superseded by newer, more efficient, or
more durable methods and materials.
-
- river
mile
- The same distance as a land mile, the river
mile is a measure of a point on any river relative to its
mouth, or its confluence with a larger body of water. Willamette
River Mile Zero is located at Kelly Point Park on the extreme
northwest corner of the city of Portland, where the Willamette
merges with the Columbia.
-
- suspension
bridge
- A bridge with which the roadway is supported
by main cables draped in parabolic curves from towers. The
roadway deck is connected to the main cables by suspenders,
and the main cable is secured to the ground by anchorages.
Expensive and long in construction, suspension bridges
are particularly rare in Oregon, with only three in the
state and only one (the Saint Johns) in the Willamette Valley.
-
- through
truss
- A bridge with the traffic roadway deck
located between the supporting trusses. Examples are the
Hawthorne, Steel, and Marquam.
-
- tied
arch
- An arch bridge designed like an
archer's bow, with the string ("tie", roadway)
connecting one end to the other. This compresses the arch
and tensions the tie. This is called for when it is not
feasible to support the arch horizontally at ground level.
the tie carries the horizontal load that would otherwise
be borne by the abutments. The Fremont is a tied-arch bridge.
-
- truss
- An arrangement of braced members, typically
a frame in which the basic structural unit is triangular.
Many of Portland's bridges are either complete trusses or
use trusses for stiffening members or supports.
-
- vertical-lift
bridge
- A movable bridge where the movable span
raises up and down, as an elevator. The Hawthorne, Steel,
and Interstate bridges are vertical-lift bridges.
-
- viaduct
- A bridge over land, usually with multiple
short or medium length spans. The Vista Avenue bridge over
SW Jefferson Street is a famous example of a viaduct. Other
well-known examples include the transition from the Grand/MLK
couplet to McLoughlin Blvd, and the eastern approaches to
the Morrison and Hawthorne bridges.
-
- Warren
truss
- A certain type of truss design, found in
the Marquam and Sellwood bridges. The distinguishing feature
of the Warren truss is a series of triangles with alternating
"A" and "V" shapes.
-
|
|
|
|
