Transcript Long-Term Monitoring of the IBS Bridge,

IBS Workshop at CAIT
14-15 June 2011, Rutgers University, NJ, USA
Long-term monitoring of US202NJ23 Bridge (Wayne, NJ)
Branko Glisic1, Daniele Inaudi2, Dorotea
Sigurdardottir1
1Princeton
University, Princeton, NJ, USA
2SMARTEC SA (Roctest Group), Switzerland
Outline
• Introduction
• Aims
• Monitoring system
• Installation
• Preliminary results
• Acknowledgements
Introduction
• SHM has potential to improve bridge safety and
management
• Although it is frequently applied to “signature”
structures, SHM can truly be declared as “useful” if its
utility is proven on “ordinary” (typical) structures
• Nevertheless, SHM is scarcely applied to typical
structures due to several reasons among which are
ease of use of data and the cost
• US202-NJ23 Bridge close to Wayne, NJ, is a good
example of typical structure and excellent opportunity
to test utility of SHM applied to typical structures
Aims of SHM
• To deploy affordable SHM system
• To register structural behavior of bridge girders over
long term and perform structural identification based
on periodic dynamic measurements
• To identify unusual behaviors related to monitored
parameters: average strain, average curvature, natural
frequency, and evaluate concrete-steel interaction
• To evaluate suitability of employed monitoring system
for achieving above aims in terms of measurement
performance and longevity
• To estimate value of information and evaluate longterm costs and benefits of monitoring
Fiber Bragg Grating (FBG) Sensors
• FBG = periodic refractive index perturbation generated in the core
• Strain and temperature in fiber change the back-reflected WL
~ 10 mm
l1(De1 ,DT1)
l1(De1 ,DT1)
l2(De2,DT2)
l2(De2 ,DT2)
The reflected wavelength depends
on the strain and temperature of
the fiber: l1=Ce·De+CT·DT+l1,0
Multiple FBG can be inscribed over the same fiber
Position of sensors
• Pairs of parallel sensors were installed in girders #2 and #5 of
the southbound part of the bridge
• Positions of the sensors were adjusted to the site conditions
Summary of instrumentation
• Reading unit:
– Dyn.: 250 Hz (1 kHz), 4 me, 1°C
– Static: 0.4 me, 0.1°C
– 12 (of 16) channels
• Girder #2:
– Gauge length at quarter span = 1m
– Gauge length at mid span = 2m
– 6 strain + 6 temperature sensors
• Girder #5:
– Gauge length at quarter span = 2m
– Gauge length at mid span = 2m
– 12 strain + 12 temperature sensors
Installation
• Using L-brackets, by gluing
Installation, continued
Examples of results
• Average strain generated by traffic has been
measured and several “events” were registered
• The following parameters will be calculated:
– average curvature
– position of center of gravity (concrete-steel
interaction)
– natural frequency
– thermal expansion
– correlation in behavior of two girders
• These parameters will be observed in long term
Examples of results
Acknowledgements
• Drexel University, in particular Prof. Emin Aktan, Prof.
Frank Moon, and graduate student Jeff Weidner for
opportunity to participate in the project, organization,
and help during the installation
• LTBP Program, NJDOT, and CAIT for opportunity to
participate in the project
• IBS partners for comprehension in sharing the lifts
during the installation
• Kevin for help in operating the lifts
• Yao Yao, graduate student of Princeton University for
availability and help in installation of sensors