Transportation Infrastructure
Florida Keys Hurricane 1935
Bridge Design
Dikes and water blocking causeways must not be built
for the purpose of transportation across estuaries.
Modern affordable bridge construction should be used for that,
e.g., low-cost long-span box girder bridges.
The most affordable box girder bridges have room
for two lanes of traffic, and space for pulling over.
These can be built of concrete,
in sections on shore with portable prestressing rigs,
and floated into position with a barge crane.
Newer methods allow transport of the bridge
segments over previously installed bridge segments
(instead of being floated out).
These affordable bridges can be high enough
to clear storm surges, with longer spans
to allow more laminar flow of water
beneath the bridge.
Figure 1:
Section of a prestressed concrete box girder bridge deck,
used in the Long Key bridge built in 1982,
with room for two lanes of traffic (one lane in each direction)
and room to pull over.
Each section was precast on shore in a
prestressing rig against previous section
for better installation fit.
This design was engineered to use longer
spans than was built, but the spans were shortened
at the request of state officials
to line up with the old viaduct (which should have
been removed instead).
Figure 2:
Example installation (not in the Florida Keys) of a
prestressed concrete box girder bridge section,
for multiple lanes of traffic in each direction,
showing how the sections fit together.
Figure 3:
Prestressed concrete box girder bridge,
built in 1985,
with one lane of traffic in each direction,
crossing Mjøsa (lake in Norway),
similar to the Long Key bridge but with longer spans
(
bridge info).
This type of bridge can be used in estuaries
to allow laminar water flow and storm water
flushing.
Figure 4:
Example of a concrete box girder bridge
with three lanes — two lanes
for vehicular traffic, the third lane
for pedestrians.
Ikema Island, Japan.
Note how the spans are much longer than
the dike bridges that traverse the entire Florida Keys,
in this case allowing water flow under the bridge.
[
Wiki]
Figure 5:
The example concrete box girder bridge of
the preceding figure, viewed from the bridge deck.
Pedestrian lane is on the right.
[
RaitaFuto]
Florida Keys Hurricane 1935
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