Prefabricated Bridge Elements and Systems: A Winning Idea
For a growing number of State highway agencies, using prefabricated
structural elements and systems in bridge construction is the way to
go. While employing prefabricated elements isn't a new idea, these elements
are now being combined and used more extensively to facilitate bridge
construction in innovative ways. The technology is also getting a boost
from the American Association of State Highway and Transportation Officials'
Technology Implementation Group (TIG), which selected prefabricated
bridge elements and systems as one of its priority technologies last
year and is now moving forward with a Work Plan to promote the use of
prefabrication.
Prefabricated bridge elements, such as bent caps, can be manufactured
either on- or off-site, under controlled conditions, and brought to
the construction location ready for installation. Using prefabricated
elements and systems can increase construction zone safety, minimize
the traffic impacts of bridge construction projects, make construction
less disruptive for the environment, and improve constructibility. Safety
is improved and traffic impacts are lessened because some of the construction
is moved from the roadway to a remote site, minimizing the need for
lane closures, detours, and use of narrow lanes. Moving the construction
from the roadway can also lessen impacts on the surrounding environment.
Improved constructibility is achieved in situations where sophisticated
techniques would be needed to perform cast-in-place construction, such
as long water crossings or multi-level interchanges.
In recent years, the Virginia Department of Transportation (DOT) has
developed numerous projects suitable for the use of prefabricated bridge
systems. One of the most successful projects to date has been the James
River Bridge Restoration project, which began in June 2000. This project
involves the replacement of 13 bridges along the Interstate 95 corridor
in the Richmond area. The nearly 50-year-old bridges were found to be
suffering from structural deterioration, with the concrete and steel
surfaces needing to be replaced to maintain long-term safety. Starting
at 7 p.m., Monday through Thursday, the construction crew closes one-half
of the bridge to traffic, and removes two large sections of the bridge
surface. These sections are then replaced with new, prefabricated sections.
By 6 a.m. the following morning, the bridge is functioning and all travel
lanes are reopened. The project is scheduled to finish this year.
The Texas DOT, meanwhile, has found the use of prefabricated bent caps
to be extremely beneficial in bridge construction. For example, in 1994
Texas DOT improved constructibility and solved a traffic disruption
problem by using a prefabricated cap while working on a ramp for US
290. After the contract had been let and work started on the project,
it became clear that the formwork for the proposed cast-in-place cap
would interfere with traffic and require closing the ramp for an estimated
41 days. With Texas DOT's approval, the contractor instead precast the
straddle bent cap at the work site and lifted it into position. When
it was in place, workers post-tensioned bars and grouted the cap-to-column
connections. The ramp was closed to traffic for only 6 hours.
In 2000, Texas DOT began construction on a pair of conventional prestressed
concrete I-beam bridges over Lake Ray Hubbard near Dallas. To reduce
the amount of time workers would need to operate near power lines, the
contractor asked to precast the substructure bent caps as an alternative
to the original design of cast-in-place multi-column bents. The 102-span
bridge includes 43 precast bent caps, with precasting resulting in time
savings of 5-7 days per cap.
Ronnie Medlock of the Texas DOT says, "Although prefabricated
bridge elements such as beams and panels have been used for decades,
new elements and innovative ways to use them address pressing construction
needs, such as minimizing the impact of the work zone on traffic."
The TIG is working to build on these State successes and extend the
use of prefabricated elements and systems in bridge design and construction.
Some of the TIG activities underway include developing a brochure and
video and sending speakers to various national and regional conferences.
A prefabrication demonstration workshop will also be held this fall
in St. Louis, Missouri. For more information on the workshop, contact
Peter Clogston at the Federal Highway Administration, 573-638-2613 (fax:
573-636-9283; email: peter.clogston@fhwa.dot.gov).
For more information on prefabricated bridge elements and systems or
the activities of the TIG Implementation Panel on Prefabricated Bridge
Elements and Systems, contact Mary Lou Ralls at the Texas DOT, 512-416-2183
(email: mralls@dot.state.tx.us).
Information can also be found on the TIG Web site at www.aashtotig.org.
For more information on the I-95 James River Bridge Restoration project,
contact Dina Kukreja at Virginia DOT, 804-786-5172 (fax: 804-786-2988;
email: dina.kukreja@virginiadot.org).
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Articles in this issue:
Prefabricated Bridge Elements and Systems: A Winning Idea
Boosting Roadway Safety with Rumble Strips
Preserving the Future of Pennsylvania Bridges
Work Zone Research from A to Z
Design Guide Offers New Look at Mitigating Highway
Rockfall Hazards
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