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Media
Contacts:
Dr. Amir Mirmiran,
919/513-1735
Linda E. Rudd,
Engineering Publications, 919/515-3848
Feb.
10, 2003
NC State
Engineer "Guides" New Polymer Bridge-Repair
Technique
FOR
IMMEDIATE RELEASE
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How
many times have you stopped your car on a bridge
and felt the bridge shake and rumble beneath you
as other cars pass over? Questions about the bridge's
integrity pop into your head, but you usually
just continue on your way when the light changes.
For
North Carolina State University researcher and
professor of civil engineering Dr. Amir Mirmiran,
questions about the integrity of bridges are more
than passing thoughts. Part of his work addresses
bridge stabilization and repair, and one current
project for the National Academy of Sciences involves
development of new construction specifications
and a process-control manual for use by the American
Association of State Highway and Transportation
Officials (AASHTO) Subcommittee on Bridges and
Structures.
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The
underside of a bridge in Florida shows damage
from vehicles that exceeded the height limit.
(All photos by Dr. Mohsen Shahawy.)
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AASHTO
strives to make bridges safer by developing design guidelines
and procedure manuals for all U.S. state departments
of transportation. Recent development of new materials
that could be used to reinforce bridges has sparked
interest in the safe application of this technological
advance to existing structures. One new material, fiber-reinforced
polymer (FRP), is the subject of Mirmiran's research
project.
FRP
is a very strong, flexible fabric made of carbon or
glass. With a resin such as epoxy, FRP can be bonded
to a concrete surface to expedite bridge repair, in
many cases without even closing the bridge to traffic
during the process. Applying FRP is not labor-intensive
compared with traditional methods, and heavy equipment
generally is not required. Strengthening and repairing
a bridge is much faster and more economical using this
new material. Existing bridges can even be upgraded
to accommodate heavier, wider vehicles.
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Workers
apply fiber-reinforced polymer to the damaged
bridge.
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The
research project, led by Mirmiran, involves
a collaboration among NC State, the SDR Engineering
Consultants, the University of Missouri-Rolla
and the University of California-San Diego.
To assuage worries of the departments of transportation
that FRP materials used for repairs may not
be applied properly, Mirmiran's group is creating
a field guide and manual for the application
of FRP in the repair and retrofit of bridges.
The manual is in the revision stage; Mirmiran
hopes a final version will be ready to submit
to the National Academy of Sciences this summer.
According
to Mirmiran, "Eventually the manual will
be a document that every bridge engineer in
every state will use."According to Mirmiran,
"Eventually the manual will be a document
that every bridge engineer in every state will
use."
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Once
the document is adopted by state departments of transportation,
Mirmiran's research group wants to develop a series
of workshops for each state. "The next phase of
our work will be training state transportation engineers,"
said Mirmiran. During a two-day traveling workshop,
facilitators would outline the FRP application process
and teach highway workers how to use the field guide
and an inspection manual.
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Another
aspect of the project is nondestructive testing
and evaluation of the repairs, which will be incorporated
into the inspection manual. "One of the purposes
of this project is not only to demonstrate the
placement of this material but also to show how
the material can be inspected right after the
reconstruction to make sure that it has bonded
properly," said Mirmiran. Nondestructive
evaluation methods include both low-tech methods,
such as visual and acoustic tests (tapping on
the bridge), and sophisticated (thermographic
and ultrasonic) alternatives. Based on these evaluation
methods, Mirmiran has developed acceptance criteria
so departments of transportation will know if
a repaired bridge is safe.
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The
completed repair makes the bridge safe again.
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Bridge
safety - the ultimate goal of Mirmiran's work - will
be improved once these very practical documents are
finished and distributed.
-rudd-
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Raleigh,
NC 27695
