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Eugenia K. Roman, P.E. Vice President Olson Engineering, Inc. New Jersey - Colorado - New Mexico

Dynamic and Static Displacement Monitoring with Non-contacting 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.

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Eugenia K. Roman, P.E. Vice President Olson Engineering, Inc. New Jersey - Colorado - New Mexico

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  1. Dynamic and Static Displacement Monitoring with Non-contacting Interferometric Radar SystemNJ Route 23 Bridge - Structure No. 1618-150Over US 202, Ramps M & N and Norfolk Southern RailroadWayne Township near Passaic, New Jersey Eugenia K. Roman, P.E. Vice President Olson Engineering, Inc. New Jersey - Colorado - New Mexico

  2. 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 TX RX RX d d TX TX RX RX

  3. 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.

  4. R dp h α d 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. The distance R is measured by IBIS-S

  5. IBIS-S Set-up • IBIS-S positioned directly under the centerline of Pier 1W looking North at Span 2

  6. 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

  7. IBIS-S Radar Reflection Amplitudes

  8. 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.

  9. Load Tests results of the three corner reflectors with loads at ~ ¾, ½, and ¼ Spans, six loaded trucks, load test duration ~ 1 hr IBIS-S Static Load Test Results 0.58” (14.69 mm) 0.58” (14.84 mm) 0.85” (21.76 mm)

  10. 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.

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