BRIDGE ENGINEERING ASSOCIATION
2005 NEW YORK CITY BRIDGE CONFERENCE
SEPTEMBER 12-13, 2005
Dynamic and Static Displacement Monitoring with Noncontacting Interferometric Radar System
NJ Route 23 Bridge - Structure No. 1618-150
Over US 202, Ramps M & N and Norfolk Southern Railroad
Wayne Township near Passaic, New Jersey
Eugenia K. Roman, P.E.
Vice President
Olson Engineering, Inc.
New Jersey - Colorado - New Mexico
BRIDGE ENGINEERING ASSOCIATION
2005 NEW YORK CITY BRIDGE CONFERENCE
SEPTEMBER 12-13, 2005
IBIS-S System Principle Description
The IBIS-S system is a Stepped-Frequency Continuous Wave (SF-CW) coherent radar
with Interferometric capabilities, dedicated to remote monitoring of static or dynamic
displacements of civil structures.
Displacement is measured by
comparing phase information from the
reflected airborne radar waves, which
are collected at time intervals.
TX
RX
1
TX
RX
2
d
BRIDGE ENGINEERING ASSOCIATION
IBIS-S System Principle Description
•IBIS-S
Radar system is a 1-D
measurement tool, measuring
displacement in the line of
sight of the radar unit
•Separate
targets at the same
distance from the radar are
averaged into a single
reflection echo
•The separation between
targets must be at least 2.5 ft
(0.75 m)
• AKA called the range
bin size
•The
shape of the transmitted
radar beam can be
manipulated with different
horn attachments to focus on
targets of interest.
2005 NEW YORK CITY BRIDGE CONFERENCE
SEPTEMBER 12-13, 2005
BRIDGE ENGINEERING ASSOCIATION
2005 NEW YORK CITY BRIDGE CONFERENCE
SEPTEMBER 12-13, 2005
IBIS-S System Principle Description
The IBIS-S measures displacement in the direction of the line of sight of the
system. Knowledge of the acquisition geometry is used to calculate the real vertical
displacement.
The calculation necessarily assumes that the horizontal displacement is zero.
R
h
dp
α
d 
dp
sin(  )
d
sin(  ) 
h
R
d  dp 
R
h
The distance R
is measured by
IBIS-S
BRIDGE ENGINEERING ASSOCIATION
2005 NEW YORK CITY BRIDGE CONFERENCE
SEPTEMBER 12-13, 2005
IBIS-S Set-up
•IBIS-S
positioned directly under
the centerline of Pier 1W looking
North at Span 2
BRIDGE ENGINEERING ASSOCIATION
IBIS-S Set-up
•Three
corner reflectors were installed
on girder 2W3 in order to:
•
create more distinguishable
reflection points along the
structure
•
to provide direct comparison
data with installed string
potentiometers
2005 NEW YORK CITY BRIDGE CONFERENCE
SEPTEMBER 12-13, 2005
BRIDGE ENGINEERING ASSOCIATION
IBIS-S Radar Reflection Amplitudes
2005 NEW YORK CITY BRIDGE CONFERENCE
SEPTEMBER 12-13, 2005
BRIDGE ENGINEERING ASSOCIATION
2005 NEW YORK CITY BRIDGE CONFERENCE
SEPTEMBER 12-13, 2005
IBIS-S Dynamic Results of Ambient Traffic Data
•Example
time domain displacement
vibration data due to typical traffic
loading.
•An
FFT was applied to ambient
vibration data in order to determine the
resonant frequency of the structure.
•The
bridge span had an apparent
resonant frequency of 2.76 Hz.
•In
more extensive studies modal
shapes can also be determined.
BRIDGE ENGINEERING ASSOCIATION
2005 NEW YORK CITY BRIDGE CONFERENCE
SEPTEMBER 12-13, 2005
IBIS-S Static Load Test Results
0.58” (14.69 mm)
0.58” (14.84 mm)
0.85” (21.76 mm)
Load Tests results of the three corner reflectors with loads at ~ ¾,
½, and ¼ Spans, six loaded trucks, load test duration ~ 1 hr
BRIDGE ENGINEERING ASSOCIATION
2005 NEW YORK CITY BRIDGE CONFERENCE
SEPTEMBER 12-13, 2005
IBIS-S Test Result Conclusions
•The
system can be installed very quickly and easily
•Accurate to
0.0004 inch (1/100 mm)
•The
system is simple to use and the resulting data is easy to analyze and
easily understood due to the actual measurement of displacement.
•The
system can provide access to otherwise difficult structures.
•The
system is extremely accurate and can provide both dynamic and static
displacements.
•Overall, the
system is ideally suited for rapid load testing of bridges with
minimal interference due to access and incredible potential of the quantity,
quality, and accuracy of measured data.