Structural Health Monitoring of Bridges - IIBE

Presentation on

Structural Health Monitoring of Bridges

Dr. Abhay BamboleProfessor

Department of Structural Engineering

Veermata Jijabai Technological Institute (VJTI)

Matunga, Mumbai,

[email protected]

ORGANIZED BY

Indian Institution of Bridge Engineers – IIBE

in association with

Department of Structural Engineering, VJTI 24th October 2018

IIBE Lecture

2

What is Structural Health Monitoring (SHM)

“The process of implementing a damage

detection and characterization strategy for

engineering structures”

SHM Involves:

➢Health monitoring

➢Operational Evaluation

➢Data Feature Extraction

➢Statistical Models Development

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Structural Health Monitoring

Human body like a structure. Damage or problem with body, the unhealthy condition is detected by the nervous system and it signals is sent to brain.

Synonymously the sensors act as the nervous system and the acquisition system act as a brain. The Structural expert is like an doctor for the structure who deices the SHM system and listens to the responses and proposes a solution/repair strategy.

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Health Monitoring of a Patient in ICU

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Health Monitoring of a Bridge in ICU

Wearable Body Area Network

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Smart Wearable Health Monitoring

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Bandra-Worli Sea LinkVidyasagar Setu in Kolkata,

the longest cable-stayed bridge of India

Chenab bridge, world’s highest rail bridge,Pamban Bridge is India’s first sea bridge

Bridges in India

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List of Revised Master Plan corridors proposed

Sr. No. Corridor Length (Km)

1Versova-Andheri-

Ghatkopar

11.40

2Dahisar-Charkop-

Bandra-Mankhurd

40.00

3Colaba-Bandra-SEEPZ

(Andheri)

33.50

4

Wadala-Ghatkopar-

Mulund-Thane-

Kasarwadavali

32.00

5 Bhiwandi-Kalyan 23.10

6

Jogeshwari Vikhroli

Link Road-SEEPZ-

Kanjurmarg

10.50

7Andheri (East)-Dahisar

(East)

18.00

8 Sewri- Prabhadevi 3.50

Total 172.00

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SHM – Some Case Studies

The three-tower suspension bridge,

with two main spans of 1,080 m each

and side spans of 390 m, crosses the

Yangtze River

Monitoring of the Taizhou Yangtze River Bridge

Robo-Control monitoring system - user interface on the internet.

Presentation of measured data (graph form).

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A new cable stayed bridge on Yamuna River

in Wazirabad, Delhi, length of 675 metres,

with a main span of 251 metres. Its steel-

concrete composite deck

Signature Bridge, Wazirabad, Delhi

A total of 104 sensors, usingdata 171 channels, to measureenvironmental, load andstructural response factors

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The Hunter Expressway is situated in mining

area. The bridges on the new road are at risk of

settlement due to mining subsidence, The

structures are mainly concrete box girder

bridges

Hunter Expressway Bridges, Australia

Data is measured and recorded at the abutments and piers:i. At the abutments: displacement in longitudinal and transverse direction of theexpansion joint, settlements and temperatureii. At the piers: settlements relative to the right or left abutment and temperature

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Monitoring of Hunter Expressway Bridges, Australia

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Motivation for Structural Health Monitoring

▪ Move from time-based maintenance to condition-based maintenance

▪ Combat asset readiness

▪ New business models, Manufacturers of large capital investment hardware can charge by the amount of life used instead of a time-based lease.

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Objective, Needs and Benefits of SHM

• Monitor the in-situ behaviour of a structure accurately and efficiently to assess its performance under various service loads, to detect damage or deterioration, and to determine the health or condition of the structure.

•The SHM system should be able to provide, on demand, reliable information pertaining to the safety and integrity of a structure.

•The information can then be incorporated into bridge maintenance and management strategies, and improved design guidelines.

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Static Response based SHM

Static-Based SHM

• Based on the premise that damage will alter the static

properties of the structure.

– e.g. displacements, rotations

• Drawback

Considerable static deflection requires

large amount of static force

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Vibration-Based SHM

• Based on the premise that damage will alter the dynamic

properties of the structure.

– e.g. structural response, frequencies, mode shapes, damping

or modal strain energy change

• By measuring the structural response by means of sensors

strategically placed on the structure, and intelligently

analyzing these measured responses, it is possible to

identify damage occurrence.

• It can be done either in modal domain or physicaldomain

Dynamic Response Based SHM

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Advantages and positive ramifications of including SHM in civil structures

1. Confirm the design parameter: Detection of damages during construction which can cause any change in properties than expected by design.

2. Quality Assurance: By providing continuous and quantitative data, a monitoring system

3. Complex Structures are well managed: Learning how a structure performs in real Conditions

4. To Ensure safety of people, nature and property: Early detection of performance Degradation

5. Monitoring reveals hidden resources: Many times the structure performance is better than what it is designed for and this gives an extra freedom to play with for further designs and construction.

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Steps Involved with SHM

▪ Identify structures needing monitoring

▪ Acquire information on probable degradation mechanisms and risks from design engineers or owners of structure.

▪ Establish expected responses to degradations.

▪ Design SHM system to detect such conditions and select appropriate sensors.

▪ Install and calibrate system.

▪ Acquire, Analyse and manage data. This involves alarming the concerned people whenever there is an emergency.

Vibration Based SHM: Sensors• Different forms of dynamic structural response:

– Displacement, Velocity, Acceleration,Strain.

– Which ones to measure depends on monitoring conditions and

objectives.

• Sensing technology: an ever emerging field of study

• Based on what to measure, different sensors available:

– Laser Displacement Sensors (LDS)

– Velocity Transducers

– Seismometers

– PiezoelectricAccelerometers

– Strain Gauges

• Most of these sensors can be wirelessly connected 14

Accelerometer (Acceleration)

Load Cell (Force)Displacement Sensors

Strain Gauge (Strain)

Collection of Sensory Information21

SENSORS

Foil type Strain GagesCrack Openings / Strain sensors

Temperature sensors

http://www.omega.com/ppt/pptsc_lg.asp?ref=gen_purpose_strain_SG&Nav=

Monitoring of Cable stayed Bridges

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Adige Bridge, Italy

Elasto-Magnetic Sensors

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Bridge Health Monitoring System Using Advanced Laser Technology & Accelerometer

Bridge Health

Monitoring

Hardware SoftwareData

Analytics

Hardware

MicrocontrollerWifi mopdule Sensors

Laser

[range 80m, accuracy 1 1mm]

Accelerometer

Temperature & Humidity

[DHT11]

[DS18B20]

Single Board Computer WiFi Router / GPRS

Server / Cloud

# Nomenclature Technique Purpose Follow-up

1 Deflection (Distance) Measurement

Ultrasonic Sensor[HC SR04]

It won’t shine any light on the surface of referenceMicrocontroller has many additional ports available, hence this can be parallelly attempted in addition to Laser Sensor for R&D comparison purpose

Price is Rs. 99 to Rs. 120

2 Deflection (Distance) Measurement

Microwave radar Microwave radar is presently used in Large Petrol storgage in Reliance, Adani Petroleum division, etc

Data sheet, resolution and price needs to be explored

3 Camera IP Camera Capture the vehicle number plate,when the acceleration sensor sensing certain threshold value

Data sheet of IP Camera needs to be explored

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Scope for Near future possible R&D - Prototype Version 2.0

Laser

Accelerometer

Temperature & Humidity

[DHT11]

[DS18B20]

Microcontroller Wifi module Single Board

Computer

Server / Cloud

Sensor Node

WiFi / GPRS

WiFiRout

er

WiFiRout

er

Wireless protocol 802.11

Development of indigenous wireless sensor node (Displacement, Acceleration, Temperature)

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Amar Mahal Flyover

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Installation of Sensor node on Amar Mahal Flyover

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28 November 2018 34

DAMAGE LOCALIZATION

Determining location of crack/damage from frequencies is a difficult task.

Cracks/ damage at two different locations may cause the same amount of frequency change. Therefore parameter other than frequency need to investigated and studies which shall enable to identify the location of damage in structure.

Curvature mode shape of the structure may be used for establishing damage location.

The difference in the curvature mode shapes between intact and the damaged case is utilized to detect the location of crack in the structure.

28 November 2018 35

CURVATURE MODE SHAPES

Curvature mode shapes are related to the flexural stiffness of

the beam cross-sections.

Curvature at a point is given by:-

ʋʺ =𝑀

𝐸𝐼Where,

ʋʺ= Curvature at a section

M= Bending moment at a section

The changes in the curvature are local in nature and hence can

be used to detect and locate a crack in the structure.

28 November 2018 36

CURVATURE MODE SHAPES

The change in curvature increases with the reduction

in the value of (EI), and therefore, the amount of

damage can be obtained from the magnitude of

change in curvature.

The curvature mode shapes are obtained from the

displacement mode shapes through central difference

approximation

Where, h is the length of the element

Finally the difference in the curvature mode shapes

between undamaged and the damaged case is used to

detect location of the crack.

ʋʺ = ʋ𝑖 +1−2ʋ𝑖

+ʋ𝑖−1

(ℎ2)

Study of damaged and undamaged steel beam

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28 November 2018 38

DAMAGE LOCALISATION BY CURVATURE DIFFERENCE METHOD

Case 1: Location of Damage 1

The location of damage 1 (Flange cut of 50mm in the centre)

studied by plotting the absolute curvature difference between

damaged and undamaged condition. Higher modes are more

sensitive to damage than lower modes.

28 November 2018 39


It is clear from the above plots that difference between

the absolute curvature of damage and undamaged,

helps in depicting the exact location of damage.

28 November 2018 40



The location of damage 2 (100mm cut on bottom flange at

the centre (i.e. at 3000mm)) found by plotting the absolute

difference curvature of damage 2 with the undamaged

condition.

28 November 2018 41


The difference increases with the reduction in the stiffness

of the damaged zone. Therefore, one can analyse the degree

of damage from the difference in absolute curvature mode

shape.

28 November 2018 42



The damage 3 contains web crack of 50 mm x 50 mm at the

quarter span i.e. at the location of 1500 mm. The absolute

curvature for Damage 3 conditions are plotted as shown

below

28 November 2018 43

DAMAGE LOCATION:-CURVATURE DIFFERENCE METHOD

The above plots speaks that some damage is observed near

1500mm i.e. this method also helps in depicting the

damages in the web portion.

Optical fibre based measurement of Curvature

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Case Study-IMonitoring of Structural Rehabilitation of

the Karal Bridge

ROB ( Rail Over Bridge ) at Karal, JNPT, Navi Mumbai

Structural Details Bridge is made up of beam-slab RCC system (Pre-cast beams) with diaphragm

beam.

Each span consists 8 no. of beams/girders of an average length of 16m.

36 spans of varying lengths having 37 expansion joints in this bridge. Total length 700 m.

2400 2400 2400 2400 2400 2400 2400 2400

Main Girders

Diaphragm

Plan

180 mm

2400

mm

1120 mm

8-32mm

Monitoring

❖ Monitoring of Deflection: As the primary indicator of the strengthening effect.

❖ Monitoring of flexural strain: To measure strengthening effect with regard to enhancement in flexural stiffness of girders.

❖ Monitoring of shear strain/crack width: To measure strengthening effect with regard to enhancement in shear stiffness of girders.

❖ Monitoring of vibration: Frequency measurement will indicate the strengthening effect with regard to enhancement in overall stiffness superstructure.

Different sensor used

Foil type Electric Resistance Strain

Gage

Linear Potentiometer for

Displacement Measurement

Piezoelectric Accelerometer Omega Type Displacement

Transducer

Strain gauge at the Bottom of the Beam Soffit to measure Flexure strain gage

Deflection Sensor at the Bottom of the Beam Soffit

Omega type Displacement Transducers at the surface of the Beam

at an angle of 45

Piezoelectric accelerometers at the Bottom of the Beam Soffit

shear strain gauge at the surface of the Beam at an angle of 45ο

Dummy Gage for Temperature Compensation

Instrument use for Data Acquisition

Load case 7 and 8 – For Vibration

Results

Span-1 Span 2 Span 3

Before

strengthening5.38 mm 5.18 mm 5.08 mm

After

strengthening3.93 mm 3.65 mm 3.95 mm

Reduction in

defection1.46 mm 1.53 mm 1.13 mm

% reduction in

deflection-27.10% -29.50% -22.20%

Average Central Deflection (mm)

Span 1 Span 2 Span 3

Before

strengthening450 µε 407 µε 311 µε

After


Reduction in

Flexural Strain262 µε 219 µε 151 µε

% Reduction in

Flexural Strain-58.20% -53.80% -48.50%

Average Flexural Strain (µε)


Before


After


Reduction in

Shear Strain38 µε 52 µε 47 µε

% Reduction in

Shear Strain47.5 (%) 57.8 (%) 65.3(%)

Crack Width of Diagonal Cracks near Support(Change in change width over a gauge length of 200mm in µε)


Before

strengthening5.301 Hz 5.344 Hz 5.520 Hz

After

strengthening5.737 Hz 5.964 Hz 5.833 Hz

Increase in

Fundamental

Frequency

0.436 Hz 0.620 Hz 0.313 Hz

% Increase in

Fundamental

Frequency

8.2 (%) 11.6 (%) 7. (%)

Natural Frequency of Vibration (Hz)

Case II

Monitoring of Deflection and Strains in Transfer Girders of Proposed Hotel Building at Mumbai

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Progress of Construction work

http://img860.imageshack.us/i/20110520190655.jpg/

http://img684.imageshack.us/i/photo0770f.jpg/

Layout of sensors

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Embedded strain gages

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Surface strain gage

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Girder

No.

Flexural strains at the

Soffit of beam in mid section

Shear strains at 1.25 M

depth near supportCentral Deflection

Theoretical

value

Measured

value

Theoretical

value

Measured

value

Theoretical

value

Measured

value

3 163.4 µε 67 µε 31.29 µε 47 µε 10.7 mm 13 mm

4 164.6 µε 74 µε 31.49 µε 56 µε 10.75 mm 10 mm

Monitoring of Strains and Deflections of Girder:Reading due to self weight of Girders after release jacks

Case IIIMonitoring of Deflection and Strains in Mahatma

Gandhi Setu at Patna During Rehabilitation

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Ganga Setu Instrumentation

Location of Strain Gauges

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Bridge Girder Deflection Measurement

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Span No.

Average micro strains of Top

section

Average micro strains of

Bottom section

AT/FT BT/ET CT/DT AB/FB BB/EB CB/DB

P-28 -25 -17.0 -52.0 -14.5 +18 +19.5

P-29 -19.0 -38.5 -60.5 -31.0 -21.0 -33.0

P-26 -28.9 -35.15 -48.0 - - -4.0

P-25 -16 -33.5 -34.5 -14 - -

P-35 -20.2 -18.7 -18.3 -9.0 -13.4 -14.7

P-34 -14.5 -40.5 -39.5 -23.5 -41.5 -12.5

P-23 -17.65 -43.05 -60.45 -21.2 -24.7 -7.45

P-16 -98.75 -63.0 -69.8 -5.2 -28.0 -6.5

P-2 -29.3 -13.7 -24.3 -31.5 -41.7 -10.8

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Reduction in Tension Strains: Strain monitoring

Uplift of Cantilever Ends: Deflection monitoring

Span No. Location

Uplift recorded at

end due to stressing

only in mm

Uplift recorded at

Hajipur end due to

stressing only in mm

P-28 Upstream carriageway 21.7 26.7






P-23 Upstream carriageway 10. 3 11.0



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PWD Maharashtra

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LOCATION

This flyover is located at Turbhe junction of Navi Mumbaiwhich connects Mumbai to Thane & Panvel

Turbhe Flyover is an important link between Mumbai-PuneHighway

Mumbai

Thane

Panvel

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LAYOUT PLAN OF TURBHE FLYOVER

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Typical single cell trapezoidal box girder section of Turbhe Bridge

VISUAL OBSERVATION

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Undulations on riding surface due to central sagging

Sagging of crash barrier Side view of deformed girder

DEFLECTION MEASUREMENT BY TOTAL STATION

An average of Permanent Deformation of

110 mm was observed against theoretical

value of 25mm (deformation due to self wt.)

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Prism placed at support

Prism placed at mid span

Deflection measurement by Total Station

Visual observation

VIBRATION MEASUREMENTS

▪ The objective of vibration testing is to co-relate the defects in

the bridges due to the changes in its dynamic characteristics.

The vibration analysis of a structure carried out over a period

of time measures loss of stiffness and not the loss of strength.

▪ Accelerometers are temporarily attached to the bridge and the

traffic induced vibrations are recorded. The modes of vibration

and damping can then be determined by computerised analysis.

▪ Natural frequency (f) of simply supported beam is calculated

by

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Non destructive test

Where,

n = mode number

l = length of beam

E = modulus of elasticity

I = Second moment of area

𝝆 = Mass per unit length

21

2

n EIf

l

=

VIBRATION MEASUREMENT SETUP

Response of girder

OROS (Vibration Measuring Instrument)

INFERENCE:•Avg. Natural frequency of girders found to be 2.8125 Hz which is less than the

theoretical value of 4.903 Hz.

•This shift in natural frequency indicates overall loss in stiffness of the girder due to

presence of numerous cracks and degradation of material.

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Non destructive test

Accelerometer installed at soffit of

girder for vibration measurement

Class 70R Loading Support Condition

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Finite Element Model

UPDATION OF FEM MODEL

▪ Considering existing deteriorated condition of concrete the FEmodel was updated.

▪ The present condition of bridge superstructure have numerouscracks which leads to significant decrease in stiffness of girder aswell as dynamic parameters such as natural frequencies.

▪ The results from FEM after updating the model were matchingactual field test values.

▪ Simulating the existing condition of superstructure is necessary tocheck the effectiveness of strengthening with FRP rather thanapplying it on ideal conditions of girder which do not exist on site.

▪ This updated FE model of girder was used to modelstrengthening with FRPC wraps and laminates.

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FEM analysis

DEFLECTED SHAPE

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FEM analysis

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FREE VIBRATION ANALYSIS RESULTS

NATURAL FREQUENCY OF VIBRATION

Idealized 7m box girder model Natural Frequency (Hz)

Before strengthening 4.8295

After strengthening 5.0502

(%) Increase in natural frequency 4.4%

Updated 7m box girder model Natural Frequency (Hz)

Before strengthening 2.8484

After strengthening 3.0767

(%) Increase in natural frequency 8.01%

Experimental value of natural frequency = 2.8125 Hz

FEM analysis

SENSORS

Strain Gages

Linear Potentiometers, LVDT -Displacement

Thermocouples-Temperature

Accelerometers – Modal vibration

Tiltmeters

◦ Uni-axial

◦ Bi-axial

Crack Openings

http://www.omega.com/toc_asp/subsectionSC.asp?subsection=A02a&book=Temperature

http://www.omega.com/ppt/pptsc_lg.asp?ref=gen_purpose_strain_SG&Nav=

Thank you.

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Structural Health Monitoring of Bridges - IIBE

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