[Editors] MIT: New device "sees" bridge damage

[Elizabeth Thomson]

MIT News Office
Massachusetts Institute of Technology
Room 11-400
77 Massachusetts Avenue
Cambridge, MA  02139-4307
Phone: 617-253-2700
http://web.mit.edu/newsoffice/www

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Handheld device 'sees' damage in concrete bridges, piers

Aging structures can be inspected immediately, onsite
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For Immediate Release
WEDNESDAY, MAY 23, 2007
Contact: Elizabeth A. Thomson, MIT News Office
Phone: 617-258-5402
Email: thomson at mit.edu

PHOTO , IMAGE AVAILABLE

CAMBRIDGE, Mass.--Engineers at MIT have developed a new technique for 
detecting damage in concrete bridges and piers that could increase 
the safety of aging infrastructure by allowing easier, more frequent, 
onsite inspections that don't interfere with traffic or service.

The technique involves use of a hand-held radar device that can "see" 
through the fiberglass-polymer wrapping often used to strengthen 
aging concrete columns to detect damage behind the wrapping not 
visible to the naked eye. Such damage can occur on the concrete 
itself, or to areas where layers of the wrapping have come loose from 
one another or even debonded from the concrete.

The new noninvasive technique can be used onsite from a distance of 
more than 10 meters (30 feet) and requires no dismantling or 
obstruction of the infrastructure. It provides immediate, onsite 
feedback.

Called FAR-NDT (far-field airborne radar nondestructive testing), the 
technique could prove especially advantageous for bridges that span 
rivers or highways, which can prove inaccessible for other inspection 
techniques. The MIT researchers first reported the technique in the 
Proceedings of the International Conference on Structural Faults and 
Repair held in Edinburgh, Scotland, last year.

"The use of radar for detecting hidden defects and deterioration 
behind covered surfaces offers great potential for wide-range use in 
assessing the safety of bridges and buildings that have been 
retrofitted with composite materials," said Professor Oral 
Buyukozturk of the Department of Civil and Environmental Engineering 
(CEE), who developed the technique with CEE graduate student Tzu-Yang 
Yu and Dennis Blejer of MIT Lincoln Laboratory, where prototype radar 
measurements were made.

Fiberglass-polymer jacketing--shiny, textured fabric in black or 
ivory often seen wrapped around concrete columns--is widely used to 
upgrade existing concrete structures so they can carry a greater load 
or sustain additional earthquake impact. The wrap is also commonly 
used to retrofit structures that are damaged or deteriorating from 
weather or other wear.

Techniques presently available for inspecting these 
fiberglass-polymer jacketing systems require the inspector to come in 
direct or close contact with the structure. Some actually require 
removal of a physical sample, which itself could create a safety 
issue. The advantage of the new technique is that it allows a rapid 
inspection from a distance and provides computerized visualization of 
the internal damages.

"This technique would allow the engineers to perform reliable, 
in-situ inspection for visualizing and characterizing hidden damages 
from distances without having to endanger the structure by taking 
specimens from it, and at the same time, without disturbing the 
traffic or service," said Yu, whose Ph.D. thesis will focus on this 
research. "The project is an excellent example of bridging 
fundamental science and engineering applications."

The researchers have demonstrated the validity and potential of the 
new technique through experiments and computer simulations by sending 
and receiving radar signals using a "horn" antenna to inspect bridge 
piers from distances of more than 10 meters. In their experiments, a 
horn antenna transmits a radar signal to a fiber-wrapped concrete 
specimen, which reflects the signal back to the antenna. The 
collected data are then converted by an imaging algorithm into a 
visualization of the interior of the specimen, including any damage.

The researchers say that the concept has been validated by their 
initial experimental results using an existing prototype radar system 
and by computer simulations. Future development of appropriate 
portable radar equipment for onsite use is necessary before the 
system can be placed in widespread use by industry.

The work is funded by the National Science Foundation.

Written by Denise Brehm, Civil and Environmental Engineering