On-Line Bridge Monitoring: a Sound Based Sensor FusionTechnology for Preventing Failures
August 2007 - Princeton, NJ - Physical Acoustics Corporation (PAC), a member of MISTRAS Group
Inc., specializing in Nondestructive Testing (NDT) and Inspection, has developed digital wireless
sensor technology that assists Bridge Operators in preventing bridge failures. Rising demand for
ensuring the integrity and performance of our nation's aging bridges and infrastructure may
sometimes require more than typical visual inspection for evaluation of their structural conditions by
using advanced inspection technologies. The additional information from NDT can provide input to
authorities and assist in making informed and effective decisions with regards to planning for
maintenance, repair, rehabilitation or replacement. While there are several factors that can lead to
degradation and deterioration of a bridge, increased traffic on our nation's bridges, coupled with
corrosive environments, are the leading causes of deterioration for steel bridges. For concrete
bridges, corrosion of reinforcement due to chloride ingress, vehicle impact, concrete cracking and
fatigue are the major factors of degradation. On-line monitoring and sensor fusion can cover all
possible failure mechanisms including unpredictable deterioration.
Since 1972, PAC has applied sound technology, called Acoustic Emission (AE),
for "global" bridge monitoring while other sensors, such as vibration
accelerometers, strain gages, corrosion gages, etc., are used by our staff
and bridge engineers to assess the possible mechanism of failures and
predict bridge life. AE testing is a technique used to detect "warning
signals" forecasting defect formation and impeding failures in structural
materials. Cracks can be heard from remote distances by using AE sensors
similar to using geophones for earthquake detection and location or sonar
devices to detect enemy submarines. Commonly used visual inspection to detect small
cracks/defects, is like finding a needle in a haystack and impossible in areas that are inaccessible or
hard to access.
Per the NY Times, "warning sounds were heard for months by neighbors prior to
the I-95 CT bridge collapse 15 years ago" reports Dr. Sotirios J. Vahaviolos,
Founder and Chairman/CEO of PAC and MISTRAS Group Inc. The airport
manager at Charles De Gaulle airport reported to CNN that they also heard
warning sounds a couple of years prior to the collapse of a terminal. In both
these instances, PAC's systems could have differentiated "crack sounds" from
other normal daily sounds in a bridge structure including heavy rain.
Since the early 1990's bridge monitoring using AE has been investigated by the
Federal Highway Administration (FHWA) that continues to fund development,
testing and demonstrations on the use of AE for bridge inspection and
monitoring. PAC has been awarded several FHWA contracts since the late
1980's and has successfully monitored over 20 bridges. "It is only because of State DOT's and
government funding that has prevented wide scale deployment of on-line monitoring using sensor
fusion and wireless technologies on bridges" states Dr. Vahaviolos. More recently, FHWA selectedPAC's Sensor Highway II(TM) System for awarding and participation under the Steel Bridge Testing
Program.
"AE can also be used by Homeland Security for prevention of vandalism" states PAC's National Sales
& Applications Director, Terry Tamutus. Recently youths with hacksaws cut dozens of wires from
four main cables on a cable stay bridge. "It caused more than $2MM in repairs and a possible
catastrophic bridge failure. An on-line AE system could have easily detected the start of a cable
cutting and could have alerted authorities through wireless or internet based communication
technology" states Tamutus.
"We have the technology for Bridge Health Monitoring now and are ready to team up with Bridge
Operators in order to prevent catastrophic failures from naturally occurring structural flaws that are
the result of an aging infrastructure" concludes Dr. Vahaviolos.
MISTRAS Group Inc. provides Nondestructive testing products and services under the well known
brand names of CONAM Inspection and Engineering Services Inc., Physical Acoustics Corporation,
Code Services, Quality Services Laboratories Inc., Caliber Inspection, PRI, NDT Automation, and
Vibra-Metrics. MISTRAS Group provides Mechanical Asset Inspection and Integrity Solutions to the
Energy, Aerospace, Manufacturing and Gas & Oil Sectors as well as strategic on-line instrumentation
that facilitates Plant Asset Management decisions. In addition, MISTRAS is the leading provider of
Enterprise Solution Software that aids in the safe and profitable operation of industrial facilities
worldwide.
For more information, please visit the company's website at www.mistrasgroup.com or contact the
main office at 609-716-4000.
