Scanning Tour Showcases a Prefabricated Future
From whole bridges that can be completely built off site and moved
into place to full-depth prefabricated concrete bridge decks, participants
in a recent international scanning tour got a glimpse of a future that
not only looks prefabricated, but delivers projects at significantly
accelerated speed.
The Federal Highway Administration (FHWA) and the American Association
of State Highway and Transportation Officials (AASHTO) sponsored the
international scanning tour in April 2004 to learn more about prefabricated
bridge technologies being used in Europe and Japan, including design
methodologies, construction techniques, and maintenance and inspection
processes. The scanning team visited Japan, the Netherlands, Belgium,
Germany, and France. Team members represented FHWA, State and county
highway agencies, industry, and academia.
The primary focus of the tour was on bridges with span lengths ranging
from 6 to 40 m (20 to 140 ft), which represents the bulk of structures
in the United States. Depending on the specific site conditions, the
use of prefabricated bridge technologies has proven in Japan and Europe
that it can minimize traffic disruptions, improve constructibility,
increase quality, frequently reduce initial cost, lower life-cycle costs,
and minimize disruptions to the environment.
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| A 3600 ton, two-span bridge is moved in Amsterdam using
an SPMT. Bottom: An SPMT in Belgium. |
After completing the tour, the team identified 10 technologies that
it recommended for possible implementation in the United States. The
most compelling technology the team observed was the use of vehicles
known as self-propelled modular transporters (SPMTs) to move large bridge
components or complete bridges built off site and then place them into
position quickly for use. "The ability to build complete bridges off
site and then move them into place was what struck us the most," says
team member Henry Russell of Henry G. Russell, Inc. The multi-axle,
computer controlled vehicles can move in any horizontal direction, while
maintaining their payload geometry and keeping equal axle loads. In
the Netherlands, for example, a two-span bridge weighing 3600 tons was
moved 120 m (393 ft) in 2 hours.
"The use of SPMTs could be the biggest change in many, many years for
bridge building," says team cochair Mary Lou Ralls of the Texas Department
of Transportation (TxDOT). Texas plans to begin work on bridge projects
in 2005 that will use the technology on the I-35 corridor in its Waco
District. "The bridges will be constructed next to the site and then
moved on to the site using SPMTs. For a bridge project that we're currently
designing, only one direction of I-35 mainlane traffic will have to
be detoured to a frontage road, and this detour will only be required
for one night," says Ralls.
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| These photos show France's Poutre Dalle system, which
eliminates the need to place and remove temporary formwork for bridge
decks during construction. |
Other observed methods of more rapidly moving bridge components include:
- Horizontally skidding or sliding bridges into place.
- Incrementally launching bridges over valleys or above existing highways.
- Floating bridges into place using barges or by building a temporary
dry dock.
- Building bridges alongside an existing roadway and then rotating
them into place.
- Vertically lifting bridges.
Additional recommended technologies observed by the team include systems
that eliminate the need to place and remove temporary formwork for bridge
decks during construction. In Germany, partial depth concrete decks
are cast on steel or concrete beams prior to erection of the beams.
After the beams are erected, the edges of each deck unit abut the adjacent
member, eliminating the need to place additional formwork for the cast-in-place
concrete. This process accelerates construction and increases safety,
as a safe working surface is available immediately after beam erection.
France's Poutre Dalle system also eliminates the need for formwork.
In this system, inverted T-beams are placed adjacent to each other and
then made composite with cast-in-place concrete placed between the webs
of the tees and over the tops of the stems to form a solid member. "This
technology presents particularly good opportunities for implementation
with smaller bridges," notes team member Dan Dorgan of the Minnesota
Department of Transportation. Minnesota is looking at using the technology
for two upcoming bridge projects. "The advantages of using the technology
include faster construction and less disturbance to the surrounding
site," says Dorgan.
The use of full-depth prefabricated concrete bridge deck panels was
also observed. The deck panels are made composite through the use of
steel studs located in grout-filled pockets in the concrete deck slabs.
Employing these prefabricated concrete decks reduces construction time
by eliminating the need to erect formwork and use cast-in-place concrete.
"Using the technology would be particularly timely here in the United
States because of the nationwide push for accelerated construction,"
says team member Shri Bhidé of the Portland Cement Association.
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| A partial deck concrete deck is cast on steel
beams on German Federal Autobahn Route 8A East between Munich, Germany,
and Salzburg, Austria. |
The team will be issuing an implementation plan this fall containing
recommendations for introducing the observed technologies to highway
agencies and others, using such means as demonstration projects, showcases,
and workshops. The team will also be releasing a report on the scanning
tour. A preliminary summary report is available online now at www.fhwa.dot.gov/bridge/prefab/pbesscan.htm.
For more information about the scanning tour, contact Benjamin Tang
at FHWA, 202-366-4592 (email: benjamin.tang@fhwa.dot.gov).
For More Information
To learn more about prefabricated bridge elements and systems, visit
www.fhwa.dot.gov/bridge/prefab.
The Web site highlights the advantages of prefabrication and presents
details on how prefabricated bridge elements and systems have been used
around the country. Also featured are information on best practices
and video clips of numerous bridge projects.
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