NON DESTRUCTIVE STRUCTURAL ASSESSMENT OF BRIDGES USING IN-SERVICE DYNAMIC RESPONSE

Introducing Mainmark

• Mainmark offers unique, innovative services for rectifying

problems in residential, industrial, commercial, civil engineering

and mining situations.

• For over 20 years Mainmark has led the world in developing

and offering the most advanced and accurate systems of geo-

polymeric injection techniques for ground engineering.

• Due to the knowledge gained from experience we provide

solutions that reduce lost production time, improve productivity,

and improve the longevity of your asset and are safer to install.

• Mainmark have joined with STRAAM to offer the STRAAM

system into Australia, New Zealand and Japan

Introducing MainmarkGlobal Footprint

Australia:

Sydney, Melbourne,

Brisbane, Adelaide, Perth

New Zealand:

Christchurch, Auckland

Thailand:

Bangkok

Malaysia:

Petaling Jaya

Japan:

Tokyo, Fukuoka, Osaka, Nagoya,

Saitama, Sendai

Europe:

London

Dynamics

T= 2𝜋 √[(4ML^3)/(bd^3E)]

Dynamics

T≈2𝜋 √(L/g)

Structure Dynamics

Interpretation of Spectra

Interpretation of Spectra

The Use of Structural Dynamics for information

leading to rational decision making

• All structures move all the time

• The movements contain information

• The information is recorded and decoded using an SKG

(StructuroCardiograph TM)

• The information is analogous to an EKG for humans

• Armed with information about the behavior and state of the

structure a management approach can be tailored to the needs

of the community

Structural Health Monitoring

• “Structural Health Monitoring (SHM) is defined as the use of

on-structure sensing system to monitor the performance of the

structure and evaluate its health state.” Chan, T

• Accelerometers, Anometers, Thermometers, Strain guages

• Statistical pattern recognition

– Operational Evaluation,

– Data Acquisition and Cleansing,

– Feature Extraction and Data Compression,

– Statistical Model Calibration

• Elastic range, Plastic range, discrete elements

Structural Health Monitoring

• Simple or Complex

• Discrete Element or Whole of Structure

• Instant in Time, Periodic or Continuous

• Granularity vs Data Volume

What is the intended Outcome of the monitoring?

- Types of instruments

- Sensitivity of instruments

- Record frequency

Structure Stiffness, Damping and Frequency

• We use the displacement per unit force

• For mode ‘r’

• It is like the ‘spring constant’ for the structure

𝑿𝒓𝑭𝒓

=𝟏

𝟖𝜻𝒓𝒇𝒓𝟐𝑴𝒓𝝅

𝟐

• In the elastic range 𝑴𝒓 is unchanging (so long as the mode shape is unchanging).

• Characteristic is a function of frequency and damping

From Local to Global

0

10

20

30

40

50

60

0 5 10 15 20 25 30 35

Mo

dal

Fo

rce

Modal Displacement

K

F’uF’c

Basic Theory underlying

STRAAM Technology

• Measurement of Frequencies of Resonance/

Dynamic Response

• Building and Calibrating Finite Element

Models

• The use of damping measurement as a

damage indicator

Basic Theory underlying

STRAAM Technology• Measurement of Frequencies of Resonance

– This allows the mathematical definition of the structure as it is

– Technically known as ‘Structural Identification’; Baseline

– Frequency change = loss of capacity

• The use of damping measurement as a damage indicator

– Damping is a measure of energy dissipation

– Damage causes energy dissipation

– STRAAM’s model of damping is based on fracture mechanics

• Build and Claibrate FEM– Memoralise as is condition and compare to design

Assessment of a structure – 8 steps

1. Determine design load

2. Estimate probability of occurrence of design load

3. Measure the response of the structure

4. Determine the displacement per unit force

5. Extrapolate from measured to reference displacement

6. Find the ratio of measured to design forces for reference

displacement

7. Determine the return period of an event that takes the

structure to the reference displacement

8. Apply a hazard assessment

Basis for alarms Changes in the 1st mode. Any alarm can be

created based on specific failure modes

Warning

Alarm

Bridge 1

Load Capacity:

Determine the structure’s performance and / or serviceability

under a range of different load conditions

comparison of “as-is” condition to the original design

Detection, if any, of specific damage

Two lane single span

Super T

Metropolitan road

Bridge 1

1. The Bridge was monitored on February 21st, 2017 for its

response to randomly induced actions from the

environment.

2. The response of the bridge was analysed so as to

establish its frequencies of resonance, the amount of

energy dissipation, and the overall response.

3. A reduced node finite element model (RNFEM) was

constructed, and the measured response was used to

calibrate the RNFEM.

4. The calibrated RNFEM was then used to assess the

response of the bridge to various combinations of T44,

and B Double induced loads.

5. The response of the bridge was found to be well inside

the performance indicators recommended by AASHTO, at

a maximum of 8.4 mm vertical displacement, against a

performance requirement of a maximum of 26.4 mm.

Bridge 1

1. Bridge remained open for duration of the data collection (one lane closed)

2. Time on site approximately 2 hours

3. An existing traffic control window was used (other works on bridge during data collection)

4. Ambient wind and traffic loads provided excitation of structure

Bridge 1

1. Harmonic frequencies for bridge (x, y and z) identified

2. Finite element model calibrated

3. Calibrated finite element model used to confirm bridge load capacity

4. Several load conditions modelled

Mode MeasFreq

RNFEM freq

% Diff

NS1 2.88 3.02 4.6

EW1 4.00 3.90 2.6

V1 4.61 4.61 0.0

V2 4.63 5.18 10.6

Bridge 1

1. Bridge is in good condition

2. Max deflection 8.4 mm for 22.8 m span, well within L/375 AASHTO requirement

3. Small anomalies suggest differing aging effects at the abutments

Bridge 2

Load Capacity:

Determine the structure’s performance and / or serviceability

under a range of different load conditions

comparison of “as-is” condition to the original design

Detection, if any, of specific damage

Two span, two lanes

Single box girder

Metropolitan road

Both abutments subsided

Central pier

Bridge 2

The bridge was monitored on November 13th, 2017 for its

response to randomly induced actions from the environment.

The response of the bridge was analysed so as to establish

its frequencies of resonance, the amount of energy

dissipation, and the overall response.

The results will be used to track the dynamic changes to the

bridge during the renovation process.

An anomaly at low amplitude is present in the Randec

Signature. This type of anomaly is generally indicative of a

weakness in the structure.

Bridge 2

1. Bridge remained open for duration of the data collection (one lane closed)

2. Time on site approximately 6 hours

3. A full bridge inspection was conducted by Hatch during the data acquisition

4. Ambient wind and traffic loads provided excitation of structure

Bridge 2

The following points should be noted for the measured structure:

1. The first vertical bending mode which is reflective of the load carrying capacity of the structure is identified at 2.47

Hz. The middle of the Eastern extremity is moving appoximatley 10% more than the Western extremity at the center of

the North Span.

2. The first translational mode of vibration is 3.86 Hz. This mode of vibration is concentrated in the center of the bridge

with minimal movement at the abutments. The column contributes directly to this mode’s defining parameters.

3. The first vertical anti-symmetric torsional mode is measured to be 5.35 Hz. This mode of vibration involves the

Eastern and Western extremities roatating about the center line of the bridge.

Bridge 2

1. The left abutment is displacing vertically slightly more than the right abutment

2. There is an anomaly between damping and frequency at low amplitude; frequency

decreases and damping increases. This anomaly is most likely due to loss of

energy at the abutment.

Bridge 2

The baseline response of the bridge has been detailed. The following points should be noted:

1. With the exception of the reported differential settlement of the abutments, there are a minimal

number of anomalies present in the recordings that indicate significate structural damage.

2. The first three modes of vibration have been characterized above and will be used as a baseline to

compare with future measurements.

3. The Randec Signature presented in Mode 1 shows an anomaly at low amplitude. This sudden

reduction in frequency and increase in damping generally indicates energy dissipation associated

with the interaction of the bridge with abutments (and therefore mainly the Northern one). As the

improvements to the structure conducted by Mainmark are progressing, changes to this anomaly

will be tracked and reported on.

Final points

1. Rapid, real-time, non evasive

2. Establish a ‘baseline’

3. Calibrated FEM

4. Quantify damage

5. Continuous monitoring

NON DESTRUCTIVE STRUCTURAL ASSESSMENT OF BRIDGES USING IN-SERVICE DYNAMIC RESPONSE