ibis-s brochure olson bridges r3 web

8/12/2019 Ibis-s Brochure Olson Bridges r3 Web

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Olson Engineering worked in close cooperation with the University

of Minnesota to demonstrate the IBIS-S technology on the Minnesota

DOTs St. Anthony Falls Bridge on I-35W in Minneapolis, Minnesota.

Comparisons will be made in the near future of controlled load test

results between the many embedded sensors in this bridge and

the IBIS-S displacement measurements of the southbound bridge.

(in the foreground above).

Olson Engineering provided a demonstration of the IBIS-S on a

girder of a bridge in northern New Jersey that is being studied

as part of the FHWAs Long Term Bridge Performance Monitoring

project which is being conducted by Rutgers University and

Parsons Brinckerhoff. The results of controlled load tests by Drexel

University with string potentiometer displacement measurements

and the IBIS-S displacement measurements of the bridge girder will

be compared in the near future as part of this research.

FHWAs Long Term Bridge Performance Monitoring Project

St. Anthony Falls Bridge, Minneapolis, Minnesota

Recent Olson Engineering IBIS-S Projects


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IBIS-S is an innovative microwave radar sensor,

developed by IDS Georadar of Pisa, Italy in collaboration

with the Department of Electronics and Telecommunications

of Florence University. It is able to simultaneously measure

the displacement response of multiple points belonging to

a structure with an accuracy on the order of a hundredthof a millimeter (0.0004 inch). Vibration frequencies can be

measured from 0 up to a maximum of 100 Hz.

IBIS-S can be used to remotely measure structural static

deflections as well as vibration displacements to identify

resonant frequencies and mode shapes. In addition to its non-

contact feature, the new displacement vibration measuring

system provides other advantages including quick set-up time

and a wide frequency range of response and portability.

Throughout this brochure, Olson is highlighting various case histories on IBIS-S projects performedby IDS exclusively, by Olson Engineering exclusively, and those projects performed jointly for various

demonstrations within the USA. Geotechnical engineers may also be interested in the IBIS-L for landslide/

slope stability monitoring. Visit our website at www.OlsonInstruments.com to learn more about our

infrastructure instruments for structural health monitoring (SHM), nondestructive evaluation (NDE)

and seismic geophyical instruments for sale, or visit www.OlsonEngineering.com which specializes in

Imaging the Infrastructure for Assessment, Monitoring & Repair. Training is available by one of our

Olson Engineering specialists. Olson is celebrating over 26 years in business and would like to be your

bridge infrastructure specialist for any project, now or in the future. We are located in Wheat Ridge,

Colorado USA a suburb NW of downtown Denver, CO.

If you are interested in purchasing an IBIS-S System or any of our other instruments, contact:

email: [email protected]

website: www.OlsonInstruments.com

phone: 303.423.1212

If you are interested in Olsons Professional Consulting Services, contact:


website: www.OlsonEngineering.com

phone: 303.423.1212

Table of Contents IBIS-S Case HistoriesImaging by Interferometric Survey IBIS-S


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IBIS-S Components

The IBIS-S system is based on interferometric and wide band

waveform principles. It is composed of a sensor module, a controlPC and a 12 volt power supply unit. The sensor module [A] is a

coherent radar unit, generating, transmitting and receiving the

electromagnetic signals to be processed in order to compute the

displacement time-histories of measurement points. The system

has a maximum operational distance (for minimum 40Hz vibration

sampling frequency) of 500 m (1640 ft), a maximum sampling

frequency of 200 Hz, (permits measuring vibration frequencies up

to 100 Hz) and a displacement sensitivity of up to 0.01 mm (0.0004

in). It can measure static displacements up to a distance of 1000m

(3280 ft). The IBIS-S system is extremely portable with the entire

system weighing less than 100 lbs. The system can easily be rapidly

deployed and can be operated in all weather conditions.

The sensor module, including two airhorn antennas [A] fortransmission and reception of the 17.1 MHz electromagnetic

waves, exhibit a typical super heterodyne architecture. The base-

band section consists of a Direct Digital Synthesis (DDS) device to

obtain fast frequency hopping. A tuneable sine wave is generated

through a high-speed D/A converter, reading a sine lookup table in

response to digital tuning and a precision clock source. The radio-

frequency section radiates at a center frequency of 17.2 GHz wi

a maximum bandwidth of 200 MHz; hence, the radar is classifieas Ku-band, according to the standard radar-frequency letter-ban

nomenclature from IEEE Standard 521-1984. The system was ful

approved for use at any site across the USA and its territories i

February, 2011 with the operator of the system only requiring

general FCC license for its use. A final calibration section in th

module provides the necessary phase stability. Design specification

on phase uncertainty are suitable for measuring short-term

displacements with a range uncer tainty lower than 0.01 mm (0.000

in) and an intrinsic accuracy of 0.001 mm (0.00004 inches). Th

sensor module is installed on a tripod equipped with a rotating hea

[C], allowing the sensor to be orientated in the desired directio

The module has a USB interface for connection with the control P

[B]and an interface for the power supply module.

The control PC (Panasonic Toughbook CF-19) includes the softwa

for system management and is used to configure the acquisitio

parameters, store the acquired signals, process the data and vie

the initial results in real time. The system can be powered by an

12 volt battery.

INTRODUCTION

Imaging by Interferometric Survey [IBIS-S] Basic Description

[A] Sensor Unit:

Signal Transmitter and Receiver

Viewfinder

Airhorn Antenna

- Additional antennas for narrow to wideviews and vertical to horizontal

[B] Processing Unit :

Control PC with Management Software

Parameter Setting:

- Signal Generator

- Signal Acquisition

First Result Rendering

[C] Tripod and 3-D Rotating Head

[D] Power Supply Unit (not shown)

[A]

[B ] [C ]

Airhorn Antenna


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Imaging by Interferometric Survey [IBIS-S] Basic Description 3

INTRODUCTION

Figure 3.Range bin resolution concept diagram, 0.75 m per bin.

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When a target surface moves with respect to the sensor module

(emitting and back-receiving the electromagnetic wave), a phase

shift arises between the signals reflected by the target surface at

different times. Hence, the displacement of the investigated object

is determined from the phase shift measured by the radar sensor at

the different discrete acquisition times. The radial displacement dp

(i.e. the displacement along the direction of wave propagation) and

the phase shift are linked by the following:

(5)

where is the wavelength of the electromagnetic wave radar signal.

Monitoring Applications of the IBIS-S Radar System

Static Monitoring: Dynamic Monitoring:

Structural Load Testing Structural resonance frequency measurement

Structural displacement and collapse hazards Structural modal shape analysis

Cultural heritage preservation Real time monitoring of deformation

Advantages over Traditional Methods

Radar for interferometric imaging of bridge displacements in load tests up to an accuracy of0.0004" with modal vibration measurements and analysis (0 to 100 Hz)

Real-time simultaneous mapping of deformations

Fast installation and operation

Stactic and dynamic monitoring

Structural vibration sampling up to 100 Hz

Autonomous operation; 24/7 in all weather conditions!

Provides direct line of sight displacements, not derived quantities, in one dimension


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Table of Contents IBIS-S Case Histories

Type of Structure: Test for: Page

A.Bridges

A1. Olginate Cable-stayed Bridge [Italy] Vibration Monitoring of Stay Cables for Tension Force Balancing 8-9

A2. Bordolano Cable-stayed Bridge [Italy] Dynamic Measurements on the Forestays of a Cable-stayed Bridge 10-11

A3. Highway Flyover Bridge, CO [USA] Static Displacement and Dynamic Vibration Monitoring of a Concrete Bridge 12-13

A4. Manhattan Bridge, NY [USA] Static Displacement and Dynamic Vibration Monitoring of a Steel Bridge 14-15

A5. Capriate Bridge [Italy] Ambient Vibration Testing for Modal Analysis 16-17

A6. Kuranda Scenic Railway Bridge [AU] Dynamic Monitoring of Vertical Displacements Caused by a Train 18-19

Flag Legend: Case Histories performed by IDS Georadar, Pisa, Italy

Case Histories performed by Olson Engineering, Inc. [USA] and IDS Georadar


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CASE HISTORY

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Figure 2.IBIS-S position in the survey for thedownstream surveys.

Testing Procedure

Figure 1.(a) Elevation and typical cross-sections of the bridge (dimensions in m).(b) First array; testing on the downstream side.

Vibration Monitoring of Stay Cables for Tension Force Balancing

Project: Cesare Cant cable-stayed roadway bridge

Project Location:Roadway bridge crossing the Adda River, Italy

Bridge Construction:Pre-stressed concrete deck, formed by a centralspan of 110 m and two lateral spans of 55 m. The deck is suspended from 24

pairs of cable-stays, arranged in a semi-fan and connected to two H-shaped

reinforced concrete towers, reaching the height of approximately 38 m above

the foundation. Elevation and plan views are shown in Figure 1.

Project Scope:The measurement of vibrations on one array of stay-cables was performed by simultaneously using conventional piezoelectric

accelerometers and the IBIS-S radar sensor, in order to demonstrate the

effectiveness of microwave remote sensing and its accuracy in terms of

both natural frequencies and cable tension forces.

After the main phase of cable tensioning, vibration measurements

were carried out on all cables of the bridge by using conventionalaccelorometers (WR, model 731A) to check the tension forces. In

addition, the global dynamic characteristics of the bridge were

determined by ambient vibration testing (AVT), in order to optimize

the subsequent phase of adjustment of cable forces. Prior to opening

the bridge to traffic, more extensive AVT of the deck and towers

were carried out as part of the bridge reception tests. Next, dynamic

measurements on two arrays of cables were carried out by

simultaneously using piezoelectric accelerometers and the IBIS-S

radar system in order to verify the reliability and accuracy of the

radar technique.

During the tests, the ambient excitation was mainly provided by t

2-axle trucks with 340 kN gross weight each, crossing the bridwith symmetric and eccentric passages and speeds in the range

10-40 km/hr. In the test of the first array, cables S '07

- S'12

(Fig.1

the IBIS-S was placed at the base of the tower on the Calolzioco

side (Fig.2) and inclined at 55 upward; accelerometer and ra

data were acquired simultaneously at a rate of 200 Hz over a per

of 1700 s. The range profile of the test scenario is presented in Fig

it is observed that after some close and neighboring peaks around

range of 10 m, corresponding to the concrete transverse be

providing the anchorage for cable S'07,

f ive well-defined peaks clea

identify the positions of cables S'08

- S'12

.

Aerial view of the Cesare Cant cable-stayed bridge

Array 1

Down

stream

Array

1

a

b

A1


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A1

Figure 3.Range prole of the test scenario.

Vibration Monitoring of Stay Cables for Tension Force Balancing

The analysis of the results obtained by the radar sensor first included

the qualitative inspection of the deflection measurements. Figure 4a

shows an example of displacement time-history measured on the

investigated stay-cable S'12

; it should be noted that, as it has to be

expected for a stay-cable, the fundamental period is clearly detected

in the displacement signal. Although radar and conventional

measurements refer to different points of the cable (Fig. 1b), the

comparison between the time-histories simultaneously recorded by

the two measurement systems provides valuable information. An

example comparison is given in Figure 4b, where the acceleration

computed by twice differentiating the displacement obtained from

the radar is compared to the one simultaneously recorded by the

accelerometer. It can be observed that the two time series, which

refer to two different points almost symmetrically placed with

respect to the midpoint of the stay-cable, exhibit the same time

evolution and very similar amplitudes. To fur ther enhance this point,

Figure 4b is superimposed over Figure 4a, showing the near perfect

similarity between the IBIS-S and the accelerometer data.

Although the ASDs of Figure 5 are associated with different mechanical

quantities measured (displacement and acceleration) and to

different points of the stay cable, the spectral plots clearly

highlight an excellent agreement in terms of local natural

frequencies of the cable, marked with the vertical dashed lines,

and are characterized by equally spaced and well-defined peaks

in the investigated frequency range. Global natural frequencies

of the bridge-identified in the bridge dynamic survey andcorresponding to peaks of the ASDs placed at 0.76, 1.25, 1.66, 1.90

and 2.78 Hzare also apparent in Figure 5 which also shows

that a linear correlation exists between the mode order n and the

corresponding natural frequency fn of stay cable S12

. Hence, the

tension force T can be obtained from natural frequencies and cable

properties. The application of the taut string tension force equation,

T(fn) = 4rL2(f

n/n)2 to the cable S

12 resonant frequency results

(cable length L = 57.24 m, cable weight/m r = 36.51 kg/m and

resonant modes 1-5) is summarized in Table 1. The estimates

of cable tension obtained from resonant frequencies of the

accelerometer and radar sensor are virtually equal. A tension force

of 2694 kN was measured by a load cell which compares very well

with the average force of 2689 kN for the IBIS-S.

Figure 4.(a) Typical displacement time-history (blue) by the IBIS-S

on cable S'12 with (b) typical acceleration data overlaid on top (red).

a

b

Figure 5.Auto-spectrum displacement data comparison of the IBIS-S

radar (orange) and accelerometers (blue)on cable S'12

SENSOR T(f

1)

(kN)

T(f1)

(kN)

T(f1)

(kN)

T(f1)

(kN)

T(f1)

(kN) Average

Accelerometer 2679 2707 2660 2693 2690 2686

IBIS-S Radar 2679 2707 2679 2693 2690 2689

Table 1.Tensions in cable S'12

obtained from accelerometer and IBIS-S radar measurements.

Test Results

CASE HISTOR


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CASE HISTORY

Figure 2.IBIS-S position in the survey for thdownstream surveys.

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A2

Testing Procedure

Microwave remote sensing was used to perform dynamic

measurements on the arrays of forestays supporting the deck of

the cable-stayed bridge crossing the river Oglio between the towns

of Bordolano and Quinzano (Fig.1), about 70 km far from Milan,

Italy. The dynamic characteristics of the bridge were well-known

since ambient vibration tests were carried out in Spring 2004 by the

Vibration Laboratory of LAquila University using Sprengnether

servo-accelerometers. During this test, 10 global modes of the

bridge were identified in the frequency range 010 Hz and also the

dynamic response of one cable (S2U

in Fig.1) has been recorded.

The deflection response of the two arrays of cables to wind and

traffic excitation was quickly and safely acquired by positioning

the IBIS-S at the base of the upstream-side and downstream-side

tower, respectively (Fig.2). Since the test scenario on the two sides

was practically the same, the radar image profiles are very similar

and each range profile exhibits three well defined peaks, occurr i

at the expected distance from the sensor (Fig.3) and clear

identifying the position in range of the cables.

Dynamic Measurements on the Forestays of a Cable-stayed Bridge

Figure 1.Stay-cable comparison of the auto spectrum displacement data for the IBIS-Sradar and accelerometer.

Figure 3.Range prole data of the test scenario of the downstream

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2

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Project: Bordolano cable-stayed bridge

Project Location:Bridge over the Oglio River, Italy

Bridge Construction:Steel composite deck, double-plane cables andtwo inclined concrete towers. Elevation and plan views of the bridge and

typical cross section are presented in Figure 1.

Project Scope:The two main arrays of bridge forestays were surveyed,with the main goal of verifying the ease of set-up, and the operational

simplicity provided by the IBIS-S microwave remote sensing equipment.


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CASE HISTOR

Dynamic Measurements on the Forestays of a Cable-stayed Bridge A2

For each array, 3000 s of radar data were acquired at a rate of 200 Hz;

the displacement time-history collected on stay-cable S2U

is shown

in Figure 4. Figure 5 presents a direct comparison between: (1) the

auto-spectrum of the acceleration measured on stay-cable S2U

by a

conventional accelerometer in the test of Spring 2004 and (2) the

auto-spectrum of the acceleration obtained from the radar sensor

(and computed by twice differentiating the IBIS-S displacement

data). The inspection of the spectral plots in Figure 5 clearly reveals

that the values of the first seven natural frequencies of stay-cable

S2U

, identified on the basis of the auto-spectra obtained using

conventional and radar measurement systems are virtually coincident

(1.84, 3.70, 5.53, 7.37, 9.24. 11.1 and 12.93 Hz in Fig.5). In addition,

the peaks of the ASDs placed at 1.06, 2.18, 4.25 and 6.03 Hz

correspond to the global natural frequencies of the bridge, identifiedin the previous dynamic survey of the bridge in 2004.

The inspection of the ASDs in Figure 5 clearly highlights that, as

expected, the natural frequencies of the corresponding cables on

the two opposite sides; S1US

1D, S

2US

2D and S

3US

3D(Fig.1) are

almost equal. The response of all cables is characterized by a large

number of equally spaced and well-defined peaks so that the tension

forces can be computed from cables natural frequencies using the

taut string model; application of this approach leads to values of

cable tensions summarized in Table 2 and very close to the design

values. Finally, Figure 6 shows how close the experimental resonant

frequencies obtained from microwave remote sensing are to the

predictions of the taut str ing model.

Test Results

Figure 4.Deection time-history measured by the radar sensor on thestay cable S

2U.

Figure 5.Auto-spectrum displacement data comparison of the IBIS-Sradar (orange) and accelerometers (blue)on the stay-cable S'

2u.

Figure 6.Experimental and taut-string based natural frequencies of:(a) upstream side forestays and (b) downstream forestays.

Upstream Forestays

a

Downstream Forestays

b


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CASE HISTORY

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A3

Testing Procedure

The IBIS-S system was deployed under the bridge superstructure

(shown top left), illuminating ve corner reectors installed on

the west side of the bridge between two bridge piers. The eld set-

up and all data acquisition required less than 1/2 day. Due to the

non-contacting nature of the system and operational range, all

testing was performed with no trafc disruption and minimal

support requirements.

Each of the corner steel sheet metal reectors produces a sharp

peak on the IBIS-S range prole and therefore a good quality

data point whose displacement can be measured by analyzing the

phase variations with the differential interferometric technique.

Figure 3 presents the IBIS-S Power Prole; a high level of

backscattered signal in the range bin in which a crossing beam

is located gives a high Signal to Noise Ration and therefore, high

accuracy in the measurement of the displacement. The vertical

displacements of the ve metallic corner reectors installed on

the west side of the bridge (Fig.3) during the test set-up phase are

presented in Figure 4, which shows the resulting displacement

from the passage of a testing truck and other vehicles over the

bridge deck. The maximum measured peak to peak displacement a

mid-span is 2.26 mm. Vertical velocity vibration amplitudes of the

measurement points range from +/-4 mm/sec, depending on truck

speed. The velocity spectra (Fig. 5) shows six sharp frequency

peaks at 1.3, 2.05, 2.45, 2.95, 3.35, and 3.55 Hz, corresponding to

the structural resonance modes. The rst three should correspond

to mainly exural modes while the second three should be related

to the torsional modes. Further analysis could be performed by

importing the IBIS-S Displacement Time Series into specic

software for ambient modal vibration structural analyses to

evaluate, for example, the resonant frequencies, vibration mode

shapes and damping.

Static Displacement and Dynamic Vibration Monitoring of a Concrete Bridge

Figure 1.System conguration and survey geometry of the post-tensioned box girder bridgeover Interstate 70 in Colorado, USA.

Figure 2.Installation of the 5 metallic cornerreectors due to the smooth concrete surfaceeach at about 7.5 m spacing (Fig.1).

Project: Flyover Exit Ramp from I-70 EB to CO HWY 58 WB

Project Location:Golden, Colorado USA

Bridge Construction:Post-tensioned concrete box girder bridge

The system configuration and survey geometry is shown in Figure 1.

Project Scope:Primary objective of the demonstration was to measure the deectiontime-histories and maximum deections of the bridge under normal auto and truck

trafc loading. Metallic corner reectors were mounted at 5 locations to monitor

vertical dispacements and vibrations.

Reference:Olson, L.D., Innovations in Bridge Superstructure ConditionAssessment with Sonic and Radar Methods, ASNT, NDE/NDT for Highways and

Bridges, Structural Materials Technology Conference, LaGuardia, NY (August 2010).

Corner Reflectors

MetallicCorner

Reflectors


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CASE HISTOR

A3Static Displacement and Dynamic Vibration Monitoring of a Concrete Bridge

Figure 4.Vertical displacements of the ve passive metallic reectorsinstalled on the bridge caused by random vehicles and a 55,000 lb. testtruck (shown) passing over the bridge deck.

IBIS-S POWERPROFILE

A sharp peak corresponding

to each corner reflector on the

bridge is clearly identified in

the profile.

Figure 3.Portion of the IBIS-S Power Prole from radar reections from the ve metallic cornerreectors (CR1-CR5).

Metal Corner Reflector

Figure 5..Velocity Frequency Spectrum for the 5 corner reectors fromdisplacement time domain data showing 6 resonances.


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CASE HISTORY

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Testing Procedure

A4

A demonstration test was performed using the high precision IBIS-S

radar system, which was deployed on the Brooklyn side bank below

the bridge superstructure (Fig.2). The eld set-up and all data

acquisition required less than 1/2 day for the IBIS-S radar system.

Due to the non-contacting nature of the system and operationalrange, all testing was performed with no trafc disruption and

minimal support requirements.

Two tests were performed pointing the

sensor rst towards the center and then to

the edge of the main span with an attempt to

estimate the torsion given by the asymmetric

conguration of the trafc. In both situations,

the IBIS-S radar system was placed under the bridge (Fig.2) on

the Brooklyn side illuminating most of the main span with the

radar beam, therefore allowing the accurate displacement measure

ment of around 80 visible points along the bridge span at the same

time (steel cross beams at 5.5 m spacings). The excellent natural

reectivity of the micro-wave from the steel oor beams provided

equally distributed measurement points along the tested span witho

the need for articial reectors, oftentimes required for concrete

other non-metallic structures. Each of the oor beams generated

sharp peak on the IBIS-S range prole and therefore a good quali

point whose displacement can be measured by analyzing the phavariations through the differential interferometric technique.

Figure 2.View of the IBIS-S system setupon the Brooklyn side bank below the bridgesuperstructure.

Static Displacement and Dynamic Vibration Monitoring of a Steel Bridge

Project: Manhattan Bridge

Project Location:Brooklyn Borough, New York City, NY USA

Bridge Construction:Steel truss and suspension cable bridge weighingover 14,680 tons. The bridge traffic layout is shown in Figure 1.

Project Scope:The primary objective of the demonstration was tomeasure the deection time histories and maximum deections of

the centerline and north edge of the Manhattan Bridge under normal

automobile/truck and subway train trafc loading. A comparison test was

made with previously collected displacement data from Global Position

System (GPS) measurements versus IBIS-S radar system displacements.

Reference:L. Mayer, B. Yanev, L.D. Olson, A. Smyth, Monitoring ofthe Manhattan Bridge and Interferometric Radar Systems, IABMAS 2010

Proceeding, Philadelphia, PA USA (June 2010)

Figure 1.Current Manhattan Bridge trafc layout: cross-section shown facing north.


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A4

CASE HISTOR

Static Displacement and Dynamic Vibration Monitoring of a Steel Bridge

Figure 3 presents a portion of the IBIS-S Power Prole: a high level

of backscattered signal in the range bin in which a cross oor beam

is located gives a high Signal to Noise Ratio and therefore high

accuracy in the measurement of the displacement.

Figure 4 shows the vertical displacement of the central section of

the floor beams in the main span resulting form the passage of a

single train over the deck. The measured peak to peak displacement at

mid-span is 33.82 cm but it decreases moving towards the bridge piers.

The slow train entrance can be clearly identified by the high delay

between the maximum vertical deflections of points at the different

cross-sections of the span. Further, a positive vertical deformation of

5.31 cm can be observed when the train passes to the side spans.

Measured peak to peak vertical deformations were about 1 cm under

normal vehicular traffic when no trains were on the bridge.

Maximum peak to peak deformations measured during the passage

of more than one train both for the central and side section of the

main span are shown in Figure 5. Both deformed static curves are

close to symmetrical with respect to the center of the span. However,

the one related to the edge measurement shows a maximum deflection

value at mid-span which is 6.67 cm higher than the one measured for

the central section. Because the scans were taken at different times,

the difference between the maximum deflections mid-span must be

considered as a lower bound of the torsional movement. The center

of the cross section would not be at its lowest during the greatest

torsional deformation. Further, Figure 5 shows significant torsionalbehavior at quarter-span related to the second torsional mode, as

should be expected.

Jointly analyzing the results in the frequency domain through the

computation of the Displacement Cross-Spectrums of the whole set

of range bin combinations and averaging the results allows the

identification of the frequencies which are common to all

measurement points, excluding frequencies potentially given by

scattered noise effects. This kind of spectral analysis on the

displacement time series, measured both for the central and for the

side section, leads to the clear identification of three main resonant

structural frequencies. As shown in Figure 6, the first resonant

frequency is at 0.23 Hz, the second one is at 0.30 Hz while the thirdis at 0.49 Hz.

The frequencies obtained by the GPS were 0.23 Hz, 0.31 Hz

and 0.50 Hz respectively. Further, a resonant frequency peak at

0.016 Hz can be identified and was shown to be related to the slow

static deformation of a passing train. Also, similar magnitude of

displacements were measured by the earlier GPS measurements by

Columbia University to the IBIS-S displacements.

Test Results

Figure 3.Portion of the IBIS-S Power Prole.

Figure 4.Vertical displacement time series of the crossing beamsgiven by the passage of a single train over the deck.

Figure 5.Peak to peak vertical deection of the central and sidesections of the main span from trains from maximum IBIS-Smeasured displacements of 80 oor beams.

Figure 6.Average displacement frequency spectra showing 3resonances.


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CASE HISTORY

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Testing Procedure

A5

Figure 2. (a) Corner reectors on left adjacent to accelerometer sensorand (b) IBIS-S located under Capriate bridge near pier in circle above

Ambient Vibration Testing for Modal Analysis

Two series of ambient vibration tests were conducted and the

response of the bridge was measured at selected points using

WR-731A piezoelectric sensors for comparison with IBIS-S

measurements of 6 corner reflectors. Figure 1 above shows a

schematic diagram of the vertical sensor layout. A series of three

set-ups were required to cover the measurement points identified

in Figure 1, with the accelerometers placed at points 5-6, 21-22

being used as reference measurements; the same figure identifies

the locations of the corner reflectors installed on the downstream

side of the deck (Fig.2a). As shown, both accelerometer and corner

reflectors were positioned as closely as possible to each other.

Figure 1.Accelerometer Sensor and Corner Reector layout for ambientvibration testing of the Capriate bridge (dimensions are in m).

Project: Capriate Bridge, Italy

Project Location:Traffic bridge crossing the Adda River between thetowns of Capriate and Trezzo

Bridge Construction:Multi-span concrete arch bridge

Project Scope:A comparison was made using accelerometers and theIBIS-S radar system for ambient vibration testing to determine modal

vibration frequencies and shapes.

a b


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CASE HISTOR

A5Ambient Vibration Testing for Modal Analysis

The range profile of the stronger reflectors, including the six cornerreflectors, is shown in Figure 3.

Typical velocity signals recorded for the accelerometer at TP22 on

the downstream side and the adjacent corner reflector of the IBIS-S

system are superimposed on each other in Figure 4. Review of this

figure indicates an excellent agreement between the accelerometer

(integrated to velocity units) and the IBIS-S (differentiated to

velocity units).

Frequency domain comparisons of the IBIS-S and accelerometer

are presented in Figure 5. Again, there is an excellent agreementbetween the two systems with the IBIS-S having the advantage of

faster setup time and remote monitoring (no cables) of the

displacements and vibrations.

Two of the vibration modes apparent in Figure 5 are plotted for

all 6 corner reflectors versus the accelerometer responses in

Figure 6. Review of this figure shows that the IBIS-S data agrees

very well with the accelerometer derived mode shapes and

frequencies. The evaluation of the modal parameters from

the radar signals was fi rst carried out by applying the Frequency

Domain Decomposition (FDD) technique to all available

velocity records obtained by the IBIS-S. The use of a greater

number of corner reflectors would have thus fully defined the

mode shapes for the bridge just as was done with the

accelerometers which are more fully plotted in Figure 6.

Test Results

Figure 3.Range prole data results from the downstream side.

Figure 4.Comparison of velocity (mm/s) vibration responses versustime (14 s) comparison for the accelerometer and IBIS-S cornerreector measurements at TP22.

Figure 5.Comparison of frequency domain responses from 3000seconds of data between the IBIS-S and Accelerometer.

Figure 6.Modal shape comparison with IBIS-S and Accelerometer.


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CASE HISTORY

Project: Bordolano cable-stayed bridge #2

Project Location:Bridge over the Oglio River, Italy

Bridge Construction:Steel composite deck, double-plane cables and twoinclined concrete towers. Elevation and plan views of the bridge and typical

cross section are presented in Figure 1.

Project Scope:The two main arrays of bridge forestays were surveyed, withthe main goal of verifying the ease of set-up, and the operational simplicity

provided by the IBIS-S microwave remote sensing equipment.

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Testing Procedure

A6

Figure 2.The existing transversal beamacted as natural reectors, and wereexploited as measurement points.

Dynamic Monitoring of Vertical Displacements Caused by a Train

A measurement was performed on a bridge of the Kuranda Scenic

Railway using the IBIS-S radar system. The IBIS-S was installed

2.7 m below the bridge deck (Fig.1) in order to measure its deflection

during the passing of the train. The existing transversal beams of

the bridge could be exploited as measurement points (Fig.2).

The IBIS-S radar system illuminated the entire metallic portion of

the bridge from below. In Figure 3, it is possible to see the radar

image of the bridge. Every peak in the image is an exploitable

measurement point. A total of 18 peaks occured between 16 and

41 m which correspond to the beams on the central span.

The whole measurement consisted of 2 sessions of 10 minutes each

across two train passages. The results from the first measurement

session in terms of displacement vs time and frequency analysis of

the measured displacements are shown on the next page.

Figure 1.The IBIS-S system was installed under the bridge (circled area) in order to measure itsdeection during the passage of a train.

Project: Scenic railway bridge, completed in 1891. It is said to be the

most photographed bridge in all of Australia.

Project Location:Kuranda Scenic Railway, Cairns, AU

Bridge Construction:Winding its way through dense rainforest, steepravines and picturesque waterfalls, this steel trestle railway incudes over

49 bridges and 19 hand-made tunnels.

Project Scope:The IBIS-S radar system was utilized to determine themaximum displacement of the now century old bridge for accessing

the current stress and fatigue of the bridge deck. The experimental

results consist of the visualisation of the bridge deck displacement; and

identification of the resonance frequencies of the structure.

Operational Parameters

Maximum Range Distance 120 m

Sampling Frequency 70 Hz

Spacial Resolution (in range) 0, 5

Measurement Parameters

Test Width (across train passage) 10 ft

Bridge Length ~ 50 m

Bridge Deck Height (above IBIS-S) 2.7 m


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CASE HISTOR

A6Dynamic Monitoring of Vertical Displacements Caused by a Train

Figure 4.A frequency was obtained by applying the frequencyanalysis to the measured displacements linked to a train passage.

Figure 5.Line of Sight displacement projected along the vertical direction, according to the radar tobridge measured distance (2.7 m).

Figure 3.IBIS-S radar range prole of the illuminated rail (Fig.2).

Steel pillar

1/4 Bridge Length 1/2 Bridge Length

Steel pillar End of Bridge

IBIS-S Radar Range Profile

BRIDGE

Test Results


20/20

Corporate Office:

12401 W. 49th Avenue

Wheat Ridge, CO 80033-1927 USA

Toll Free: 1.888.423.1214

Ph: 303.423.1212

Fax: 303.423.6071


www.OlsonInstruments.com

www.OlsonEngineering.com

Olson Instruments , Inc .

Olson Instruments, Inc. is a distributor for IDS Georadar instruments in the USA

Southwest Office:

800 Liles St.

Socorro, NM 87801 USA

Ph: 575.838.2433

Fax: 303.423.6071




Northeast Office:

47 Orient Way, Suite 2C

Rutherford, NJ 07070 USA

Ph: 201.933.3777

Fax: 201.933.8050




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