Figure
27: Evans Crary Bridge
construction, Florida
Figure
28: Evans Crary Bridge
construction, Florida
A
balanced cantilever
design was revised to a
span-by-span segmental
design with near-record
spans of 180 feet for
the Evans Crary Bridge
crossing Florida's St.
Lucie River by PCL Civil
Constructors and Finley
McNary Engineers.
The redesign resulted in
savings of $770,000.00
for the Florida
Department of
Transportation and
facilitated construction
in the following ways:
•PCL wanted to
access the bridge by
water only, and using
span-by-span rather than
the balanced cantilever
method allowed them to
do that.
•Because all
transportation of the
precast segments could
be done by water, PCL
was able to build larger
segmentsă15 feet
instead of 10. That
meant that one casting
machine could be
eliminated, saving
significant time and
money. Transporting by
water also reduced the
headaches and cost of
moving the oversized
precast segments by
roadway.
•Longer segments
provided faster
construction and reduced
the amount of material,
equipment, and labor
required.
The bridge's twin,
precast segmental
structures are 15.044
meters wide, 909 meters
long, and are separated
by a 450-mm gap. Rising
at a vertical grade of
5.2%, the bridge
provides a 19.885-meter
vertical and
27.440-meter horizontal
clearance over the St.
Lucie River. It is
continuous from end to
end with no intermediate
expansion joints. The
box girder is a constant
2.45 meters deep. The
center foundations were
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designed
for a 9,700 KN ship
impact load, using a
common footing for
both structures where
the ship impact load
is applied. The piers
are cast-in-place with
a flared top.
Construction views are
presented in Figures
27 and 28.
Three main
restrictions for the
bridge's redesign
were:
Box girder section.
One of the
restrictions for the
redesign was that the
aesthetics could not
be changed. Therefore,
the construction team
did not revise the
exterior dimensions of
the cross-section. The
original design used
varying web thickness
and a varying bottom
slab thickness. The
team selected a
constant cross-section
for the span-by-span
redesign. Then, they
reduced the web
thickness since draped
tendons that would
reduce the shear force
carried by the webs
would be used with the
span-by-span
construction. Since
the cantilever tendons
anchoring in the top
slab were eliminated,
the thickness of the
interior haunches was
also reduced.
Post-tensioning.
The original design
was based on straight
cantilever tendons and
continuity tendons.
The redesign used
draped external
tendons that extended
the full span length
and were internal to
the bottom slab in
between deviation
points. It also used
straight internal
tendons in the top and
bottom slab that
extended the full span
length and internal
tendons in the bottom
slab anchored in
blisters. There was
over a 50% reduction
in the number of
tendons and a 40%
reduction in the
weight of longitudinal
prestressing. The team
also relocated the
temporary PT bars used
to compress the epoxy
from internal to the
top and bottom slabs
to external so that
they could be reused.
Segments.
With the handling of
the segments being
accomplished entirely
with barge-mounted
equipment, segment
weights up to 95 tons
could be used. The
original design used
split pier segments.
The pier segments were
redesigned as a single
piece that weighed 95
tons. The typical
segment length was
increased from 3.2
meters to 4.72 meters
so that they also
weighed 95 tons.
Because of the 35%
reduction in the
number of precast
segments
(approximately 200
segments eliminated),
PCL was able to use
only one typical
casting machine.
The casting yard is
located in Stuart,
Florida, about 20
miles from the project
site. Segments were
barged to the project
site. The pier segment
machine will be
converted to cast the
four expansion joint
segments after the
pier segments are
cast. Segments are
match-cast using the
shortline method of
casting and
transversely
post-tensioned.
On July 14, 1999,
at a ceremony in
Branson, Missouri, the
Florida DOT received
AASHTO's award for
Most Innovative
Proposal During
Construction for the
Evans Crary Bridge.
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